M L Garcia

Temple University, Philadelphia, PA, United States

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Publications (57)240.88 Total impact

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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 08/2010; 26(34). DOI:10.1002/chin.199534212
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    ABSTRACT: The gene cluster required for paxilline biosynthesis in Penicillium paxilli contains two cytochrome P450 monooxygenase genes, paxP and paxQ. The primary sequences of both proteins are very similar to those of proposed cytochrome P450 monooxygenases from other filamentous fungi, and contain several conserved motifs, including that for a haem-binding site. Alignment of these sequences with mammalian and bacterial P450 enzymes of known 3-D structure predicts that there is also considerable conservation at the level of secondary structure. Deletion of paxP and paxQ results in mutant strains that accumulate paspaline and 13-desoxypaxilline, respectively. These results confirm that paxP and paxQ are essential for paxilline biosynthesis and that paspaline and 13-desoxypaxilline are the most likely substrates for the corresponding enzymes. Chemical complementation of paxilline biosynthesis in paxG (geranygeranyl diphosphate synthase) and paxP, but not paxQ, mutants by the external addition of 13-desoxypaxilline confirms that PaxG and PaxP precede PaxQ, and are functionally part of the same biosynthetic pathway. A pathway for the biosynthesis of paxilline is proposed on the basis of these and earlier results. Electrophysiological experiments demonstrated that 13-desoxypaxilline is a weak inhibitor of mammalian maxi-K channels (Ki=730 nM) compared to paxilline (Ki=30 nM), indicating that the C-13 OH group of paxilline is crucial for the biological activity of this tremorgenic mycotoxin. Paspaline is essentially inactive as a channel blocker, causing only slight inhibition at concentrations up to 1 microM.
    Molecular Genetics and Genomics 11/2003; 270(1):9-23. DOI:10.1007/s00438-003-0887-2 · 2.83 Impact Factor
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    Toxicon 07/2001; 39(6):739-48. DOI:10.1016/S0041-0101(00)00214-2 · 2.58 Impact Factor
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    ABSTRACT: The maxi-K channel from bovine aortic smooth muscle consists of a pore-forming alpha subunit and a regulatory beta1 subunit that modifies the biophysical and pharmacological properties of the alpha subunit. In the present study, we examine ChTX-S10A blocking kinetics of single maxi-K channels in planar lipid bilayers from smooth muscle or from tsA-201 cells transiently transfected with either alpha or alpha+beta 1 subunits. Under low external ionic strength conditions, maxi-K channels from smooth muscle showed ChTX-S10A block times, 48 +/- 12 s, that were similar to those expressing alpha+beta 1 subunits, 51 +/- 16 s. In contrast, with the alpha subunit alone, ChTX-S10A block times were much shorter, 5 +/- 0.6 s, and were qualitatively similar to previously reported values for the skeletal muscle maxi-K channel. Increasing the external ionic strength caused a decrease in ChTX-S10A block times for maxi-K channel complexes of alpha+beta 1 subunits but not of alpha subunits alone. These findings indicate that it may be possible to predict the association of beta 1 subunits with native maxi-K channels by monitoring the kinetics of ChTX blockade of single channels, and they suggest that maxi-K channels in skeletal muscle do not contain a beta 1 subunit like the one present in smooth muscle. To further test this hypothesis, we examined the binding and cross-linking properties of [(125)I]-IbTX-D19Y/Y36F to both bovine smooth muscle and rabbit skeletal muscle membranes. [(125)I]-IbTX-D19Y/Y36F binds to rabbit skeletal muscle membranes with the same affinity as it does to smooth muscle membranes. However, specific cross-linking of [(125)I]-IbTX-D19Y/Y36F was observed into the beta 1 subunit of smooth muscle but not in skeletal muscle. Taken together, these data suggest that studies of ChTX block of single maxi-K channels provide an approach for characterizing structural and functional features of the alpha/beta 1 interaction.
