Extracellular calcium depletion transiently elevates oxygen consumption in neurosecretory PC12 cells through activation of mitochondrial Na+/Ca2+ exchange

Fluctuating extracellular Ca2+ regulates many aspects of neuronal (patho)physiology including cell metabolism and respiration. Using fluorescence-based intracellular oxygen sensing technique, we demonstrate that depletion of extracellular Ca2+ from 1.8 to 0.6 mM by chelation with EGTA induces a marked spike in O-2 consumption in differentiated PC12 cells. This respiratory response is associated with the reduction in cytosolic and mitochondrial Ca2+, minor depolarization on the mitochondrial membrane, moderate depolarization of plasma membrane, and no changes in NAD(P)H and ATP. The response is linked to the influx of extracellular Na and the subsequent activation of mitochondrial Na+/Ca2+ and Na /H+ exchange. The mitochondrial Na /Ca2+ exchanger (mNCX) activated by Na+ influx reduces Ca-2 and increases Na levels in the mitochondrial matrix. The excess of Na+ activates the mitochondrial Na+/H+ exchanger (NHE) increasing the outward pumping of protons, electron transport and O-2 consumption. Reduction in extracellular Na and inhibition of Na+ influx through the receptor operated calcium channels and plasmalemmal NHE reduce the respiratory response. Inhibition of the mNCX, L-type voltage gated Ca2+ channels or the release of Ca2+ from the endoplasmic reticulum also reduces the respiratory spike, indicating that unimpaired intercompartmental Ca2+ exchange is critical for response development. (C) 2010 Elsevier B.V. All rights reserved.