Coronaridine congeners modulate mitochondrial α3β4*nicotinic acetylcholine receptors with different potency and through distinct intra-mitochondrial pathways

In contrast to plasma membrane-expressed nicotinic acetylcholine receptors (nAChRs), mitochondrial nAChRs function in an ion-independent manner by triggering intra-mitochondrial kinases that regulate the release of cytochrome c (Cyt c), an important step in cellular apoptosis. The aim of this study is to determine the structural requirements for mitochondrial alpha 3 beta 4* nAChR activation by measuring the modulatory effects of two noncompetitive antagonists of these receptors, (+)-catharanthine and (+/-)-18-methoxycoronaridine [(+/-)-18-MC], on Cyt c release from wild-type and alpha 7-/- mice mitochondria. The sandwich ELISA results indicated that alpha 3 beta 4* nAChRs are present in liver mitochondria in higher amounts compared to that in brain mitochondria and that these receptors are up-regulated in alpha 7-/- mice. Correspondingly, (+/-)-18-MC decreased Cyt c release from liver mitochondria of wild-type mice and from brain and liver mitochondria of alpha 7-/- mice. The effect in wild-type mice mitochondria was mediated mainly by the Src-dependent pathway, regulating the apoptogenic activity of reactive oxygen species, while in alpha 7-/- mice mitochondria, (+/-)-18-MC strongly affected the calcium-calmodulin kinase II-dependent pathway. In contrast, (+)-catharanthine was much less potent than (+/-)-18-MC and triggered several signaling pathways, suggesting the involvement of multiple nAChR subtypes. These results show for the first time that noncompetitive antagonists can induce mitochondrial alpha 3 beta 4* nAChR signaling, giving a more comprehensive understanding on the function of intracellular nAChR subtypes. (C) 2017 Elsevier Ltd. All rights reserved.