Spermine modulates calcium flux through the rat erythrocyte membrane

The uptake of 45Ca by inside-out erythrocyte membrane vesicles (IOV) was dose-dependently inhibited by spermine. A cationic substance, Mg2+, did not affect this inhibitory activity of spermine. Ca(2+)-ATPase activity, however, was not inhibited by spermine at a concentration that could inhibit the uptake of 45Ca by the IOV. The release of 45Ca from IOV was significantly accelerated by spermine. Spermine bound to the surface of the IOV and was removed by treatment with acetic acid. These results suggest that spermine stimulates the release of Ca2+ from the IOV (or uptake of Ca2+ by erythrocytes) via an effect on the outer surface of the IOV (or the inner surface of erythrocytes).