V A Kreye

Publications (10)34.97 Total impact

• Article: Antiarrhythmic drug carvedilol inhibits HERG potassium channels.

  C A Karle, V A Kreye, D Thomas, K Röckl, S Kathöfer, W Zhang, J Kiehn
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  ABSTRACT: The aryloxypropanolamine carvedilol is a multiple action cardiovascular drug with blocking effects on alpha-receptors, beta-receptors, Ca(2+)-channels, Na(+)-channels and various native cardiac K(+) channels, thereby prolonging the cardiac action potential. In a number of clinical trials with patients suffering from congestive heart failure, carvedilol appeared to be superior to other beta-blocking agents in reducing total mortality. Given the multiple pharmacological actions of carvedilol, this may be due to specific channel blockade rather than beta-antagonistic activity. Since human ether-a-go-go related gene (HERG) K(+)channels play a critical role in the pathogenesis of cardiac arrhythmias and sudden cardiac death, the effects of carvedilol on HERG K(+)channels were investigated. Double-electrode voltage-clamp experiments were performed on HERG potassium channels which were expressed heterologously in Xenopus oocytes. Carvedilol at a concentration of 10 microM blocked HERG potassium tail currents by 47%. The electrophysiological characteristics of HERG, i.e. activation, steady-state inactivation and recovery from inactivation were not affected by carvedilol. Inhibition of current gradually increased from 0% immediately after the test pulse to about 80% at 600 ms with subsequent marginal changes of current kinetics during the resting 29 s, indicating a very fast open channel block by carvedilol as the major blocking mechanism. This is the first study demonstrating that carvedilol blocks HERG potassium channels. The biophysical data presented in this study with a potentially antiarrhythmic effect may contribute to the positive outcome of clinical trials with carvedilol.
  Cardiovascular Research 03/2001; 49(2):361-70. · 6.06 Impact Factor
• Article: A K+ single channel and whole-cell clamp study on the effects of levocromakalim in guinea pig portal vein cells.

  C A Karle, X Yao, V A Kreye
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  ABSTRACT: Single channel cell-attached patch and whole-cell clamp experiments on the mode of action of the K+ channel opener (KCO), levcromakalim, were performed in guinea pig isolated portal vein cells. At +20 mV (135/23 mM K+ in bath/pipette), 10 microM levcromakalim activated K+ channels with a chord conductance of 23.2 pS (K(KCO)), which were sensitive to the blocker of ATP-dependent K+ channels (K(ATP)), glibenclamide. Voltage steps from -80 mV to +20 mV activated 4-aminopyridine-sensitive K+ channels of 6.5 pS with properties of delayed rectifier K+ channels (Kv). In patches which upon a previous voltage step had revealed the existence of Kv, levcromakalim reduced the open-probability of Kv, but it did not concomitantly activate K(KCO). During the course of the experiments, but unrelated to the presence of levcromakalim, large conductance K+ channels (BK(Ca)) appeared which could be inhibited by iberiotoxin, a selective blocker of BK(Ca), and by the membrane-permeant calcium buffer, BAPTA/AM, but not by glibenclamide. Whole-cell current-voltage (i-V) relations were established in response to voltage ramps from +50 mV to -100 mV; on subtraction of control i-V curves from i-V curves obtained in the presence of 10 microM levcromakalim, the KCO-induced K+ current remained which was proportional to voltage. This is not compatible with the upward-bent curvature predicted by the GHK current equation for purely resistive channels at high [K+]i versus low [K+]o. In conclusion, in the guinea pig portal vein cells, no evidence could be established for the hypotheses that KCOs may act via conversion of Kv to K(ATP) (Beech and Bolton 1989; Edwards et al. 1993) or by activation of BK(Ca) (Balwierczak et al. 1995). In these cells, mild inward rectification of the levcromakalim-induced current was observed which underlines their relationship to K(ATP) in other tissues.
  Archiv für Experimentelle Pathologie und Pharmakologie 10/1998; 358(3):374-81. · 2.65 Impact Factor
• Article: Intracellular ADP activates ATP-sensitive K+ channels in vascular smooth muscle cells of the guinea pig portal vein.

