Electrochemical potentials of potassium in skeletal muscle under different metabolic states

Abstract

Intracellular potassium and membrane potential were measured simultaneously by means of double-barrelled liquid ion-exchange microelectrodes in single fibers of rat thigh muscle in vivo in rats maintained in seven different metabolic states. The K+ equilibrium potential (EK) was more negative than the simultaneously measured membrane potential (Em) in the normal state by 18.4 mV. K+ loading, acute and chronic, resulted in depolarization of Em due to increased serum K+ (hyperkalemia) with no increase in intracellular K+. K+ depletion resulted in hyperpolarization of Em 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.

Distribution of lactate and other ions in inactive skeletal muscle: influence of hyperkalemic lactacidosis

“…The calculated values for both variables are within the range reported by Khuri et al (1992) in rat thigh muscles, as measured using double-barreled intracellular microelectrodes. Also, the calculated decreases in E m (see Table 5) in response to LP are also in agreement with the 10-mV decrease in E m in response to a 2.5 mM elevation in plasma [K + ] (Khuri et al1992).…”

“…It was also assumed that the altered perfusate composition did not affect the proportionality among sarcolemmal ion conductances, i.e., ion permeability coefficients. It is expected, in resting skeletal muscle, that relative ion permeabilities were not sufficiently influenced (see Khuri et al 1992) to alter the interpretation of the calculated E m data.…”

Relationship of Muscle Strength to Potassium Concentration in a Hypokalaemic Infant

“…Work on in vivo muscle shows hyperpolarization, decreased excitability and weakness in response to hypokalaemia 7 , while studies of other myopathies induced by hypokalaemia show direct muscle involvement 8,9 . The exact pathophysiology of hypokalaemiainduced skeletal muscle weakness remains uncertain 10 ; however, reduced frequency and duration of muscle contraction is probably the main cause 11 .…”