Evidence for a Calmodulin-Activated Ca 2+ Pump ATPase in Dog Erythrocytes

Abstract

Previous work in several laboratories revealed little or no Ca²⁺ pump ATPase activity and little or no activation of the ATPase by calmodulin (CaM) in membranes isolated from dog red blood cells (RBCs). In the present work, intact RBCs from dogs were exposed to the ionophore, A23187, in the presence of Ca²⁺. A rapid, apparently first order, loss of ATP occurred under these conditions. The first order rate constant was 0.0944 min^-1, or approximately 47% of that found in human RBCs under the same conditions. The anti-CaM drug, trifluoperazine, inhibited the loss of ATP and the Ca²⁺ activation curve of ATP loss in intact cells resembled that observed for CaM-activated Ca²⁺ pump ATPase in isolated human membranes. Taken together, these data are consistent with the interpretation that the dog RBC membrane contains a CaM-activated Ca²⁺ pump ATPase.