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

摘要

class="enumerated" style="list-style-type:decimal">The Ca²⁺-sensitive fluorescent indicator rhod-2 was used to measure mitochondrial [Ca²⁺] ([Ca²⁺]m) in single smooth muscle cells from the rat pulmonary artery, while simultaneously monitoring cytosolic [Ca²⁺] ([Ca²⁺]i) with fura-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.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.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.This study provides direct evidence that Ca²⁺ release from the sarcoplasmic reticulum, either through ryanodine or inositol 1,4,5-trisphosphate (InsP3) 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.