Delayed rectifier K+ current in embryonic chick heart ventricle.
Single ventricular cells from 7- to 10-day-old embryonic chicks were studied with the use of whole cell, outside-out, and cell-attached patch-clamp techniques. The macroscopic delayed rectifier current, IK, activated at membrane potentials above -25 mV. Peak IK at +40 mV was 103 +/- 20 pA (5.7 +/- 1 microA/cm2). IK was selective for K ions with reversal potentials close to the Nernst equilibrium potentials. The onset of current during a voltage step was sigmoidal and was fit by the function IK = IKoo (1-e-t/tau)2. The peak time constant of activation was greater than 6 s at -25 mV (22 degrees C). Significant inactivation was not observed. IK was blocked by intracellular cesium, extracellular 1 mM 4-aminopyridine, 20 mM tetraethylammonium chloride, and 1 mM barium chloride. Single-channel recordings revealed a K+-selective channel with a slope conductance of 15 pS (extracellular [K+] = 4 mM, intracellular [K+] = 145 mM). An ensemble average of consecutive single-channel traces reproduced the whole cell current. The single-channel density was approximately 0.04/micron 2 based on frequency of patches containing the 15-pS single conductance. Approximately 100 channels/cell would sum to account for the net IK. We have described for the first time a channel underlying the main delayed rectifier current and, as such, a main repolarization current in chick ventricle.
Clapham
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Cardiovascular Division, Brigham and Women's Hospital, Boston, Massachusetts.
Logothetis
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D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D017609:Barium Compounds; D002586:Cesium / Q000494:pharmacology; D002642:Chick Embryo; D002712:Chlorides; D046508:Culture Techniques; D004594:Electrophysiology; D006321:Heart / Q000196:embryology* / Q000502:physiology; D011188:Potassium / Q000378:metabolism*; D012016:Reference Values; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D016276:Ventricular Function
D000631:Aminopyridines; D017609:Barium Compounds; D002712:Chlorides; D013757:Tetraethylammonium Compounds; C024986:barium chloride; D002586:Cesium; D001464:Barium; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D011188:Potassium