The resting potential in heart muscle.
The resting potential in heart muscle is largely a K+ diffusion potential as predicted by Bernstein. However, deviations from the Nernst equation are reported which could be the result of different intracellular and extracellular activity coefficients, errors in measurement of intracellular K+, partial permeabilities to other ions, or electrogenic pumps. The origin of the cardiac resting potential was investigated by use of K+- and Na+-selective microelectrodes during exposure of ventricular muscle and Purkinje fibers to various solutions. The intracellular activity coefficient for K+ was apparently less than the extracellular one, and membrane potential in ventricular muscle followed the K+ activity gradient for extracellular K+ of 10 mM or more. In Purkinje fibers, the resting potential correlated directly with intracellular K+ activity and inversely with intracellular Na+ activity. At normal and low extracellular K+, there is a substantial Na+ leakage and some Ca2+ leakage. No contribution of electrogenic pumps or extracellular K+ accumulation could be found in the steady resting state.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability; D004562:Electrocardiography; D007473:Ion Channels / Q000502:physiology*; D009200:Myocardial Contraction; D011188:Potassium / Q000378:metabolism; D011690:Purkinje Fibers / Q000502:physiology; D012756:Sheep; D012964:Sodium / Q000378:metabolism; D016276:Ventricular Function
D007473:Ion Channels; D012964:Sodium; D011188:Potassium; D002118:Calcium