    Biochemistry 06/2000; 39(20):6115-22. · 3.19 Impact Factor
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    ABSTRACT: Correolide, a novel nortriterpene natural product, potently inhibits the voltage-gated potassium channel, K(v)1.3, and [(3)H]dihydrocorreolide (diTC) binds with high affinity (K(d) approximately 10 nM) to membranes from Chinese hamster ovary cells that express K(v)1.3 (Felix, J. P., Bugianesi, R. M., Schmalhofer, W. A., Borris, R., Goetz, M. A., Hensens, O. D., Bao, J.-M., Kayser, F. , Parsons, W. H., Rupprecht, K., Garcia, M. L., Kaczorowski, G. J., and Slaughter, R. S. (1999) Biochemistry 38, 4922-4930). Mutagenesis studies were used to localize the diTC binding site and to design a high affinity receptor in the diTC-insensitive channel, K(v)3.2. Transferring the pore from K(v)1.3 to K(v)3.2 produces a chimera that binds peptidyl inhibitors of K(v)1.3 with high affinity, but not diTC. Transfer of the S(5) region of K(v)1.3 to K(v)3.2 reconstitutes diTC binding at 4-fold lower affinity as compared with K(v)1.3, whereas transfer of the entire S(5)-S(6) domain results in a normal K(v)1.3 phenotype. Substitutions in S(5)-S(6) of K(v)1.3 with nonconserved residues from K(v)3.2 has identified two positions in S(5) and one in S(6) that cause significant alterations in diTC binding. High affinity diTC binding can be conferred to K(v)3.2 after substitution of these three residues with the corresponding amino acids found in K(v)1.3. These results suggest that lack of sensitivity of K(v)3.2 to diTC is a consequence of the presence of Phe(382) and Ile(387) in S(5), and Met(458) in S(6). Inspection of K(v)1.1-1.6 channels indicates that they all possess identical S(5) and S(6) domains. As expected, diTC binds with high affinity (K(d) values 7-21 nM) to each of these homotetrameric channels. However, the kinetics of binding are fastest with K(v)1.3 and K(v)1.4, suggesting that conformations associated with C-type inactivation will facilitate entry and exit of diTC at its binding site. Taken together, these findings identify K(v)1 channel regions necessary for high affinity diTC binding, as well as, reveal a channel conformation that markedly influences the rate of binding of this ligand.
    Journal of Biological Chemistry 10/1999; 274(36):25237-44. · 4.60 Impact Factor
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    ABSTRACT: Potent and selective peptidyl blockers of the Shaker-type (Kv1) voltage-gated potassium channels were used to determine the role of these channels in regulating the spontaneous motility of smooth muscle preparations. Margatoxin (MgTX), kaliotoxin, and agitoxin-2 at 1 to 10 nM and agitoxin-1 at 50 to 100 nM induce twitches in guinea pig ileum strips. These twitches are abolished by tetrodotoxin (TTX, 0.5 microM), atropine (1 microM), hexamethonium (10 microM), or nifedipine (0.1 microM). It is proposed that blockade of Kv1 channels by MgTX, kaliotoxin, or the agitoxins increases excitability of intramural nerve plexuses in the ileum, promoting release of acetylcholine from excitatory motor nerve terminals. This, in turn, leads to Ca2+-dependent action potentials and twitching of the muscle fibers. MgTX does not induce twitches in several other guinea pig and/or rat vascular, genitourinary, or gastrointestinal smooth muscles, although small increases in spontaneous myogenic activity may be seen in detrusor muscle exposed to >30 nM MgTX. This effect is not reversed by TTX or atropine. The TTX- and atropine-sensitive twitches of guinea pig ileum are also induced by nanomolar concentrations of alpha-dendrotoxin, a selective blocker of Shaker Kv1.1 and 1.2 subtypes, or stichodactylatoxin, a peptide isolated from sea anemone that displays high affinity for Kv1.1 and 1.3, but not by charybdotoxin, which blocks Kv1.2 and 1.3 but not 1.1. The data taken together suggest that high-affinity blockade of Kv1.1 underlies the ability of MgTX, kaliotoxin, agitoxin-1, agitoxin-2, alpha-dendrotoxin, and stichodactylatoxin to elicit TTX-sensitive twitches in guinea pig ileum.
