THE ORIGIN OF SPONTANEOUS CONTRACTIONS AND CHANGES IN NEUROMUSCULAR TRANSMISSION IN BARIUM-TREATED MUSCLE

Abstract

Among alkali-earth ions, barium is specific in causing some excitable cells to produce an action potential resembling that of cardiac muscle either in the presence or absence of external sodium ions. Fatt and Ginsborg showed that in crustacean muscle fibers kept in barium solution the amplitude of the action potential depends on the barium concentration, and they concluded that an influx of barium ions could account for the observed action potentials. Our recent experiments on bariumtreated amphibian neuron soma has led to the same conclusion.Another characteristic action of barium is a marked stimulation of muscle of all types. Muscles display vigorous contractions under the presence of barium ions. In contrast, other alkali-earth ions have no such stimulating action, and calcium in particular has stabilizing action although its ionic nature resembles barium ion. The primary purpose of this study is to clarify the origin of spontaneous contractions in barium-treated amphibian skeletal muscle. The antagonism between barium and calcium actions on the muscle and the influence of barium on neuromuscular transmission have also been investigated.