Inhibition of calmodulin-activated Ca2+-ATPase by propranolol and nadolol.

Propranolol, at concentrations ranging from 0.05 to 0.5 mM, inhibits the calmodulin-activated Ca2+-ATPase of human erythrocyte membranes. In the same concentration range it is without effect on the basal Ca2+-ATPase. The inhibition is competitive and appears to be due to membrane binding, rather than to combination with cytoplasmic calmodulin as is the case for phenothiazines. This effect of propranolol may explain its ability to open the calcium-gated potassium channel, and could also be related to its action as a beta-adrenergic blocker. Nadolol, another beta-adrenergic blocker, is also an inhibitor of calmodulin-activated Ca2+-ATPase.