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1987•Acta chemica Scandinavica/Acta chemica Scandinavica. B, Organic chemistry and biochemistry/Acta chemica Scandinavica. A, Physical and inorganic chemistry/Acta chemica Scandinavica. Series B. Organic chemistry and biochemistry/Acta chemica Scandinavica. Series A, Physical and inorganic chemistryOpen access

Non-respiring Rat Liver Mitochondria Do Not Have a Ca2+/2H+ Antiporter.

Nils-Erik Leo Saris, Margareta Baltscheffsky, Margareta Baltscheffsky, Gunnar Öquist, Petter Gustafsson

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Abstract

Liver mitochondria take up Ca2+ by the Ca2+ uniporter, whereas at steady state efflux is believed to occur mainly by means of a ruthenium red-insensitive Ca2+/2H+ antiporter. The latter activity was studied in respiration-inhibited mitochondria in the presence of ruthenium red and was measured as Ca2+ uptake following acidification of the matrix by addition of nigericin, which catalyzes K+/H+ exchange. Ca2+ uptake was stimulated by protonophorous uncoupling agents and inhibited by increasing the concentration of ruthenium red. However, the rates were always smaller than those obtained by addition of valinomycin instead of nigericin. This indicates that under these conditions, Ca2+ fluxes are not mediated by a Ca2+/2H+ antiporter but by residual uniporter activity.

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Liver mitochondria take up Ca2+ by the Ca2+ uniporter, whereas at steady state efflux is believed to occur mainly by means of a ruthenium red-insensitive Ca2+/2H+ antiporter. The latter activity was studied in respiration-inhibited mitochondria in the presence of ruthenium red and was measured as Ca2+ uptake following acidification of the matrix by addition of nigericin, which catalyzes K+/H+ exchange. Ca2+ uptake was stimulated by protonophorous uncoupling agents and inhibited by increasing the concentration of ruthenium red. However, the rates were always smaller than those obtained by addition of valinomycin instead of nigericin. This indicates that under these conditions, Ca2+ fluxes are not mediated by a Ca2+/2H+ antiporter but by residual uniporter activity.

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Available abstract

Liver mitochondria take up Ca2+ by the Ca2+ uniporter, whereas at steady state efflux is believed to occur mainly by means of a ruthenium red-insensitive Ca2+/2H+ antiporter. The latter activity was studied in respiration-inhibited mitochondria in the presence of ruthenium red and was measured as Ca2+ uptake following acidification of the matrix by addition of nigericin, which catalyzes K+/H+ exchange. Ca2+ uptake was stimulated by protonophorous uncoupling agents and inhibited by increasing the concentration of ruthenium red. However, the rates were always smaller than those obtained by addition of valinomycin instead of nigericin. This indicates that under these conditions, Ca2+ fluxes are not mediated by a Ca2+/2H+ antiporter but by residual uniporter activity.

Key concepts: Nigericin, Antiporter, Ruthenium red, Uniporter, Chemistry, Valinomycin, Mitochondrion, Biophysics

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