Mitochondrial DNA-depleted neuroblastoma (Rho°) cells exhibit altered calcium signaling

Abstract

To investigate the role of chronic mitochondrial dysfunction on intracellular calcium signaling, we studied basal and stimulated cytosolic calcium levels in SH-SY5Y cells and a derived cell line devoid of mitochondrial DNA (Rho°). Basal cytosolic calcium levels were slightly but significantly reduced in Rho° cells. The impact of chronic depletion of mitochondrial DNA was more evident following exposure of cells to carbachol, a calcium mobilizing agent. Calcium transients generated in Rho° cells following application of carbachol were more rapid than those in SH-SY5Y cells. A plateau phase of calcium recovery during calcium transients was present in SH-SY5Y cells but absent in Rho° cells. The rapid calcium transients in Rho° cells were due, in part, to increased reliance on Na +/Ca 2+ exchange activity at the plasma membrane and the plateau phase in calcium recovery in SH-SY5Y cells was dependent on the presence of extracellular calcium. We also examined whether mitochondrial DNA depletion influenced calcium responses to release of intracellular calcium stores. Rho° cells showed reduced responses to the uncoupler, FCCP, and the sarcoplasmic reticulum calcium ATPase inhibitor, thapsigargin. Acute exposure of SH-SY5Y cells to mitochondrial inhibitors did not mimic the results seen in Rho° cells. These results suggest that cytosolic calcium homeostasis in this neuron-like cell line is significantly altered as a consequence of chronic depletion of mitochondrial DNA.