Voltage clamp hyperpolarization and depolarization of cardiac Purkinje fibers in sodium-free media rapidly induce potassium depletion and accumulation, altering ionic driving forces.
Voltage clamp hyperpolarization and depolarization result in currents consistent with depletion and accumulation of potassium in the extracellular clefts o cardiac Purkinje fibers exposed to sodium-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 cesium, changes in bathing media potassium concentration and osmolarity, and the behavior of membrane potential after hyperpolarizing pulses are all consistent with depletion of potassium upon hyperpolarization. A declining outward current was observed upon depolarization. Increasing the bathing media potassium concentration reduced the magnitude of this current. After voltage clamp depolarizations, membrane potential transiently became more positive. These findings suggest that accumulation of potassium 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.
Baumgarten et al. (Mon,) conducted a other in Cardiac Purkinje fibers in sodium-free solutions. Voltage clamp hyperpolarization and depolarization was evaluated on Potassium depletion and accumulation in extracellular clefts. Voltage clamp hyperpolarization and depolarization of cardiac Purkinje fibers in sodium-free media rapidly induce potassium depletion and accumulation, altering ionic driving forces.