Ouabain contracture of frog heart: Ca45 movements and effect of EDTA

Abstract

Ethylenediaminetetraacetic acid (EDTA) renders frog heart muscle fibers indiscriminately permeable to Na, K and S³⁵O₄ and causes relaxation of contractures induced by ouabain but has no effect on contractures induced by iodoacetate. The contracture induced by iodoacetate under anaerobic conditions can be reversed aerobically either in the presence or absence of EDTA. These observations indicate that the ouabain contracture is not due primarily to an intracellular shift in Na⁺ or K⁺ concentration nor to a gross interference with intracellular energy metabolism but could be due to an altered handling of Ca⁺⁺ by the ouabain-treated muscle. A slightly greater than normal uptake of perfusate Ca⁴⁵ was found to occur during ouabain contracture but not during exposure to concentrations of the drug causing only positive inotropic effects.