  D Pfründer, I Anghelescu, V A Kreye
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  ABSTRACT: Vasodilatation following tissue ischemia is assumed to partially result from activation of ATP-dependent K+ channels (KATP). To assess the effect of cytosolic adenosine nucleotides, the balance of which depends on tissue pO2, on KATP, we have measured steady state outward currents (SSC) by the whole-cell clamp technique in smooth muscle cells of the guinea pig portal vein at different concentrations of ATP and ADP in the pipette solution. Glibenclamide, a selective inhibitor of KATP, was used as a pharmacological tool. With no nucleotides in the pipette solution (Ca(2+)-free), the SSC determined at +20 mV was unaffected by glibenclamide, while with 0.1 mM ATP or with 0.1 mM ADP, the SSC exhibited a glibenclamide-sensitive component indicating activation of KATP. At 5 mM ATP and no ADP, hardly any effect of glibenclamide on the SSC was detected, suggesting inhibition of KATP by this high concentration of ATP. With 0.1 mM ADP at 5 mM ATP however, activation of KATP was achieved. At 10(-7) M Ca2+ in the pipette solution, an increased SSC was measured, but the responses to the nucleotides and/or glibenclamide were not modified. These findings suggest that in vivo, ADP may be involved in the regulation of vascular KATP, linking tissue pO2 with vascular tone and tissue perfusion.
  Pflügers Archiv - European Journal of Physiology 05/1993; 423(1-2):149-51. · 4.46 Impact Factor
• Article: Tedisamil inhibits the delayed rectifier K+ current in single smooth muscle cells of the guinea-pig portal vein.

  D Pfründer, V A Kreye
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  ABSTRACT: Tedisamil is a new bradycardic agent with an inhibitory action on K+ channels in cardiac muscle, and secondary beneficial effects in experimentally induced cardiac ischemia. In whole-cell clamp studies in enzymatically dispersed, single smooth muscle cells from the guinea-pig portal vein, tedisamil inhibited the delayed rectifier K+ current (determined as the charge transferred through the cell membrane), the mean concentration for half-maximal inhibition being 2.9 microM. In contrast to controls in the absence of drugs or in the presence of the classical K+ channel blockers barium, tetraethylammonium or 4-aminopyridine, the time course of the delayed rectifier K+ current in the presence of tedisamil could no longer be fitted by a single exponential, and signs of an accelerated inactivation by tedisamil were obtained. The slow onset of the response to tedisamil applied to the outside of the vascular myocytes, and the finding that tedisamil applied directly to the cytosol via the pipette was highly effective, suggest an intracellular site of action.
  Pflügers Archiv - European Journal of Physiology 06/1992; 421(1):22-5. · 4.46 Impact Factor
• Article: Effects of the K+ channel blocker tedisamil on 86Rb efflux induced by cromakalim, high potassium and noradrenaline, and on mechanical tension in rabbit isolated vascular smooth muscle.

  V A Kreye, D Pfründer, U Theiss
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  ABSTRACT: Tedisamil, a new bradycardic agent with an inhibitory action on K+ channels in cardiac muscle, was found to inhibit in a non-competitive manner the relaxation induced by the K+ channel opener cromakalim in noradrenaline-stimulated helical strips from rabbit aortae. Tedisamil tended to be more potent in this respect than glibenclamide; the latter however competitively antagonized the cromakalim-induced relaxation. In rabbit aorta preloaded with 86Rb as a marker of K+, 10 mumol/l tedisamil inhibited the 86Rb efflux induced by 10 mumol/l cromakalim. - While the 86Rb efflux evoked by depolarization with 100 mmol/l K+ aspartate was inhibited by tedisamil, too, the rise of 86Rb efflux induced by noradrenaline was unaffected by the drug. In non-stimulated rabbit aorta, tedisamil increased mechanical tension in a concentration-dependent manner (EC50 for peak contractions: 32 mumol/l; for maintained tension: 24 mumol/l), and enhanced 86Rb efflux. Both stimulant actions were antagonized by the calcium antagonist diltiazem. In conclusion, tedisamil affects different K+ channels in vascular smooth muscle. Its stimulant effects are assumed to be secondary to membrane depolarization and subsequent activation of voltage-dependent Ca2+ channels.
  Archiv für Experimentelle Pathologie und Pharmakologie 03/1992; 345(2):238-43. · 2.65 Impact Factor
• Article: Pharmacological characterization of nicorandil by 86Rb efflux and isometric vasorelaxation studies in vascular smooth muscle.

