Oxytocin depolarizes mitochondria in isolated myometrial cells

Oxytocin is known to play important roles in uterine contractions mediated at least in part by increasing intracellular Ca(2+) concentration ([Ca(2+)](i)), through enhancing extracellular Ca(2+) entry and Ca(2+) release from the sarcoplasmic reticulum (SR), processes that are intimately linked with mitochondria. This study examines the effects of oxytocin on mitochondrial function. This was achieved by measuring the ratiometric JC-1 fluorescence signal in isolated myometrial cells, which provides a relative measure of the mitochondrial membrane potential (Psi(m)), and also by loading the cells with BAPTA-AM Oregon Green to examine changes in [Ca(2+)](i). Oxytocin (1 nM) depolarized the Psi(m), to 73.8 +/- 3.7 of control (P0.05). The reduction in Psi(m) is likely to occur at least in part through the oxytocin-induced increase in [Ca(2+)](i) causing enhanced mitochondrial uptake of Ca(2+) and resultant dissipation of the mitochondrial electrochemical gradient. ATP synthase is also stimulated, which would further contribute to a decrease in Psi(m).