CHLORIDE AND MONOVALENT ION-SELECTIVE CATION CURRENTS ACTIVATED BY OXYTOCIN IN PREGNANT RAT MYOMETRIAL CELLS

OBJECTIVE: The purpose of our study was to characterize the membrane mechanisms responsible for oxytocin-induced depolarization in single cells from pregnant rat myometrium. STUDY DESIGN: Membrane currents were recorded with the whole-cell mode of the standard patch-clamp technique. Intracellular calcium concentration was monitored with the fluorescence from Fura 2 added to the pipette solution. RESULTS: We found that oxytocin predominantly activates potassium, chloride, and cation conductances. Chloride and cation currents were evoked by an increase in the intracellular calcium concentration dependent on calcium release from the heparin-sensitive intracellular stores. Chloride and cation current showed different calcium dependences so that they could be activated separately. CONCLUSION: Stimulation of oxytocin receptors induces opening of calcium-activated chloride and cation channels, leading to depolarization of the myometrial cells. This depolarization opens, in turn, voltage-dependent calcium channels.