Factors affecting contraction and relaxation in dog glycerinated cardiac fibers

Abstract

Factors affecting contraction and relaxation were studied in dog cardiac muscle fibers which were extracted in 50% glycerol for varying periods of time. It was found that in fibers extracted for short periods of time, Ca, Mg, and ATP were necessary for contraction, but as fibers were extracted for longer periods they gradually lost their Ca dependency. High concentrations of ATP and Mg produced relaxation in fresh fibers, but not in fibers extracted for long periods. Ca inhibited this relaxation. Creatine phosphate produced relaxation similar to that produced by high ATP concentrations (13mM). Ouabain had no effect on contraction or relaxation in the presence or absence of ethylenebis (oxyethylenenitrilo) tetraacetic acid.