[Cationic specificity of a Ca2+-accumulating system in smooth muscle cell mitochondria].
In the experiments conducted with application of an isotopic technique (45Ca2+) on the myometrium cells suspension treated by digitonin solution (0.1 mg/ml) some properties of Ca ions accumulation system in the mitochondria--cationic and substrate specificity as well as effects of Mg2+ and some other bivalent metals ions on the Ca2+ accumulation velocity have been estimated. Ca ions accumulation from the incubation medium containing 3 mM sodium succinate Na, 2 mM Pi (as potassium K(+)-phosphate buffer, pH 7.4 at 37 degrees C), 0.01 mM (40CaCl2 + 45CaCl2) and 100 nM thapsigargin--selective inhibiting agent of endoplasmatic reticulum calcium pump were demonstrated as detected just only in presence of Mg, while not Ni, Co or Cu ions. The increase of Mg2+ concentration from 1 x 10(-6) to 10(-3) M induced the ATP dependent transport activation in the myometrium mitochondria. Under [Mg2+] increase till 40 mM this cation essentially decreased Ca2+ accumulation (by 65% from the maximal value). The optimum for Ca2+ transport in the myometrium cells suspension is Mg2+ 10 mM concentration. Ka activation apparent constant along Mg2+ value (in presence 3 mM ATP and 3 mM sodium succinate) is 4.27 mM. The above listed bivalent metals decreased Mg2+, ATP-dependent accumulation of calcium, values of inhibition apparent constants for ions Co2+, Ni2+ and Cu2+ were--2.9 x 10(-4) M, 5.1 x 10(-5) M and 4.2 x 10(-6) M respectively. For Mg2+, ATP-dependent Ca2+ transport in the uterus myocytes mitocondria a high substrate specificity is a characteristic phenomenon in elation to ATP: GTP, CTP and UTP practically fail to provide for Ca accumulation process.
Palladin Institute of Biochemistry, NAS of Ukraine, Kyiv.
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Veklich
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Kosterin
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Shynlova
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002413:Cations, Divalent; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D017136:Ion Transport; D007700:Kinetics; D008931:Mitochondria, Muscle / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism*; D009215:Myometrium / Q000378:metabolism*; D051381:Rats; D019284:Thapsigargin / Q000494:pharmacology
D002413:Cations, Divalent; D004791:Enzyme Inhibitors; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium