Na+Ca2+ exchange in squid optic nerve membrane vesicles is activated by internal calcium

Condrescu, Madalina; Gerardi, A; DiPolo, Reinaldo

doi:10.1016/0005-2736(88)90404-x

Biochimica et Biophysica Acta (BBA) - Biomembranes

1988

DOI: 10.1016/0005-2736(88)90404-x

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Na+Ca2+ exchange in squid optic nerve membrane vesicles is activated by internal calcium

Madalina Condrescu

A Gerardi

Reinaldo DiPolo

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Cited by 10 publications

(1 citation statement)

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“…Application of classical steady-state kinetic approaches (Cleland, 1963;Stein, 1986) to the Na+-Ca2+ exchange system has been seriously hampered due to the fact that in sarcolemmal and nerve membrane vesicles Ca¡ is accumulated, accelerating Na+-Ca2+ exchange (Reeves & Poronnik, 1987;Condrescu et al, 1988).…”

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confidence: 99%

Distinction between the two basic mechanisms of cation transport in the cardiac sodium-calcium exchange system

Khananshvili¹

1990

Biochemistry

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In order to distinguish between the Ping-Pong and sequential mechanisms of cation transport in the cardiac Na(+)-Ca2+ exchange system, the initial rates of the Nai-dependent 45Ca uptake (t = 1 s) were measured in reconstituted proteoliposomes, loaded with a Ca chelator. Under "zero-trans" conditions ([Na]o = [Ca]i = 0) at a fixed [Na]i = 10-160 mM with varying [45Ca]o = 2.5-122 microM for each [Na]i, the Km and Vmax values increased from 7.7 to 33.5 microM and from 2.3 to 9.0 nmol.mg-1.s-1, respectively. The Vmax/Km values show a +/- 2-10% deviation from the average value of 0.274 nmol.mg-1.s-1.microM-1 over the whole range of [Na]i. These deviations are within the standard error of Vmax (+/- 3-7%), Km (+/- 11-17%), and Vmax/Km (+/- 11-19%). This suggests that, under conditions in which Vmax and Km are [Na]i dependent and vary 4-5-fold, the Vmax/Km values are constant within the experimental error. In the presence of K(+)-valinomycin the Vmax/Km values are 0.85 +/- 0.17 and 1.08 +/- 0.18 nmol.mg-1.s-1.microM-1 at [Na]i = 20 and 160 mM, respectively, suggesting that under conditions of "short circuit" of the membrane potential the Vmax/Km values still exhibit the [Na]i independence. At a very low fixed [45Ca]o = 1.1 microM with varying [Na]i = 10-160 mM, the initial rates were found to be [Na]i independent. At a high fixed [45Ca]o = 92 microM the initial rates show a sigmoidal dependence on the [Na]i with Vmax = 13.8 nmol.mg-1.s-1, KmNa = 21 mM, and Hill coefficient nH = 1.5. The presented data support a Ping-Pong (consecutive) mechanism of cation transport in the Na(+)-Ca2+ exchanger.

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confidence: 99%

Distinction between the two basic mechanisms of cation transport in the cardiac sodium-calcium exchange system

Khananshvili¹

1990

Biochemistry

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In squid nerve fibers monovalent activating cations are not cotransported during Na+/Ca2+ exchange

Condrescu

Rojas

Gerardi

et al. 1990

Biochimica et Biophysica Acta (BBA) - Biomembranes

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Effect of Quin-2 on 45Ca2+ uptake mediated by Na+iCa2+o exchange and 45Ca2+ efflux in rat brain synaptosomes: a requirement for [Ca2+]i

Blanco¹,

Martínez‐Serrano²,

Bogónez³

et al. 1990

Cell Calcium

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Na+Ca2+ exchange in squid optic nerve membrane vesicles is activated by internal calcium

Cited by 10 publications

References 24 publications

Distinction between the two basic mechanisms of cation transport in the cardiac sodium-calcium exchange system

Distinction between the two basic mechanisms of cation transport in the cardiac sodium-calcium exchange system

In squid nerve fibers monovalent activating cations are not cotransported during Na+/Ca2+ exchange

Effect of Quin-2 on 45Ca2+ uptake mediated by Na+iCa2+o exchange and 45Ca2+ efflux in rat brain synaptosomes: a requirement for [Ca2+]i

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