Permeability of time-dependent K+ channel in guinea pig ventricular myocytes to Cs+, Na+, NH4+, and Rb+.
Currents through time-dependent K+ channels (also referred to as IK or the delayed rectifier) were studied with the whole cell patch-clamp technique in isolated guinea pig ventricular myocytes. IK measurements were restricted to the examination of deactivation tail currents. Substitution of various monovalent cations for external K+ produced shifts of the reversal potential of IK. These shifts were used to calculate permeability ratios relative to K+. The permeability sequence for the IK channels was K+ = Rb+ greater than NH4+ = Cs+ greater than Na+. Time-dependent outward currents were also examined when the myocytes were dialyzed with Cs+ instead of K+. A sizeable time-dependent outward current, quite similar to that seen with K+ dialysis, was demonstrated. This current was primarily carried by intracellular Cs+, as the reversal potential of the current shifted 46 mV per 10-fold change of external Cs+ concentration. The significance of Cs+ permeation through IK channels is discussed with respect to the common use of Cs+ in isolating other currents.
Hadley
R W
RW
Department of Physiology, School of Medicine, University of Maryland, Baltimore 21201.
Hume
J R
JR
D000641:Ammonia / Q000493:pharmacokinetics; D000818:Animals; D002414:Cations, Monovalent / Q000493:pharmacokinetics*; D002586:Cesium / Q000493:pharmacokinetics; D006168:Guinea Pigs; D006352:Heart Ventricles; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010539:Permeability; D015221:Potassium Channels / Q000378:metabolism*; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000493:pharmacokinetics; D013997:Time Factors
D002414:Cations, Monovalent; D015221:Potassium Channels; D002586:Cesium; D000641:Ammonia; D012964:Sodium; D012413:Rubidium