    Journal of Pharmacology and Experimental Therapeutics 06/1999; 289(3):1517-22. · 3.86 Impact Factor
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    Methods in Enzymology 02/1999; 294:274-87. DOI:10.1016/S0076-6879(99)94017-X · 2.19 Impact Factor
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    ABSTRACT: The search for peptidyl inhibitors of K+ channels is a very active area of investigation. In addition to scorpion venoms, other venom sources have been investigated; all of these sources have yielded novel peptides with interesting properties. For instance, spider venoms have provided peptides that block other families of K+ channels (e.g., Kv2 and Kv4) that act via mechanisms which modify the gating properties of these channels. Such inhibitors bind to a receptor on the channel that is different from the pore region in which the peptides discussed in this chapter bind. In fact, it is possible to have a channel occupied simultaneously by both inhibitor types. It is expected that many of the methodologies concerning peptidyl inhibitors from scorpion venom, which have been developed in the past and outlined above, will be extended to the new families of K+ channel blockers currently under development.
    Methods in Enzymology 02/1999; 294:624-39. DOI:10.1016/S0076-6879(99)94035-1 · 2.19 Impact Factor
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    ABSTRACT: Coexpression of alpha and beta subunits of the high conductance Ca2+-activated K+ (maxi-K) channel leads to a 50-fold increase in the affinity for 125I-charybdotoxin (125I-ChTX) as compared with when the alpha subunit is expressed alone (Hanner, M., Schmalhofer, W. A., Munujos, P., Knaus, H.-G., Kaczorowski, G. J., and Garcia, M. L. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 2853-2858). To identify those residues in the beta subunit that are responsible for this change in binding affinity, Ala scanning mutagenesis was carried out along the extracellular loop of beta, and the resulting effects on 125I-ChTX binding were determined after coexpression with the alpha subunit. Mutagenesis of each of the four Cys residues present in the loop causes a large reduction in toxin binding affinity, suggesting that these residues could be forming disulfide bridges. The existence of two disulfide bridges in the extracellular loop of beta was demonstrated after comparison of reactivities of native beta and single-Cys-mutated subunits to N-biotin-maleimide. Negatively charged residues in the loop of beta, when mutated individually or in combinations, had no effect on toxin binding with the exception of Glu94, whose alteration modifies kinetics of ligand association and dissociation. Further mutagenesis studies targeting individual residues between Cys76 and Cys103 indicate that four positions, Leu90, Tyr91, Thr93, and Glu94 are critical in conferring high affinity 125I-ChTX binding to the alpha.beta subunit complex. Mutations at these positions cause large effects on the kinetics of ligand association and dissociation, but they do not alter the physical interaction of beta with the alpha subunit. All these data, taken together, suggest that the large extracellular loop of the maxi-K channel beta subunit has a restricted conformation. Moreover, they are consistent with the view that four residues appear to be important for inducing an appropriate conformation within the alpha subunit that allows high affinity ChTX binding.
