Anion dependence of the contractions of skinned cardiac cells.

Cardiac muscle fragments with disrupted sarcolemmas were prepared by homogenization of mouse ventricles. The rate of spontaneous contractions was increased when a solution containing isobutyrate as the main anion was substituted with a solution rich in chloride. At low calcium concentrations preparations which were quiescent in the isobutyrate solution responded to the chloride with a strong single contraction.