α7 nicotinic acetylcholine receptors control cytochrome c release from isolated mitochondria through kinase-mediated pathways

Nicotinic acetylcholine receptors are ligand-gated ion channels found in the plasma membrane of both excitable and non-excitable cells. Previously we reported that nicotinic receptors containing alpha 7 subunits were present in the outer membranes of mitochondria to regulate the early apoptotic events like cytochrome c release. Here we show that signaling of mitochondrial alpha 7 nicotinic receptors affects intramitochondrial protein kinases. Agonist of alpha 7 nicotinic receptors PNU 282987 (30 nM) prevented the effect of phosphatidyl inositol-3-kinase inhibitor wortmannin, which stimulated cytochrome c release in isolated mouse liver mitochondria, and restored the Akt (Ser 473) phosphorylation state decreased by either 90 mu M Ca2+ or wortmannin. The effect of PNU 282987 was similar to inhibition of calcium-calmodulin-dependent kinase II (upon 90 mu M Ca2+) or of Src kinase(s) (upon 0.5 mM H2O2) and of protein kinase C. Cytochrome c release from mitochondria could be also attenuated by alpha 7 nicotinic receptor antagonist methyllicaconitine or alpha 7-specific antibodies. Allosteric modulator PNU 120526 (1 mu M) did not improve the effect of agonist PNU 282987. Acetylcholine (1 mu M) and methyllicaconitine (10 nM) inhibited superoxide release from mitochondria measured according to alkalization of Ca2+-containing inedium. It is concluded that alpha 7 nicotinic receptors regulate mitochondrial permeability transition pore formation through ion-independent mechanism involving activation of intramitochondrial PI3K/Akt pathway and inhibition of calcium-calmodulin-dependent or Src-kinase-dependent signaling pathways. (C) 2014 Elsevier Ltd. All rights reserved.