Effect of cold on muscle potentials and electrolytes

Abstract

External cooling in vivo produces multiple changes in human and rat muscle membrane potentials and electrolytes. The first change noted is the appearance of increasing numbers of spontaneous potentials and repetitive action potentials after a single stimulus as the rat muscle is cooled to 32° C or less. Extracellular action potentials in humans and both intracellular and extracellular action potentials in rats become progressively more prolonged as the muscle cools below 26° C. In the animals this is accompanied by an increase in muscle Na (and Cl) and decrease in muscle K. Further cooling to below 23° C produces a drop in resting membrane potential as well as progressive increase in duration of the action potential. The previous increase in muscle Na is unaffected but muscle K decreases progressively and muscle water increases without change in muscle inulin space. Muscle Mg and Ca were not significantly different from control values. As cooling progresses in both rats and humans there is at first a slight increase in amplitude of the action potential and then a marked and significant diminution in amplitude. Cooling increases the threshold for stimulation and the delay between stimulus and onset of action potential. At temperatures below 8° C no visible contraction could be seen and the membrane became unresponsive to stimuli of greater than 100 v. The repetitive action potentials noted with minimal cooling diminished rapidly in amplitude. Repetitive action potentials became undemonstrable before the single stimulated action potential did. The possible interrelation of electrolyte changes, muscle membrane potentials and muscle contraction is considered.