Depletion and accumulation of potassium in the extracellular clefts of cardiac Purkinje fibers during voltage clamp hyperpolarization and depolarization: experiments in sodium-free bathing media.

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Abstract
Voltage clamp hyperpolarization and depolarization result in currents consistent with depletion and accumulation of K in the extracellular clefts of cardiac Purkinje fibers [from sheep] exposed to Na-free solutions. Upon hyperpolarization, an inward current that decreased with time (id) was observed. The time course of tail currents could not be explained by a conductance exhibiting voltage-dependent kinetics. The effect of exposure to Ce, changes in bathing media K concentration and osmolarity, and the behavior of membrane potential after hyperpolarizing pulses are all consistent with depletion of K upon hyperpolarization. A declining outward current was observed upon depolarization. Increasing the bathing media K concentration reduced the magnitude of this current. After voltage clamp depolarizations, membrane potential transiently became more positive. K accumulation apparently occurs upon depolarization. The results indicate that changes in ionic driving force may be easily and rapidly induced. Consequently, conclusions based on the assumption that driving force remains constant during the course of a voltage step may be in error.