title: Membrane permeability during low potassium depolarization in sheep cardiac Purkinje fibers.
abstract: Exposure of sheep Purkinje fibers to low [K]o leads to marked depolarization to a stable potential of about -40 mV. This level is equivalent to the plateau of the Purkinje fiber action potential. The low [K]o depolarization could be prevented by removal of [Na]o and was modified by tetrodotoxin. The membrane potential in the depolarized state was unresponsive to changes in [Cl]o or [Ca]o and it was poorly responsive to changes in [K]o between 0 and 2 mM. Repolarization was induced by decrease in [Na]o with a slope response of 30 mV/10-fold change in [Na]o. Average internal K activity (aK) in the resting state with a [K]o of 5 mM was 121.4 mM for a membrane potential of -80 mV. During low K depolarization aK was 119.7 mM with a membrane potential of -34 mV. The depolarization was therefore due to a change in membrane permeability, with little change in aK. Upon restoration of [K]o the fiber repolarized to values transiently more negative than the prior resting potential. These transient potentials were more negative than the K equilibrium potential (VK), if it is calculated assuming a uniform [K]o. The hyperpolarization was reduced by ouabain [10(-6)] or by low [Ca]o.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000494:pharmacology; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000494:pharmacology; D006329:Heart Conduction System / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D011690:Purkinje Fibers / Q000378:metabolism* / Q000502:physiology; D012756:Sheep / Q000502:physiology; D012964:Sodium / Q000494:pharmacology
chemical_list: D002712:Chlorides; D012964:Sodium; D011188:Potassium; D002118:Calcium