Tyrosine kinase and phosphatase regulation of slow delayed-rectifier K+ current in guinea-pig ventricular myocytes |
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Authors: | Sergey Missan Paul Linsdell Terence F McDonald |
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Institution: | Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7 |
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Abstract: | 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 (IC50, 4.1 ± 0.6 μ m ), tyrphostin A25 (IC50, 12.1 ± 2.1 μ m ) and genistein (IC50, 64 ± 4 μ m ), but was relatively insensitive to the inactive analogues tyrphostin A1, tyrphostin A63, daidzein and genistin. I Ks was unaffected by AG1478 (10 μ m ), an inhibitor of epidermal growth factor receptor TK, and was strongly suppressed by the Src TK inhibitor PP2 (10 μ m ) but not by the inactive analogue PP3 (10 μ m ). 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 m m ). Orthovanadate almost completely reversed the suppression of I Ks induced by broad-spectrum TK inhibitors at concentrations around their IC50 values. We conclude that basal I Ks is strongly dependent on tyrosine phosphorylation of Ks channel (or channel-regulatory) protein. |
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