Abstract
Intracellular potassium and membrane potential were measured simultaneously by means of doubleโbarrelled liquid ionโexchange microelectrodes in single fibers of rat thigh muscle in vivo in rats maintained in seven different metabolic states. The K^+^ equilibrium potential (E~k~) was more negative than the simulataneously measured membrane potential (E~m~) in the normal state by 18.4 mV. K^+^ loading, acute and chronic, resulted in depolarization of E~m~ due to increased serum K^+^ (hyperkalemia) with no increase in intracellular K^+^. K^+^ depletion resulted in hyperpolarization of E~m~ as plasma K^+^ decreased proportionately more than intracellular K^+^. Low Na^+^ diet had no effect. Intracellular K^+^ was decreased in acute acidosis but not in the chronic state. Thus K^+^ depletion and acute acidosis are associated with intracellular K^+^ decrease. The fact that hyperpolarization exists in the former and not the latter is a reflection that hypokalemia accompanies the former condition. The hyperpolarizing states of K^+^ depletion and chronic acidosis are accompanied by decreased excitability and muscle weakness. ยฉ 1992 WileyโLiss, Inc.