    Journal of Biological Chemistry 07/1998; 273(26):16289-96. DOI:10.1074/jbc.273.26.16289 · 4.60 Impact Factor
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    ABSTRACT: Five novel peptidyl inhibitors of Shaker-type (Kv1) K+ channels have been purified to homogeneity from venom of the scorpion Centruroides limbatus. The complete primary amino acid sequence of the major component, hongotoxin-1 (HgTX1), has been determined and confirmed after expression of the peptide in Escherichia coli. HgTX1 inhibits 125I-margatoxin binding to rat brain membranes as well as depolarization-induced 86Rb+ flux through homotetrameric Kv1.1, Kv1. 2, and Kv1.3 channels stably transfected in HEK-293 cells, but it displays much lower affinity for Kv1.6 channels. A HgTX1 double mutant (HgTX1-A19Y/Y37F) was constructed to allow high specific activity iodination of the peptide. HgTX1-A19Y/Y37F and monoiodinated HgTX1-A19Y/Y37F are equally potent in inhibiting 125I-margatoxin binding to rat brain membranes as HgTX1 (IC50 values approximately 0.3 pM). 125I-HgTX1-A19Y/Y37F binds with subpicomolar affinities to membranes derived from HEK-293 cells expressing homotetrameric Kv1.1, Kv1.2, and Kv1.3 channels and to rat brain membranes (Kd values 0.1-0.25 pM, respectively) but with lower affinity to Kv1.6 channels (Kd 9.6 pM), and it does not interact with either Kv1.4 or Kv1.5 channels. Several subpopulations of native Kv1 subunit oligomers that contribute to the rat brain HgTX1 receptor have been deduced by immunoprecipitation experiments using antibodies specific for Kv1 subunits. HgTX1 represents a novel and useful tool with which to investigate subclasses of voltage-gated K+ channels and Kv1 subunit assembly in different tissues.
    Journal of Biological Chemistry 02/1998; 273(5):2639-44. DOI:10.1074/jbc.273.5.2639 · 4.60 Impact Factor
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    ABSTRACT: Neurons require specific patterns of K+ channel subunit expression as well as the precise coassembly of channel subunits into heterotetrameric structures for proper integration and transmission of electrical signals. In vivo subunit coassembly was investigated by studying the pharmacological profile, distribution, and subunit composition of voltage-gated Shaker family K+ (Kv1) channels in rat cerebellum that are labeled by 125I-margatoxin (125I-MgTX; Kd, 0.08 pM). High-resolution receptor autoradiography showed spatial receptor expression mainly in basket cell terminals (52% of all cerebellar sites) and the molecular layer (39% of sites). Sequence-directed antibodies indicated overlapping expression of Kv1. 1 and Kv1.2 in basket cell terminals, whereas the molecular layer expressed Kv1.1, Kv1.2, Kv1.3, and Kv1.6 proteins. Immunoprecipitation experiments revealed that all 125I-MgTX receptors contain at least one Kv1.2 subunit and that 83% of these receptors are heterotetramers of Kv1.1 and Kv1.2 subunits. Moreover, 33% of these Kv1.1/Kv1.2-containing receptors possess either an additional Kv1.3 or Kv1.6 subunit. Only a minority of the 125I-MgTX receptors (<20%) seem to be homotetrameric Kv1.2 channels. Heterologous coexpression of Kv1.1 and Kv1.2 subunits in COS-1 cells leads to the formation of a complex that combines the pharmacological profile of both parent subunits, reconstituting the native MgTX receptor phenotype. Subunit assembly provides the structural basis for toxin binding pharmacology and can lead to the association of as many as three distinct channel subunits to form functional K+ channels in vivo.
