Distribution of potassium, sodium, and chloride in canine Purkinje and ventricular tissues. Relation to cellular potential.

Cellular resting and action potentials and total tissue concentrations of K + , Na + , and Ch were measured in canine myocardial and Purkinje tissues. The results with myocardium were consistent with those of others: the total tissue concentration of K was greater than that of Na of Ch. In Purkinje tissue, the total tissue concentration of K was relatively low, while that of Na and of Ch was high. Extracellular space was calculated on the basis of four different assumptions about the intracellular concentration of one of the ions: (1) the intracellular concentrations of Ch is zero; (2) the electrochemical equilibrium potential of Ch equals the cellular resting potential; (3) the electrochemical equilibrium potential of K equals the cellular maximum diastolic potential; (4) the electrochemical equilibrium potential of Na equals the reversal of the cellular action potential. In the myocardium, the lowest estimate of extracellular space was 14 ± 2%, and the highest was 18 ± 2%. In the Purkinje tissue, the minimum extracellular space: (1) permitting adequate intracellular K to account for the maximum diastolic potential was 45 ± 3%; (2) consistent with passive distribution of Ch was 61 ± 4%; (3) yielding low enough intracellular concentration of Na to account for the reversal of the action potential was 63 ± 10%. These results suggest that in cardiac Purkinje tissue: (1) the extracellular space is unusually large with respect to that of myocardium and skeletal muscle; (2) intracellular activities of ions do not necessarily equal concentrations; or (3) intracellular space is not necessarily a single compartment. ADDITIONAL