To investigate the role of chronic mitochondrial dysfunction on intracellul
ar calcium signaling, we studied basal and stimulated cytosolic calcium lev
els in SH-SY5Y cells and a derived cell line devoid of mitochondrial DNA (R
ho degrees). Basal cytosolic calcium levels were slightly but significantly
reduced in Rho degrees cells, The impact of chronic depletion of mitochond
rial DNA was more evident following exposure of cells to carbachol, a calci
um mobilizing agent. Calcium transients generated in Rho degrees cells foll
owing 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 degrees cells. The rapid calcium transie
nts in Rho degrees cells were due, in part, to increased reliance on Na+/Ca
2+ exchange activity at the plasma membrane and the plateau phase in calciu
m recovery in SH-SY5Y cells was dependent on the presence of extracellular
calcium. We also examined whether mitochondrial DNA depletion influenced ca
lcium responses to release of intracellular calcium stores. Rho degrees cel
ls showed reduced responses to the uncoupler, FCCP, and the sarcoplasmic re
ticulum calcium ATPase inhibitor, thapsigargin. Acute exposure of SH-SY5Y c
ells to mitochondrial inhibitors did not mimic the results seen in Rho degr
ees 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. (C) 2000 Elsevier Science B.V. All rights
reserved.