    Journal of Biological Chemistry 10/1997; 272(44):27577-81. DOI:10.1074/jbc.272.44.27577 · 4.60 Impact Factor
  • Advances in pharmacology (San Diego, Calif.) 02/1997; 39:425-71. DOI:10.1016/S1054-3589(08)60078-2
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    ABSTRACT: Tissue expression and distribution of the high-conductance Ca(2+)-activated K+ channel Slo was investigated in rat brain by immunocytochemistry, in situ hybridization, and radioligand binding using the novel high-affinity (Kd 22 pM) ligand [3H]iberiotoxin-D19C ([3H]IbTX-D19C), which is an analog of the selective maxi-K peptidyl blocker IbTX. A sequence-directed antibody directed against Slo revealed the expression of a 125 kDa polypeptide in rat brain by Western blotting and precipitated the specifically bound [3H]IbTX-D19C in solubilized brain membranes. Slo immunoreactivity was highly concentrated in terminal areas of prominent fiber tracts: the substantia nigra pars reticulata, globus pallidus, olfactory system, interpeduncular nucleus, hippocampal formation including mossy fibers and perforant path terminals, medial forebrain bundle and pyramidal tract, as well as cerebellar Purkinje cells. In situ hybridization indicated high levels of Slo mRNA in the neocortex, olfactory system, habenula, striatum, granule and pyramidal cell layer of the hippocampus, and Purkinje cells. The distribution of Slo protein was confirmed in microdissected brain areas by Western blotting and radioligand-binding studies. The latter studies also established the pharmacological profile of neuronal Slo channels. The expression pattern of Slo is consistent with its targeting into a presynaptic compartment, which implies an important role in neural transmission.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 03/1996; 16(3):955-63. · 6.75 Impact Factor
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    ABSTRACT: Purified high conductance calcium-activated potassium (maxi-K) channels from tracheal smooth muscle have been shown to consist of a 60-70-kDa alpha subunit, encoded by the slo gene, and a 31-kDa beta subunit. Although the size of the beta subunit is that expected for the product of the gene encoding this protein, the size of the alpha subunit is smaller than that predicted from the slo coding region. To determine the basis for this discrepancy, sequence-directed antibodies have been raised against slo. These antibodies specifically precipitate the in vitro translation product of mslo, which yields an alpha subunit of the expected molecular mass (135 kDa). Immunostaining experiments employing smooth muscle sarcolemma, skeletal muscle T-tubules, as well as membranes derived from GH3 cells reveal the presence of an alpha subunit with an apparent molecular mass of 125 kDa. The difference in size of the alpha subunit as expressed in these membranes and the purified preparations is due to a highly reproducible proteolytic decay that occurs mostly at an advanced stage of the maxi-K channel purification. In the purified maxi-K channel preparations investigated, the full-length alpha subunit, an intermediate size product of 90 kDa, and the 65-kDa polypeptide, as well as other smaller fragments can be detected using appropriate antibodies. Proteolysis occurs exclusively at two distinct positions within the long C-terminal tail of slo. In addition, evidence for the tissue expression of distinct splice variants in membrane-bound as well as purified maxi-K channels is presented.
    Journal of Biological Chemistry 10/1995; 270(38):22434-9. DOI:10.1074/jbc.270.38.22434 · 4.60 Impact Factor
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    ABSTRACT: High-conductance calcium-activated potassium (maxi-K) channels are composed of two subunits, alpha and beta. The pore-forming alpha subunit is a member of the mSlo family of K+ channels, whereas the beta subunit is a novel protein that modulates the biophysical and pharmacological properties of the channel complex. In the presence of a bifunctional cross-linking reagent, monoiodotyrosine charybdotoxin ([125I]ChTX) is covalently incorporated specifically into Lys69 of the beta subunit, which is located in a large extracellular loop of this protein. Using variants of ChTX which retain their channel-blocking activity and in which individual Lys residues have been mutated, we have identified the corresponding amino acid in ChTX that is involved in the cross-linking reaction. All of the ChTX mutants investigated bind to the maxi-K channel and display the same pharmacological profile as native ChTX in competition binding experiments. Whereas substitution of amino acids at positions 11 and 31 of ChTX yields wild-type cross-linking patterns, the peptide without a Lys at position 32 fails to incorporate into the beta subunit of the maxi-K channel. Given the model for the interaction between ChTX and the outer vestibule of the maxi-K channel that has been proposed (Stampe et al., 1994), our data constrain the maximum distance between the pore of this channel and the region in the extracellular loop of the beta subunit where the cross-linking reaction takes place to 11 A. This topological limit helps define structural features of the maxi-K channel that may aide in probing the functional interaction between alpha and beta subunits of the channel complex.
