INHIBITORY EFFECTS OF CYPROHEPTADINE ON C ALMODULIN-ACTIVATED CA2-ATPASE ACTIVITY OF RABBIT ERYTHROCYTE-MEMBRANES()

Membranes prepared from rabbit erythrocyte hemolyzed in isosmotic imid azole (151 mmol . L-1, pH 7.4) buffer showed an enhancement of calmodu lin (CaM) activated Ca2+-ATPase activity compared with the membrane pr epared in hypotonic imidazole (10 mmol . L-1, EGTA 1 mmol . L-1, pH 7. 4) buffer. The Ca2+-ATPase activity of the former (activated-calmoduli n) was inhibited by cyproheptadine (Cyp) with lC5075 mumol.L-1(95% con fidence interval was 18-319 mumol.L-1, r=0.9118), while the Ca2+-ATPas a activity of the latter (inactivated) was hardly influenced. by Cyp. The results suggest that cyproheptadine antagonizes CaM, and its actio ns of the calcium antagonism and the anti-myocardial injury may, at le ast partially, be related to its CaM antagonism.