Role of Mitochondria in the Generation of Acetylcholine-Induced Calcium Transients in Rat Chromaffin Cells

A fluorescent probe, FURA-2M, was used to examine the role of mitochondria in the generation of calcium transients evoked by acetylcholine (ACh) in isolated rat chromaffin cells. Our experiments showed that application of 10 M CCCP (carbonyl cyanide m-chlorophenylhydrazone, a mitochondrial protonophore) caused significant intracellular calcium transients (F1/F2 wave ratio 1.05). Application of CCCP did not affect the successive responses to repeated ACh applications in a cell subpopulation with the domination of nicotinic receptors (F1/F2 = 0.90 in control, and F1/F2 = 0.89 after CCCP application). In cells with the domination of muscarinic receptors, responses to repeated ACh applications decreased under control conditions. Application of CCCP caused recovery of the successive ACh responses by 27%, as compared with the control. The results allow us to suggest that the mitochondria themselves are not directly involved in the ACh-induced calcium transients, but calcium release from the mitochondria during CCCP treatment can cause the replenishment of other intracellular stores (endoplasmic reticulum) and in such a way recover the ACh responses to repeated stimulations in the cells with dominating metabotropic receptors.