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  • Title: [Effect of sodium gradient on calcium uptake by plasma membranes of the myometrium].
    Author: Bratkova NF, Kurskii MD, Kosterin SA.
    Journal: Biokhimiia; 1982 Jun; 47(6):1015-21. PubMed ID: 6810956.
    Abstract:
    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.
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