Tyrosine kinase and phosphatase regulation of slow delayed-rectifier K+ current in guinea-pig ventricular myocytes.
The objective of this study was to investigate the involvement of tyrosine phosphorylation in the regulation of the cardiac slowly activating delayed-rectifier K(+) current (I(Ks)) that is important for action potential repolarization. Constitutive I(Ks) recorded from guinea-pig ventricular myocytes was suppressed by broad-spectrum tyrosine kinase (TK) inhibitors tyrphostin A23 (IC(50), 4.1+/-0.6 microm), tyrphostin A25 (IC(50), 12.1+/-2.1 microm) and genistein (IC(50), 64+/-4 microm), but was relatively insensitive to the inactive analogues tyrphostin A1, tyrphostin A63, daidzein and genistin. I(Ks) was unaffected by AG1478 (10 microm), an inhibitor of epidermal growth factor receptor TK, and was strongly suppressed by the Src TK inhibitor PP2 (10 microm) but not by the inactive analogue PP3 (10 microm). The results of experiments with forskolin, H89 and bisindolylmaleimide I indicate that the suppression of I(Ks) by TK inhibitors was not mediated via inhibition of (I(Ks)-stimulatory) protein kinases A and C. To evaluate whether the suppression was related to lowered tyrosine phosphorylation, myocytes were pretreated with TK inhibitors and then exposed to the phosphotyrosyl phosphatase inhibitor orthovanadate (1 mm). Orthovanadate almost completely reversed the suppression of I(Ks) induced by broad-spectrum TK inhibitors at concentrations around their IC(50) values. We conclude that basal I(Ks) is strongly dependent on tyrosine phosphorylation of Ks channel (or channel-regulatory) protein.
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
Sergey
S
Missan
Paul
P
Linsdell
Terence F
TF
McDonald
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000187:drug effects; D066298:In Vitro Techniques; D007529:Isoflavones / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology*; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D016276:Ventricular Function
D004791:Enzyme Inhibitors; D007529:Isoflavones; D024661:Potassium Channels, Inwardly Rectifying; C040641:genistin; D011505:Protein-Tyrosine Kinases; D017027:Protein Tyrosine Phosphatases