Abstract
The influence of ouabain and alpha angelica lactone on (45)calcium accumulation in cardiac microsomes was studied. Calcium binding (accumulation in the absence of excess oxalate or phosphate) was augmented by both ouabain and alpha angelica lactone in the presence of adenosine triphosphate (ATP) but unaffected in its absence. Calcium turnover (defined as the change in (45)Ca(++) bound to the microsomes after the specific activity is changed) was studied to determine if the augmented bound pool was freely exchangeable at equilibrium. Ouabain and alpha angelica lactone augmented calcium turnover in both the presence and absence of ATP. Calcium-stimulated ATPase was increased by both agents.It is proposed that these two unsaturated lactones, with known cardiotonic activity, may exert their effects by providing an increased contraction-dependent calcium pool to be released upon systolic depolarization.