Genistein inhibits cardiac L-type Ca(2+) channel activity by a tyrosine kinase-independent mechanism.
It has been suggested that protein tyrosine kinase (PTK) activity can directly regulate cardiac L-type Ca(2+) channels. This conclusion is based to a large extent on the observation that the PTK inhibitor genistein can inhibit the cardiac L-type Ca(2+) current. The purpose of the present study was to determine whether the ability of genistein to inhibit cardiac L-type Ca(2+) channel activity is due to inhibition of PTK activity. Genistein significantly reduced the magnitude of the L-type Ca(2+) current in guinea pig ventricular myocytes recorded using the whole-cell patch-clamp technique. However, this effect was associated with extracellular, not intracellular, application of the drug. Peroxovanadate (PVN), a potent protein tyrosine phosphatase inhibitor, had no effect on the basal Ca(2+) current. PVN was also ineffective in preventing the inhibitory effect of genistein. Internal perfusion of cells with a pipette solution containing ATPgammaS was used to prevent reversibility of phosphorylation-dependent processes. This treatment did not alter the inhibitory effect of genistein, although it did result in irreversible protein kinase A-dependent regulation of the Ca(2+) current. Bath application of lavendustin A, a PTK inhibitor that is structurally unrelated to genistein, did not affect the Ca(2+) current amplitude. The inhibitory effect of genistein was also associated with a hyperpolarizing shift in the voltage dependence of Ca(2+) channel inactivation. These results are consistent with the conclusion that the cardiac L-type Ca(2+) current is not directly regulated by PTK activity and that the inhibitory effect of genistein is due to direct non-catalytic blockade of the channels.
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA.
Andriy E
AE
Belevych
Sunita
S
Warrier
Robert D
RD
Harvey
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology*; D004347:Drug Interactions; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology*; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism; D010636:Phenols / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D010636:Phenols; C069276:peroxovanadate; C022571:adenosine 5'-O-(3-thiotriphosphate); D014638:Vanadates; C062898:lavendustin A; D000255:Adenosine Triphosphate; D019833:Genistein; D011505:Protein-Tyrosine Kinases