title: [Effect of cardenolids and sodium ion gradient on ATP-dependent Ca2+ accumulation in cardiac sarcolemmal vesicles].
abstract: Sarcolemmal preparations isolated from rat and guinea pig hearts mostly consisting of inside-out membrane vesicles catalyzed ATP-dependent Ca2+ accumulation. The creatine kinase ATP-regenerating system containing exogenous creatine kinase and phosphocreatine was most effective in supporting Ca2+ accumulation. The normalized rate of Ca2+ accumulation obtained by dividing the Ca2+ uptake rate by its initial equilibrium vesicular content was correlated with the (Na+ K+)-ATPase activity. The ATP-dependent Ca2+ uptake in sarcolemmal vesicles was inhibited by cardenolids--digitoxigenin and ouabain (40-50%), when the latter acted from inside the vesicles. The Ca2+ gradient formed in sarcolemmal vesicles at the expense of ATP was dissipated by Na+ but not by Li+ added into the external medium. The external sodium ions also caused Ca2+ efflux from sarcolemmal vesicles equilibrated with Ca2+. The described effects of Na+ are taken to show the existence of a Na-Ca exchange system in cardiac sarcolemma. Ca2+-ATPase of sarcoplasmic reticulum (SR) vesicles from guinea pig heart as well as ATP-dependent Ca2+ influx in these preparations were found to be partially suppressed by digitoxigenin. External NaCl led to be a rapid (during 5-10 sec) fall in vesicular Ca2+ content (by about 40%) accumulated at the expense of ATP followed by a return of Ca2+ content to its initial level. LiCl had no effect on Ca2+ content in SR. NaCl gradient directed inside the SR vesicles did not influence the distribution of Ca2+ between internal and external vesicular volumes in equilibrium (without ATP). The differences in properties of the Ca-pump of sarcolemma and sarcoplasmic reticulum found in this work support the idea on the existence of sarcolemmal system of ATP-dependent transport of Ca2+.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002298:Cardenolides / Q000494:pharmacology*; D003402:Creatine Kinase / Q000378:metabolism; D006168:Guinea Pigs; D008094:Lithium / Q000494:pharmacology; D009206:Myocardium / Q000201:enzymology*; D051381:Rats; D012508:Sarcolemma / Q000187:drug effects / Q000201:enzymology*; D012964:Sodium / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D002298:Cardenolides; D008094:Lithium; D012964:Sodium; D003402:Creatine Kinase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium
vernacular_title: Vliianie kardenolidov i gradienta Na+ na ATP-zavisimoe nakoplenie Ca2+ preparatemi sarkolemmy iz miokarda.