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ΔpH Induced Calcium Fluxes in Rat Liver Mitochondria

1979; Wiley; Volume: 102; Issue: 2 Linguagem: Inglês

10.1111/j.1432-1033.1979.tb04272.x

1432-1033

Paolo Bernardi, Giovanni Azzone, Paolo Veronese,

ATP Synthase and ATPases Research

The paper reports an investigation on ΔpH‐driven Ca 2+ fluxes in rotenone‐treated rat liver mitochondria. The H + concentration gradient (acidic inside) required to drive Ca 2+ influx is obtained from the K + concentration gradient through a H + /K + exchange. The rate of H + /K + exchange is very low in native mitochondria and is markedly enhanced by the electroneutral ionophore nigericin. The rate of Ca 2+ influx depends on the rate of generation of ΔpH; it is negligible in native mitochondria and fast after nigericin. The process of ΔpH‐driven Ca 2+ influx shows three basic features. First, the rate of Ca 2+ influx is markedly increased by the addition of uncouplers. Second, the rate of Ca 2+ influx is inhibited by ruthenium red with the same sensitivity as the processes driven by the H + pump or K + diffusion. The electroneutral H + /Ca 2+ ionophore A23187 restores Ca 2+ influx in mitochondria inhibited by ruthenium red. Third, both rate and extent of ΔpH‐driven Ca 2+ influx are inhibited by the addition of weak bases but not of weak acids. The process of ΔpH‐driven Ca 2+ influx is accompanied by H + efflux. A correlation also exists between generation of ΔpH (acidic inside) due to H + /K + exchange and utilization of ΔpH due to H + /Ca 2+ exchange. The process of ΔpH‐driven, A23187‐catalyzed, H + /Ca 2+ exchange is not preceeded by rapid H + /K + exchange in the absence of nigericin. After termination of the phase of Ca 2+ influx a phase of Ca 2+ efflux ensues. Ca 2+ efflux is not coupled to H + or K + reentry and is completely inhibited by ruthenium red. Ca 2+ efflux is not observed when Ca 2+ transport is catalyzed by A23187 in mitochondria inhibited by ruthenium red. Furthermore A23187 abolishes Ca 2+ efflux also when Ca 2+ influx occurs in the absence of ruthenium red. The data suggest that the ΔpH‐driven Ca 2+ influx and the subsequent Ca 2+ efflux take place through the native carrier as electrical uniport.