[Effect of sodium gradient on calcium uptake by plasma membranes of the myometrium].
The effects of sodium gradient on Ca2+ uptake by plasma membranes of the myometrium were studied. It was found that the changes in the composition of the incubation mixture reduce 45Ca2+ uptake by Na+-loaded vesicles in the following order: sucrose greater than Li+ greater than K+ greater than Na+. The ratio of 45Ca2+ uptake by Na+-loaded vesicles in a KCl-containing medium, i. e. Nai/Ke, to the 45Ca2+ uptake by Na+-loaded vesicles in a NaCl-containing medium (Nai/Nae) or by K+-loaded vesicles in a KCl-containing medium (Ki/Ke) is 1.9 and 1.3, respectively. NaCl (100 mM) in the presence of 1 mM EGTA stimulates the release of 45Ca2+ accumulated in the course of the ATP-dependent process much stronger than does KCl taken at the same concentration. The plots for the dependence of the rate of 45Ca2+ influx into the vesicles on [Nai+] and [Cae2+] are characterized by a plateau. LaCl3 (0.1 mM) added to the Na+-loaded vesicles after their 5 min incubation with 45Ca2+ and KCl decreases the calcium uptake down to 70%; when the Na+-loaded vesicles are incubated in a medium wit NaCl and 45Ca2+ this uptake is decreased down to 50%. Studies on the ionophore A-23187 and Na-DS demonstrated that no 45Ca2+ influx into the vesicles stimulated by sodium gradient occurs against the electrochemical potential gradient. The role of sodium gradient in Ca2+ transport in myometrium cells is discussed.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002414:Cations, Monovalent; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005260:Female; D007700:Kinetics; D009215:Myometrium / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D014599:Uterus / Q000378:metabolism*
D002414:Cations, Monovalent; D012967:Sodium Dodecyl Sulfate; D000001:Calcimycin; D012964:Sodium; D002118:Calcium
Vliianie gradienta natriia na pogloshchenie kal'tsiia vo fraktsii plazmaticheskikh membran miometriia.