    Biochemistry 09/1995; 34(34):10771-6. · 3.19 Impact Factor
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    ABSTRACT: Over the last few years, a considerable amount of information has been obtained regarding K+ channels. Different areas of research have contributed to knowledge in this field. Charybdotoxin (ChTX), a 37-amino acid peptide isolated from venom of the scorpion Leiurus quinquestriatus var. hebraeus, represents a remarkable tool for studying K+ channels. With its use, it has been possible to purify the high-conductance Ca(2+)-activated K+ (maxi-K) channel to homogeneity and determine the subunit composition of this channel. This has led to the discovery of an auxiliary beta-subunit that, when coexpressed with the pore-forming subunit, mSlo, alters the biophysical and pharmacological properties of this latter subunit. With the feasibility of producing large amounts of ChTX by recombinant techniques and the knowledge of the three-dimensional structure of the peptide, it has been possible to carry out site-directed mutagenesis studies and obtain a picture of the interaction surface of the toxin with two channels, maxi-K and Shaker, and to derive a picture of the complementary surface of the receptor in these two channels. Finally, ChTX, and the more selective K+ channel toxins that were subsequently discovered, have provided us with unique tools not only to determine the functional role that K+ channels play in target tissues but also to develop the molecular pharmacology of these channels.
    The American journal of physiology 08/1995; 269(1 Pt 1):C1-10. · 3.28 Impact Factor
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    ABSTRACT: cDNAs encoding functional maxi KCa channel alpha-subunits (hslo) were cloned from human myometrium. Northern blot analysis revealed a high abundance of mRNA in human uterine smooth muscle. Calcium- and voltage-activated K+ currents were recorded from Xenopus laevis oocytes injected with hslo cRNA and compared with currents after reconstitution of oocyte membranes expressing cloned maxi KCa channels. The expressed channels displayed characteristics of native maxi KCa channels, including large conductance (280 pS in symmetrical 110 mM K+), calcium sensitivity, kinetics and pharmacology. Currents were activated by niflumic acid; blocked by tetraethylammonium, charybdotoxin and iberiotoxin; and were insensitive to lemakalim, pinacidil, apamin and 4-aminopyridine. Coexpression with the beta-subunit, cloned from bovine trachea smooth muscle, dramatically increased the apparent calcium sensitivity as evident from a leftward shift of the voltage-activation curves. Half maximal activation (V1/2), measured in 10 microM Ca2+, was 12 +/- 18 mV (+/- SD, n = 62) for the alpha-subunit alone and -87 +/- 10 mV (+/- SD, n = 39) in presence of the beta-subunit.
    Receptors and Channels 02/1995; 3(3):185-99.
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    ABSTRACT: Purified high conductance Ca(2+)-activated K+ (maxi-K) channels from bovine tracheal smooth muscle have been covalently labeled employing monoiodotyrosine charybdotoxin ([125I]ChTX) and different bifunctional cross-linking reagents. [125I]ChTX was specifically incorporated into the beta-subunit, which was thereafter isolated by size exclusion high performance liquid chromatography. Proteolytic fragments of the [125I]ChTX-labeled beta-subunit were generated by digestion with various endoproteinases. Glu-C or Asp-N cleavage yielded a glycosylated [125I]ChTX-labeled fragment of 13-14 kDa. A site-directed antiserum raised against residues 62-75 of the cloned beta-subunit of the maxi-K channel specifically recognizes the beta-subunit in immunostaining experiments and was capable of immunoprecipitating these ChTX-labeled peptides. Lys-C cleavage resulted in two fragments of 16 and 28 kDa, respectively, which were both precipitated by anti-beta (62-75). However, only the 28-kDa fragment was recognized by anti-beta(118-132) and shown to carry double the amount of N-linked carbohydrates. Taken together, these data restrict the site of covalent incorporation of ChTX into the beta-subunit exclusively at Lys69, confirm the predicted topology of this subunit, and indicate that both canonical N-linked glycosylation sites are occupied with complex carbohydrates of 5-6 kDa each. We propose that an extracellularly located portion of the beta-subunit is located within 7.7 A of the ChTX receptor site and could even participate in the formation of this receptor by close apposition of its extracellular domain with structural elements provided by the alpha-subunit.
