Mechanisms of changes in K+ balance on reduction and reestablishment of flow in isolated rat liver

Abstract

The effects of low flow and reestablished normal flow on K+ balance and carboxylic acid balance was studied in perfused liver of 48-h starved rats at perfusate pH 7.4 and 6.8. The rate of net K+ release induced by ouabain was 1.8 mumol.min-1.g-1 at pH 7.4 and 1.4 mumol.min-1.g-1 at pH 6.8. Lowering of flow to 30% normal was accompanied by a transient, diphasic loss of K+ (max 0.15 mumol.min-1.g-1). Reestablished normal flow was immediately accompanied by a monophasic K+ uptake (max 0.35 mumol.min-1.g-1). These changes in potassium balance were independent of perfusate pH. Reduction of flow caused an almost immediate depolarization of 4 mV followed by a steady tendency to repolarization. Reestablished normal flow induced a transient hyperpolarization. Production of carboxylic acids during the low flow period did not correlate with the diphasic time course of K+ loss, and carboxylic acid uptake after reestablishment of flow did not correlate with the transient uptake of K+. The data show that the initial phase of K+ loss during low flow is due to inhibition of the Na(+)-K(+)-pump; the second phase may be reasonably explained by increased K+ permeability concomitant to cellular volume regulation.