Missan Sergey, Linsdell Paul, McDonald Terence F
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Pflugers Arch. 2008 Jun;456(3):489-500. doi: 10.1007/s00424-007-0424-y. Epub 2007 Dec 21.
The objective of this study was to investigate the involvement of tyrosine phosphorylation in the hyposmotic stimulation of cardiac I Ks, a slowly activating delayed-rectifier K+ current that promotes repolarization of the action potential. The current was recorded from whole-cell-configured guinea-pig ventricular myocytes before, during, and after their exposure to solution whose osmolarity was 0.75 times normal. Exposure to hyposmotic solution caused a near-doubling of the amplitude of I Ks, with little change in the voltage dependence of current activation. Stable, hyposmotically stimulated I Ks (I Ks,Hypo) was decreased by broadspectrum tyrosine kinase (TK) inhibitors tyrphostin A23 (IC50 approximately 5 microM) and tyrphostin A25 (IC50 15.8 +/- 1.6 microM) but not by TK-inactive tyrphostin analogs, suggesting that tyrosine phosphorylation is important for maintenance of the current. In agreement with that view, we found that the TK-inhibitor action on I Ks,Hypo was strongly antagonized by vanadate compounds known to inhibit phosphotyrosyl phosphatase. When myocytes were pretreated with TK inhibitors, the stimulation of I Ks was attenuated in a concentration-dependent manner. The attenuation was not due to concomitant attenuation of a stimulation of tyrosine phosphorylation because neither the stimulation of I Ks nor its rate of decay following removal of hyposmotic solution was affected by pretreatment with vanadates. We suggest that the stimulation of I Ks by hyposmotic solution is dependent on a basal tyrosine phosphorylation that modulates a swelling-induced I Ks-stimulatory signal and/or the receptivity of Ks channels to that signal.
本研究的目的是调查酪氨酸磷酸化在心脏I Ks的低渗刺激中的作用，I Ks是一种缓慢激活的延迟整流钾电流，可促进动作电位的复极化。在豚鼠心室肌细胞暴露于渗透压为正常0.75倍的溶液之前、期间和之后，从全细胞模式记录该电流。暴露于低渗溶液导致I Ks的幅度几乎翻倍，而电流激活的电压依赖性变化很小。广谱酪氨酸激酶（TK）抑制剂 tyrphostin A23（IC50约为5 microM）和tyrphostin A25（IC50为15.8 +/- 1.6 microM）可降低稳定的、低渗刺激的I Ks（I Ks,Hypo），但TK无活性的tyrphostin类似物则无此作用，这表明酪氨酸磷酸化对于维持该电流很重要。与该观点一致，我们发现钒酸盐化合物（已知可抑制磷酸酪氨酸磷酸酶）可强烈拮抗TK抑制剂对I Ks,Hypo的作用。当用TK抑制剂预处理心肌细胞时，I Ks的刺激以浓度依赖性方式减弱。这种减弱不是由于酪氨酸磷酸化刺激的同时减弱，因为钒酸盐预处理既不影响I Ks的刺激，也不影响去除低渗溶液后其衰减速率。我们认为，低渗溶液对I Ks的刺激依赖于基础酪氨酸磷酸化，该磷酸化调节肿胀诱导的I Ks刺激信号和/或Ks通道对该信号的反应性。
