Depolarization of frog muscle by low temperatures and by chloride-free solutions

Abstract

Isethionate is an anion with a low permeability in frog muscle fibers. When a muscle is immersed in a Ringer solution in which most of the Cl- is replaced by isethionate, some of the fibers are spontaneously active. During cooling the muscle fibers depolarize and fire action potentials repetitively. A large contraction is associated with the repetitive firing. Treatments that prevent spontaneous electrical activity also abolish the cold induced contractions. Cold also causes a depolarization in muscles immersed in Cl Ringer solution; the initial depolarization is greater than the value calculated from steady-state equations. The size of this transient depolarization is not modified by reducing [Na]o or by equilibrating the muscle in a solution that is known to reduce markedly [Na]i and [Cl]i.