ΔpH Induced Calcium Fluxes in Rat Liver Mitochondria

Abstract

The paper reports an investigation on ΔpH‐driven Ca2+ fluxes in rotenone‐treated rat liver mitochondria. The H+ concentration gradient (acidic inside) required to drive Ca2+ 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 Ca2+ influx depends on the rate of generation of ΔpH; it is negligible in native mitochondria and fast after nigericin. The process of ΔpH‐driven Ca2+ influx shows three basic features. First, the rate of Ca2+ influx is markedly increased by the addition of uncouplers. Second, the rate of Ca2+ influx is inhibited by ruthenium red with the same sensitivity as the processes driven by the H+ pump or K+ diffusion. The electroneutral H+/Ca2+ ionophore A23187 restores Ca2+ influx in mitochondria inhibited by ruthenium red. Third, both rate and extent of ΔpH‐driven Ca2+ influx are inhibited by the addition of weak bases but not of weak acids. The process of ΔpH‐driven Ca2+ 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+/Ca2+ exchange. The process of ΔpH‐driven, A23187‐catalyzed, H+/Ca2+ exchange is not preceeded by rapid H+/K+ exchange in the absence of nigericin. After termination of the phase of Ca2+ influx a phase of Ca2+ efflux ensues. Ca2+ efflux is not coupled to H+ or K+ reentry and is completely inhibited by ruthenium red. Ca2+ efflux is not observed when Ca2+ transport is catalyzed by A23187 in mitochondria inhibited by ruthenium red. Furthermore A23187 abolishes Ca2+ efflux also when Ca2+ influx occurs in the absence of ruthenium red. The data suggest that the ΔpH‐driven Ca2+ influx and the subsequent Ca2+ efflux take place through the native carrier as electrical uniport.

An electrogenic uniport mediates light‐dependent Ca2+ influx into intact spinach chloroplasts

“…On a protein basis the chloroplastic Ca'+ influx rates are similar to those of plant [31] and rat liver mitochondria [27]. From a comparison of k,,, values it has been concluded that the affinity of the mitochondrial system is at least lo-fold lower than the affinity of the plasma membrane system [23].…”

“…Comparison with mitochondrial Cd" influx systems Ca*+ influx into animal [25,27] and plant mitochondria [23,24] is mediated by an electrogenic uniport-carrier system similar to that described here for chloroplasts. The influx is sensitive to ruthenium red [24-271 and has been shown to be under the control of AE [28,29].…”

“…Two criteria have been used to distinguish between Ca2+ influx mediated by a uniport-type carrier and that mediated by a Ca2+/H+-exchange carrier [27]: uniport-type influx is sensitive to ruthenium red and enhanced by uncouplers. These criteria for a uniport-type carrier are met by the light-dependent Ca2' influx into spinach chloroplasts.…”

The Mitochondrial Permeability Transition Pore is Modulated by Oxidative Agents Through Both Pyridine Nucleotides and Glutathione at Two Separate Sites

“…Pore opening was rnonitored as the apparent absorbance change at 540 nm following membrane permeabilization to solutes. Although similar in principle to the incubation conditions of a previous study [I51 and to those employed by others [21,221, the use of potassium gluconate rather than sucrose ensured that the Donnan potential was collapsed and thus that an inside-acidic ApH did not form, which could in principle sustain a Ca2+ concentration gradient in the presence of FCCP and A23187 [23].…”

Acidosis Promotes the Permeability Transition in Energized Mitochondria: Implications for Reperfusion Injury

“…Although a pH gradient can indeed drive Ca 21 accumulation, which is more readily observed in deenergized mitochondria (Bernardi and Azzone, 1979), in energized mitochondria the driving force for Ca 21 accumulation is the electrical potential difference rather than the delta pH.…”