  V A Kreye, T Lenz, D Pfründer, U Theiss
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  ABSTRACT: Nicorandil and cromakalim were found to stimulate 86Rb efflux (a marker of K+ ions) from resting preparations of rabbit aorta. This action was suppressed by 10(-5) M glibenclamide, an antagonist of K(+)-channel openers in vascular smooth muscle. Through intracellular production of cyclic GMP, and subsequent suppression of cellular Ca2+ activation, nitrovasodilators interfere indirectly with the activation of Ca(2+)-dependent ion channels. 8-Bromo-cyclic GMP and sodium nitroprusside antagonized the Ca(2+)-dependent 86Rb efflux induced by 3 x 10(-7) M norepinephrine. When nicorandil and cromakalim were investigated in the same experimental setup in the presence of glibenclamide to suppress stimulation of K+ channels, only nicorandil also suppressed the norepinephrine-induced increase of the 86Rb efflux. These results confirm that nicorandil acts as both an opener of K+ channels and a nitrovasodilator. Nicorandil relaxed helical strips from rabbit aorta contracted by 10(-7) M norepinephrine, but in contrast to the relaxant action of cromakalim, this response was not antagonized by the use of glibenclamide, indicating a greater importance of the nitrovasodilator mechanism than of the K(+)-channel-opening activity for relaxation in this tissue. However, when the nitrate-like action of nicorandil was suppressed by 10(-5) M methylene blue, the K(+)-channel-opening activity was unmasked on addition of 10(-4) M glibenclamide at high concentrations of nicorandil.
  Journal of Cardiovascular Pharmacology 02/1992; 20 Suppl 3:S8-12. · 2.29 Impact Factor
• Article: Tedisamil blocks single large-conductance Ca(2+)-activated K+ channels in membrane patches from smooth muscle cells of the guinea-pig portal vein.

  D Pfründer, V A Kreye
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  ABSTRACT: Enzymatically dispersed smooth muscle cells of the guinea-pig portal vein were studied by the patch-clamp technique. They were found to have Ca(2+)-dependent K+ channels with the typical properties of the "BK" channel, i.e. a reversal potential at the calculated equilibrium potential for K+ ions, a striking voltage dependence, and a conductance of approximately 200 pS ([K+]o 50 mM, [K+]i 150 mM, positive patch potentials). Tedisamil, a new bradycardic agent with an inhibitory action on K+ currents in heart muscle, reduced the open probability of the BK channels concentration-dependently (1-100 microM) when applied at the cytosolic side of membrane inside-out patches. At 100 microM [Ca2+]i, the IC50 of tedisamil was 13.8 microM (mean, n = 5). Tedisamil increased the frequency of channel closures, and reduced the mean duration of openings from 8 ms to less than 1 ms, while the mean duration of closures within bursts (1-2 ms) was not altered. Tedisamil did not affect long closures (greater than 160 ms) between bursts, either. The mean time of residence of tedisamil at the BK channel was estimated to be 1-2 ms. Hence, tedisamil, in comparison to the "slow" blocker Ba2+ and the "fast" blocker tetraethylammonium, holds the position of an "intermediate" K+ channel blocker.
  Pflügers Archiv - European Journal of Physiology 06/1991; 418(4):308-12. · 4.46 Impact Factor
• Article: The dualistic mode of action of the vasodilator drug, nicorandil, differentiated by glibenclamide in 86Rb flux studies in rabbit isolated vascular smooth muscle.

  V A Kreye, T Lenz, U Theiss
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  ABSTRACT: (1) In rabbit isolated aorta, the effects of the antianginal drug, nicorandil, of the K+ channel opener, cromakalim, and of the nitrovasodilator, sodium nitroprusside, on 86Rb efflux and on contractile force were compared. (2) In ion flux studies using 86Rb as a marker of K+ ions, both nicorandil and cromakalim, but not sodium nitroprusside, increased the efflux of 86Rb in non-stimulated preparations. The increase of membrane K+ conductance induced by nicorandil and cromakalim was totally suppressed by 10(-5) mol/l of the sulfonylurea derivative, glibenclamide. (3) The vasoconstrictor drug, noradrenaline (3 x 10(-7) mol/l), effectively increased the rate of 86Rb efflux. This stimulatory response was unaffected by glibenclamide, but was totally inhibited by Ca2+ depletion suggesting that the activation of Ca2(+)-sensitive K+ channels was responsible for this action of noradrenaline. (4) Sodium nitroprusside and nicorandil, the latter in the presence of glibenclamide to suppress the glibenclamide-sensitive stimulatory component on 86Rb efflux, antagonized the noradrenaline-induced increase in 86Rb efflux, while cromakalim in the presence of glibenclamide had no effect. (5) All of the vasodilators relaxed rabbit aortic strips contracted by 10(-7) mol/l noradrenaline in a concentration-dependent manner. (6) The vasodilatory response to cromakalim was antagonized by glibenclamide, whereas the relaxant action of nicorandil and of sodium nitroprusside remained unaffected. (7) These results demonstrate that under particular experimental circumstances, nicorandil can behave in vascular smooth muscle both as an opener of glibenclamide-sensitive K+ channels, and as a directly acting nitrovasodilator which acts via reduction of cellular calcium levels.(ABSTRACT TRUNCATED AT 250 WORDS)
  Archiv für Experimentelle Pathologie und Pharmakologie 02/1991; 343(1):70-5. · 2.65 Impact Factor
• Article: Characterization of the K(+)-channel-coupled adenosine receptor in guinea pig atria.

  H Tawfik-Schlieper, K N Klotz, V A Kreye, U Schwabe
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  ABSTRACT: In the present work we studied the pharmacological profile of adenosine receptors in guinea pig atria by investigating the effect of different adenosine analogues on 86Rb(+)-efflux from isolated left atria and on binding of the antagonist radioligand 8-cyclopentyl-1,3-[3H]dipropylxanthine [( 3H]DPCPX) to atrial membrane preparations. The rate of 86Rb(+)-efflux was increased twofold by the maximally effective concentrations of adenosine receptor agonists. The EC50-values for 2-chloro-N6-cyclopentyladenosine (CCPA), R-N6-phenylisopropyladenosine (R-PIA), 5'-N-ethylcarboxamidosadenosine (NECA), and S-N6-phenylisopropyladenosine (S-PIA) were 0.10, 0.14, 0.24 and 12.9 microM, respectively. DPCPX shifted the R-PIA concentration-response curve to the right in a concentration-dependent manner with a KB-value of 8.1 nM, indicating competitive antagonism. [3H]DPCPX showed a saturable binding to atrial membranes with a Bmax-value of 227 fmol/mg protein and a KD-value of 1.3 nM. Competition experiments showed a similar potency for the three agonists CCPA, R-PIA and NECA. S-PIA is 200 times less potent than R-PIA. Our results suggest that the K+ channel-coupled adenosine receptor in guinea pig atria is of an A1 subtype.
  Archiv für Experimentelle Pathologie und Pharmakologie 01/1990; 340(6):684-8. · 2.65 Impact Factor
• Article: Inhibition of the contraction of the isolated longitudinal muscle of the guinea-pig ileum by botulinum C2 toxin: evidence for a role of G/F-actin transition in smooth muscle contraction.

  S Mauss, G Koch, V A Kreye, K Aktories
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  ABSTRACT: The effect of botulinum C2 toxin was studied on the contractions of the guinea pig ileum myenteric plexus longitudinal muscle preparation. Botulinum C2 toxin inhibited the muscle contraction induced by electrical stimulation (60 V; 0.5 ms; 0.33 Hz) in a time and concentration dependent manner. The inhibitory effect occurred with a time lag of about 1 h, and depended on the presence of both toxin components. After 4 h of incubation with 1.7 micrograms/ml of component I and 6.7 micrograms/ml of component II of botulinum C2 toxin, the smooth muscle contraction was inhibited by about 60%. At these toxin concentrations, about 55% of the modifiable smooth muscle actin was ADP-ribosylated. Smooth muscle contraction induced by bradykinin and bethanechol were similarly inhibited. Moreover, the C2 toxin inhibited muscle contraction induced by Ba2+, and by direct muscle membrane depolarization (60 V; 10 ms; 0.33 Hz) after suppression of acetylcholine release by normorphine. Also cytochalasin D inhibited the electrically evoked contraction of the ileum longitudinal muscle. In contrast to botulinum C2 toxin, inhibition of contractility by cytochalasin D occurred without a lag phase, and was reversed by washing off the toxin. In contrast of guinea pig ileum longitudinal muscle, botulinum C2 toxin did not reduce the contraction of the rabbit aortic smooth muscle stimulated by K+-depolarization or noradrenaline.
  Archiv für Experimentelle Pathologie und Pharmakologie 10/1989; 340(3):345-51. · 2.65 Impact Factor