The role of ADP in the modulation of the calcium-efflux pathway in rat brain mitochondria

Abstract

The role of ADP in the regulation of Ca2+ efflux in rat brain mitochondria was investigated. ADP was shown to inhibit Ruthenium-Red-insensitive H+-and Na+-dependent Ca2+-efflux rates if Pi was present, but had no effect in the absence of Pi. The primary effect of ADP is an inhibition of Pi efflux, and therefore it allows the formation of a matrix Ca2+-P, complex at concentrations above 0.2mM-Pt and 25nmol of Ca2+/mg of protein, which maintains a constant free matrix Ca2+ concentration. ADP inhibition of Pi and Ca2+ efflux (a) is nucleotide-specific, since in the presence of oligomycin and an inhibitor of adenylate kinase ATP does not substitute for ADP, (b) is dependent on the amount of ADP present, and (c) requires ADP concentrations in excess of the concentrations of translocase binding sites. Brain mitochondria incubated with 0.2mM-Pi and ADP (a) showed Ca2+-efflux rates dependent on Ca2+ loads at Ca2+ concentrations below those required for the formation of a Pi-Ca2+ complex, and (b) behaved as perfect cytosolic buffers exclusively at high Ca2+ loads. The possible role of brain mitochondrial Ca2+ in the regulation of the tricarboxylic acid-cycle enzymes and in buffering cytosolic Ca2+ is discussed.

Calcium Signaling in Brain Mitochondria

“…After the addition of Ca 2ϩ (40 nmol/mg protein, giving 5 M free Ca 2ϩ ), most of it was taken up by energized mitochondria. However, the total amount of Ca 2ϩ taken up after glutamate addition was higher in the absence than in the presence of Na ϩ (about 41 Ϯ 1.6 versus 26.6 Ϯ 3.7 nmol/mg protein in MSK and MSKNa, respectively), as observed previously with rat brain mitochondria (58,67). Interestingly, MAS activity measured in these two conditions varied inversely with the accumulated Ca 2ϩ .…”

Effects of cyclosporine A and its immunosuppressive or non-immunosuppressive derivatives [D-Ser]8-CsA and Cs9 on mitochondria from different brain regions

“…This effect was probably due to a stabilization of the PTP by ADP on the outer side of mitochondrial inner membrane. This effect has been demonstrated already in liver (Gizatullina et al, 2005) and brain mitochondria (Vitorica and Satrústegui, 1985;Brustovetsky et al, 2003). In conclusion, we assume that under physiological conditions BM, as mitochondria from other tissues, are sensitive to CsA.…”

“…4A, B, O). Also other authors have found that CsA effects on BM require low ADP concentrations (Vitorica and Satrústegui, 1985;Brustovetsky et al, 2003;Hansson et al, 2004). However, they used low ADP levels in combination with oligomycin in order to inhibit ADP phosphorylation to ATP.…”

“…This decision was based on our observation that ADP and ATP have similar abilities to support mitochondrial CsA effects (Gizatullina and Gellerich, unpublished data). Moreover, oligomycin cannot prevent the equilibration of ADP, AMP and ATP catalyzed by the adenylate kinase, a mitochondrial enzyme localized in the intermembrane space (Vitorica and Satrústegui, 1985;Wustmann et al, 1987). If ADP was used in a higher concentration (100 μM), a further and pronounced increase of Ca 2+ thresholds required for PT was observed (not shown).…”

“…However, they used low ADP levels in combination with oligomycin in order to inhibit ADP phosphorylation to ATP. This experimental design was based on the assumption that ATP itself does not affect CsA effects (Vitorica and Satrústegui, 1985). In contrast, we avoided the use of oligomycin.…”