title: Stimulation of calcium pump activity in heart sarcolemma by timolol.
abstract: The effects of beta-adrenergic blocking agents, timolol and atenolol (1-1000 microM), were studied on rat heart sarcolemmal ATPase and Ca2+ binding activities. Timolol, unlike atenolol, increased both Ca2+-stimulated ATPase and ATP-dependent Ca2+ binding; the maximal effects were seen at 1 microM concentration of timolol. Both timolol and atenolol did not alter the sarcolemmal Mg2+ ATPase and nonspecific Ca2+ binding activities. Sarcolemmal Ca2+-stimulated ATPase was also activated by concanavalin A (6-66 micrograms/mL) which is known to alter membrane fluidity; however, Mg2+ ATPase was unaffected by this agent. These results indicate that timolol may stimulate Ca2+ pump activity in heart sarcolemma by changing membrane fluidity in a manner similar to that of concanavalin A.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000032:analysis; D003208:Concanavalin A / Q000494:pharmacology; D003327:Coronary Disease / Q000378:metabolism; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D011412:Propanolamines / Q000494:pharmacology*; D051381:Rats; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism*; D013999:Timolol / Q000494:pharmacology*
chemical_list: D011412:Propanolamines; D003208:Concanavalin A; D013999:Timolol; D000252:Calcium-Transporting ATPases; D002118:Calcium