title: Osmotic modulation of slowly activating IKs in guinea-pig ventricular myocytes.
abstract: OBJECTIVE
  The aims of the study were to determine the effects of anisosmotic bathing solution on selected properties of I(Ks), the slowly activating delayed-rectifier K(+) current important for repolarization of the action potential in cardiac cells.
  
  
  RESULTS
  Guinea-pig ventricular myocytes were voltage-clamped using either the ruptured-patch or perforated-patch technique, and the amplitude, time course, and voltage dependence of I(Ks) were determined before [isosmotic (1T)] and during superfusion of hyposmotic (<1T) or hyperosmotic (>1T) bathing solution. Hyposmotic solution increased the amplitude of I(Ks), and hyperosmotic solution decreased it. Anisosmotic-induced changes in I(Ks) amplitude were complete in 2-5 min, well-maintained, reversible, and not accompanied by significant changes in I(Ks) time course and voltage dependence. There was little difference in the results obtained with the ruptured-patch technique and those obtained with the perforated-patch technique. The amplitude of I(Ks) was sensitive to small (±10%) changes in osmolarity, maximally increased by hyposmotic solution with T < 0.7, and strongly decreased by hyperosmotic solution with T > 1.5. Experimental data on a plot of relative (1T = 1.0) I(Ks) amplitude vs. the reciprocal of relative osmolarity are well-described by a Hill equation that has a lower asymptote of 0.0, an upper asymptote of 2.0, and a slope factor of 1.87 ± 0.07.
  
  
  CONCLUSIONS
  Modulation of I(Ks) amplitude by anisosmotic solution is independent of patch configuration, unaccompanied by changes in current gating, and well-described by a Hill dose-response relation that predicts relatively strong responses of I(Ks) to small perturbations in external osmolarity.
authors: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Sergey
authors: S
authors: Missan
authors: Lesya M
authors: LM
authors: Shuba
authors: Pavel
authors: P
authors: Zhabyeyev
authors: Terence F
authors: TF
authors: McDonald
mesh_terms: D000200:Action Potentials; D000818:Animals; D051668:Delayed Rectifier Potassium Channels / Q000378:metabolism*; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000378:metabolism*; D015640:Ion Channel Gating; D007700:Kinetics; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000378:metabolism*; D009997:Osmotic Pressure; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*
chemical_list: D051668:Delayed Rectifier Potassium Channels; D011188:Potassium