Binding of cardioglobulin-C-Ca⁴⁵ to cardiac muscle and release by cardioglobulin-A

¹ Laboratory of Kidney and Electrolyte Metabolism, National Heart Institute, National Institutes of Health, Bethesda, Maryland

The cardiotonic action of cardioglobulin on the frog heart is a result of the interaction of three globulins, cardioglobulin-A, -B, and -C. Cardioglobulin-B binds to the heart. It has been shown that cardioglobulin-C binds to a cardioglobulin-B heart, but not to a heart without cardioglobulin-B. Cardioglobulin-C binding has been demonstrated both by biological activity and by persistence of cardioglobulin-C-Ca⁴⁵ counts on the heart. The addition of cardioglobulin-A to a cardioglobulin-B-C heart causes the characteristic cardiotonic action of the system. Addition of cardioglobulin-A is associated with release of tracer from bound cardioglobulin-C-Ca⁴⁵, measured as a decrease in heart radioactivity. The correlations between biological activity and localization of Ca⁴⁵ of labeled cardioglobulin-C are consistent with the hypothesis that cardioglobulin action is associated with the release of cardioglobulin-C calcium into the cell. The amount of calcium involved has been estimated to be of the order of 10^–4 µm for an 80-mg frog heart.

Key Words: cardioglobulin • protein • heart • calcium • cell membrane • transport • isotope

Submitted on December 9, 1964