The effects of extracellular potassium, ouabain, and prostaglandins on intracellular potassium activity in sheep cardica Purkinje fibers.

(1) Intracellular K activity (aKi) of sheep heart Purkinje fibers was measured using K-selective microelectrodes (liquid ion exchanger). aKi in the resting state with an extracellular K of 4 mmol . l-1 EK was 112.9 +/- 6.1 mmol . l-1 (n = 47) for a membrane potential (VM) of -73.3 +/- 0.9 mV. VM deviated from the calculated potassium equilibrium potential (EK = -93mV). (2) When extracellular K was decreased to 2 mmol . l-1 or increased to 6 and 10 mmol . l-1 EK changed from -114 to -84 and -73 mV, with little change in aKi. (3) aKi and VM significantly decreased after administration of 10(-6) mol . l-1 ouabain. (4) Prostaglandins (PGI2 10-100 micrograms . l-1 and PGE2 0.01-1 microgram . l-1) decreased aKi without greatly changing VM. The differences between VM and EK became smaller. These effects indicate an increase in K permeability and may explain the antiarrhythmic action of prostaglandins.