Release of Ca2+ from the sarcoplasmic reticulum increases mitochondrial [Ca2+] in rat pulmonary artery smooth muscle cells

1. The Ca2+-sensitive fluorescent indicator rhod-2 was used to measure mitochondrial [Ca2+] ([Ca2+](i)) in single smooth muscle cells from the rat pulmonary artery while simultaneously monitoring cytosolic [Ca2+] ([Ca2+](i)) with fura-2. 2. Application of caffeine produced an increase in [Ca2+](i) and also increased [Ca2+](m). The increase in [Ca2+](m) occurred after the increase in [Ca2+](i), and remained elevated for a considerable time after [Ca2+](i) had returned to resting values. 3. The protonophore carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP), which causes the mitochondrial membrane potential to collapse, markedly attenuated the increase in [Ca2+](m) following caffeine application and also increased the half-time for recovery of [Ca2+](i) to resting values. 4. Activation of purinoceptors with ATP also produced increases in both [Ca2+](i) and [Ca2+](m) in these smooth muscle cells. In some cells, oscillations in [Ca2+](i) were observed during ATP application, which produced corresponding oscillations in [Ca2+](m) and membrane currents. 5. This study provides direct evidence that Ca2+ release from the sarcoplasmic reticulum, either through ryanodine or inositol 1,4,5-trisphosphate (InsP(3)) receptors, increases both cytosolic and mitochondrial [Ca2+] in smooth muscle cells. These results have potential implications both for the role of mitochondria in Ca2+ regulation in smooth muscle, and for understanding how cellular metabolism is regulated.