Effects of extracellular potassium on ventricular automaticity and evidence for a pacemaker current in mammalian ventricular myocardium.
Automaticity was induced in isolated guinea pig and cat papillary muscles by application of depolarizing constant current pulses. Increasing extracellular potassium from 1 to 15 mM caused a shift of pacemaker-like activity to less negative diastolic potentials and a decrease in maximum phase 4 slope. Membrane resistance, estimated from the relation of applied current to maximum diastolic potential, decreased when extracellular potassium was increased. Voltage clamps of cat papillary muscle demonstrated that action potentials activate a time-dependent outward current which has a reversal potential of -79.1 mV (+/- 0.99 SE, n = 20) at an extracellular potassium concentration of 5 mM. The reversal potential of this current varies with extracellular K+ with a slope of 50-60 mV per 10-fold concentration change. The current is activated by voltage clamps or action potential plateaus in the range of -30 to +30 mV. It has a time constant of deactivation which increases from approximately 100 to over 400 msec as clamp potential is increased from -90 to -60 mV. It is proposed that this current is equivalent to Ix1 demonstrated in other cardiac tissues and is responsible, in combination with inward currents, for automaticity in ventricular fibers.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D004562:Electrocardiography; D006168:Guinea Pigs; D006329:Heart Conduction System / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008722:Methods; D009200:Myocardial Contraction / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology*; D013997:Time Factors; D016276:Ventricular Function
D011188:Potassium