Genistein elicits biphasic effects on L-type Ca2+ current in feline atrial myocytes.
A perforated patch recording method was used to determine the effects of genistein (Gen), a protein tyrosine kinase (PTK) inhibitor, on basal L-type Ca2+ current (ICa,L) in feline atrial myocytes. Gen (50 microM) elicited biphasic changes in ICa,L: an initial inhibition (-55 +/- 4%; phase 1) followed by a secondary stimulation (34 +/- 9%; phase 2) of ICa,L. Withdrawal of Gen elicited a further potentiation of ICa,L (152 +/- 19%; phase 3) above control (n = 46). In general, phase 1 inhibition and phase 3 potentiation varied directly with Gen concentration, and phase 2 stimulation exhibited biphasic concentration-dependent changes compared with control. When cells were dialyzed using a ruptured patch recording method, Gen elicited only inhibition of ICa,L; phases 2 and 3 were abolished. Vanadate (1 mM), an inhibitor of protein tyrosine phosphatase, abolished both Gen-induced inhibition and stimulation of ICa,L. Daidzein (50 microM), a weakly active analog of Gen, exerted no significant effects on ICa,L, and withdrawal of daidzein failed to potentiate ICa,L. In a few cells, Gen elicited a prominent vanadate-sensitive stimulation of ICa,L in the absence of any significant inhibition of ICa,L. Gen-induced changes in ICa,L were unaffected by either 100 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-acetoxymethyl ester (AM) or 1 microM ryanodine, agents that alter intracellular Ca2+; 4 microM H-89 or 50 microM Rp diastereomer of adenosine 3',5'-monophosphothioate (RP-cAMPS), inhibitors of protein kinase A (PKA); 0.1 microM calphostin C or 2 microM chelerythrine, inhibitors of protein kinase C (PKC); or 100 microM NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide (NO) synthase. We conclude that in feline atrial myocytes, Gen acts via membrane-bound PTKs to inhibit ICa,L and via cytosolic PTKs to stimulate ICa,L. Gen-induced changes in ICa,L are not related to changes in intracellular Ca2+ or to secondary interactions with either PKA, PKC, or NO signaling pathways. These results indicate that in atrial myocytes ICa,L is regulated by two independent and competing PTK signaling mechanisms.
Wang
Y G
YG
Department of Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois 60153, USA.
Lipsius
S L
SL
D000470:Alkaloids; D000818:Animals; D053119:Benzophenanthridines; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002415:Cats; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D019833:Genistein / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006325:Heart Atria; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000166:cytology; D010617:Phenanthridines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D012433:Ryanodine / Q000494:pharmacology; D013449:Sulfonamides; D013873:Thionucleotides / Q000494:pharmacology; D019323:omega-N-Methylarginine / Q000494:pharmacology
D000470:Alkaloids; D053119:Benzophenanthridines; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D010617:Phenanthridines; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D013873:Thionucleotides; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D012433:Ryanodine; C016957:adenosine-3',5'-cyclic phosphorothioate; D019323:omega-N-Methylarginine; D004533:Egtazic Acid; D019833:Genistein; D000242:Cyclic AMP; C016299:chelerythrine; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide