Combined modulation of the mitochondrial ATP-dependent potassium channel and the permeability transition pore causes prolongation of the biphasic calcium dynamics.

The permeability transition pore (PTP) and the ATP-dependent potassium (mtK-ATP) channel of mitochondria are known to play key roles in mitochondrially mediated apoptosis. We investigated how modulation of the permeability transition pore (PTP) and the ATP-dependent potassium (mtK-ATP) channel, either as single elements or in combination, affects the proapoptotic intracellular calcium (Ca(2+)) transients and the mitochondrial membrane potential (psi(m)). For this purpose a model was established exploring the Ca(2+) transients in N2A cells using continuous application of ATP that causes a biphasic Ca(2+) response. This response was sensitive to endoplasmatic reticulum (ER) Ca(2+) depletion and a smooth ER Ca(2+)-ATPase (SERCA) antagonist. PTP inhibition by cyclosporine A (CsA) or its non-immunosuppressive derivative NIM811 caused an amplification of the secondary Ca(2+) peak and induced a hyperpolarization of psi(m). Both the putative mtK-ATP channel inhibitor 5-hydroxydecanoate (5-HD) and the opener diazoxide ameliorated the ATP-induced secondary Ca(2+) peak. The effect of diazoxide was accompanied by a depolarization of psi(m) whereas 5-HD had no effect on psi(m). When diazoxide and CsA or NIM811 were applied together the secondary Ca(2+) rise did not return to baseline and a not significant hyperpolarization of psi(m) was observed. So, simultaneous inhibition of PTP and activation of the mtK-ATP channel prevents the increased slope of the secondary Ca(2+) peak induced by CsA (or NIM811) and also the depolarization after diazoxide application. Hence, we propose that modulation of one of these channels leads to functional changes of the other channel by means of DeltaCa(2+) and Deltapsi(m).