    Journal of Biological Chemistry 10/1994; 269(37):23336-41. · 4.60 Impact Factor
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    ABSTRACT: The charybdotoxin receptor, purified from bovine tracheal smooth muscle, consists of two subunits (alpha and beta) and, when reconstituted into planar lipid bilayers, forms functional high conductance Ca(2+)-activated K+ channels. Amino acid sequence, obtained from proteolytic fragments of the beta-subunit, was used to design oligonucleotide probes with which cDNAs encoding this protein were isolated. The cDNAs encode a protein of 191 amino acids that contains two hydrophobic (putative transmembrane) domains and bears little sequence homology to subunits of other known ion channels. Site-directed antisera, raised against putative extracellular epitopes of this protein, specifically immunoprecipitated 125I-labeled Bolton-Hunter beta-subunit as well as [125I]charybdotoxin-cross-linked beta-subunit. Under nondenaturing conditions, however, these anti-beta sera immunoprecipitated a complex consisting of both the alpha- and beta-subunits. The data demonstrate that, in vivo, the high conductance Ca(2+)-activated K+ channel exists as a multimer containing both alpha- and beta-subunits, and this cDNA represents the first beta-subunit of a potassium channel cloned to date. Furthermore, we demonstrate that the cloned protein is the subunit to which charybdotoxin is specifically and covalently incorporated when cross-linked to the channel.
    Journal of Biological Chemistry 07/1994; 269(25):17274-8. · 4.60 Impact Factor
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    ABSTRACT: Target inactivation analysis was used to determine the functional size of the charybdotoxin (ChTX) receptor in aortic and tracheal sarcolemmal membrane vesicles. This receptor has previously been shown to be an integral component of the high-conductance Ca2+-activated K+ (Maxi-K) channel in these smooth muscles. Exposure of either bovine aortic or bovine tracheal sarcolemma to high-energy irradiation results in disappearance of 125I-labeled ChTX binding activity as a monoexponential function of radiation dose; from these functions molecular masses of 88 +/- 10 kDa and 89 +/- 6 kDa, respectively, can be calculated. Similar results were obtained from radiation inactivation studies with the detergent-solubilized ChTX receptor from aortic sarcolemmal membranes. The effect of radiation on 125I-labeled ChTX binding is to decrease the number of functional ChTX receptors without affecting the affinity of receptors for the toxin, indicating that radiation is destroying, rather than altering, the binding site. The validity of the radiation inactivation technique in these membrane preparations is supported by data obtained in parallel experiments in which target sizes of the alpha 1 subunit of the L-type Ca2+ channel and 5'-nucleotidase were measured. The molecular masses determined for these entities are in excellent agreement with those expected from previous studies. The present data are discussed in terms of the recently determined subunit composition of the smooth muscle Maxi-K channel. In light of the target size, a single alpha beta subunit heterodimer complex could serve as the ChTX receptor.
    Proceedings of the National Academy of Sciences 06/1994; 91(11):4718-22. DOI:10.1073/pnas.91.11.4718 · 9.81 Impact Factor

Publication Stats

3k Citations
240.88 Total Impact Points


  • 2000
    • Temple University
      • Department of Biochemistry
      Philadelphia, PA, United States
  • 1991–1999
    • Federal University of Rio de Janeiro
      Rio de Janeiro, Rio de Janeiro, Brazil
    • University of Pennsylvania
      • Department of Physiology
      Philadelphia, PA, United States
  • 1995
    • University of Innsbruck
      Innsbruck, Tyrol, Austria
  • 1993
    • University of Prince Edward Island
      Charlottetown, Prince Edward Island, Canada
  • 1980
    • Roche Institute of Molecular Biology
      Nutley, New Jersey, United States