Abstract
Summary The adenosinetriphosphatase activity of rat skeletal muscle membranes is inhibited about 45% by 5 × 10−4m quinidine sulfate and slightly (about 9%) by 5 × 10−5m quinidine sulfate. This enzymic activity requires sodium and magnesium. Higher concentrations of magnesium are inhibitory and the inhibitory effect of quinidine is decreased at high magnesium concentrations.