Article

Regulation of cardiac L-type Ca2+ channel by coexpression of G(alpha s) in Xenopus oocytes.

Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Israel.
FEBS Letters (Impact Factor: 3.58). 03/1999; 444(1):78-84.
Source: PubMed

ABSTRACT Activation of G(alpha s) via beta-adrenergic receptors enhances the activity of cardiac voltage-dependent Ca2+ channels of the L-type, mainly via protein kinase A (PKA)-dependent phosphorylation. Contribution of a PKA-independent effect of G(alpha s) has been proposed but remains controversial. We demonstrate that, in Xenopus oocytes, antisense knockdown of endogenous G(alpha s) reduced, whereas coexpression of G(alpha s) enhanced, currents via expressed cardiac L-type channels, independently of the presence of the auxiliary subunits alpha2/delta or beta2A. Coexpression of G(alpha s) did not increase the amount of alpha1C protein in whole oocytes or in the plasma membrane (measured immunochemically). Activation of coexpressed beta2 adrenergic receptors did not cause a detectable enhancement of channel activity; rather, a small cAMP-dependent decrease was observed. We conclude that coexpression of G(alpha s), but not its acute activation via beta-adrenergic receptors, enhances the activity of the cardiac L-type Ca2+ channel via a PKA-independent effect on the alpha1C subunit.

0 0
 · 
0 Bookmarks
 · 
37 Views
  • [show abstract] [hide abstract]
    ABSTRACT: Altering voltage-gated ion channel currents, by changing channel number or voltage-dependent kinetics, regulates the propagation of action potentials along the plasma membrane of individual cells and from one cell to its neighbors. Functional increases in the number of cardiac sodium channels (Na(V)1.5) at the myocardial sarcolemma are accomplished by the regulation of caveolae by beta adrenergically stimulated G-proteins. We demonstrate that Na(V)1.5, Ca(V)1.2a, and K(V)1.5 channels specifically localize to isolated caveolar membranes, and to punctate regions of the sarcolemma labeled with caveolin-3. In addition, we show that Na(V)1.5, Ca(V)1.2a, and K(V)1.5 channel antibodies label the same subpopulation of isolated caveolae. Plasma membrane sheet assays demonstrate that Na(V)1.5, Ca(V)1.2a, and K(V)1.5 cluster with caveolin-3. This may have interesting implications for the way in which adrenergic pathways alter the cardiac action potential morphology and the velocity of the excitatory wave.
    Journal of Cardiovascular Electrophysiology 06/2006; 17 Suppl 1:S34-S42. · 3.48 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: This study was designed to compare the effects of purified antibodies against the beta(1)-adrenoceptor autoantibodies and total immunoglobulin G obtained during immunoadsorption on L-type Ca(2+) currents, action potentials and cell shortening, in rat ventricular myocytes. Patients with dilated cardiomyopathy frequently develop autoantibodies against beta(1)-adrenoceptors, which can be removed by immunoadsorption. There is some controversy, however, whether the beneficial effects of this therapeutic option are due to the removal of cardiostimulatory or cardiodepressive antibodies. Therefore we studied the effects of immunoglobulin G on two of the regulators of excitation-contraction coupling and on cell shortening. Immunoglobulin G was obtained during immunoadsorption therapy. Dissociated myocytes from rat hearts were electrically stimulated and cell shortening was measured by cell edge detection. Single electrode patch clamp technique in current or voltage clamp mode was used to measure L-type Ca(2+) currents or action potentials, respectively. (-)-Isoprenaline was used for comparative purposes. In comparison to (-)-isoprenaline, immunoglobulin G increased Ca(2+) current to a similar extent, but prolonged the plateau duration of action potentials to a lesser extent. Immunoglobulin G and beta(1)-adrenoceptor enhanced cell shortening to a similar degree, however, the effects were smaller than with (-)-isoprenaline. The increase in contraction amplitude was prevented by (-)-bisoprolol. We conclude that both beta(1)-adrenoceptors and immunoglobulin G derived from patients positive for beta(1)-adrenoceptor autoantibodies mediate the cardiostimulatory effects via beta(1)-adrenoceptors.
    Basic &amp Clinical Pharmacology &amp Toxicology 07/2005; 96(6):445-52. · 2.12 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: High plasma homocysteine levels are a known risk factor in heart failure and sudden cardiac death. The G proteins, G(s) (stimulatory) and G(i) (inhibitory), are involved in calcium regulation; overexpression has pathological consequences. The aims of this study were to examine the differential expression of G(s) G protein and G(i) in the hearts of hyperhomocysteinemic (Hhcy) mice, and to determine if homocysteine (Hcy) acts as an agonist in cell culture to mediate the change in G protein isoforms. To create Hhcy, heterozygous cystathionine-beta-synthase (CBS) knockout (KO) mice were used. Mice were sacrificed, hearts were excised, cardiac tissue homogenates were prepared, and Western blots were performed. The results suggested that G(s) G protein was downregulated in cardiac tissue of heterozygous CBS KO mice to 46% that of control hearts. However, the intracellular G(i) G protein content remained the same in heterozygous CBS KO mice. Transformed cardiomyocyte HL-1 cells were treated with varying concentrations of homocysteine. The results suggested no detectable differential G(s) and G(i) expression. This suggested that Hcy did not act as an agonist in vitro to alter G protein content, but that Hcy produced some other in vivo effects to incur these results.
    Vascular Health and Risk Management 02/2009; 5(1):79-84.