title: Involvement of tyrosine kinase in the hyposmotic stimulation of I Ks in guinea-pig ventricular myocytes.
abstract: 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.
authors: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Sergey
authors: S
authors: Missan
authors: Paul
authors: P
authors: Linsdell
authors: Terence F
authors: TF
authors: McDonald
mesh_terms: D000200:Action Potentials; D000818:Animals; D048429:Cell Size; D051668:Delayed Rectifier Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066246:ErbB Receptors / Q000378:metabolism; D019833:Genistein / Q000494:pharmacology; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000201:enzymology; D066298:In Vitro Techniques; D007700:Kinetics; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D009997:Osmotic Pressure; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D011799:Quinazolines; D015398:Signal Transduction / Q000187:drug effects; D020032:Tyrphostins / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: C412373:AG 1879; D051668:Delayed Rectifier Potassium Channels; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D011799:Quinazolines; D020032:Tyrphostins; C402001:bis(N,N-dimethylhydroxamido)hydroxooxovanadate; C079836:tyrphostin 25; C101044:RTKI cpd; D014638:Vanadates; D019833:Genistein; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D019061:src-Family Kinases; D017027:Protein Tyrosine Phosphatases; C060641:tyrphostin A23