title: Oxytocin induces an inward current in pregnant rat myometrial cells.
abstract: The effects of oxytocin (OT) on holding current were studied in uterine smooth muscle cells freshly isolated from the longitudinal layer of 18-20 day pregnant rats, using the nystatin method of whole-cell voltage clamp. As we previously reported, the voltage-dependent Ca2+ current (L type) was partially inhibited by OT (about 30% inhibition at 1 microM). When the cells were held at the holding potential (HP) of -60 mV and the holding current was monitored, OT induced an inward current. The amplitude of this OT-induced current was 72 +/- 26 pA (n = 27). When the cell was held at more positive potentials (HP 0 or +40 mV), the OT-induced current reversed direction, becoming outward. This current usually was long lasting (74% of cells responding to OT); a transient current was observed in 26% of the cells. In the absence of either Na+ or Ca2+ in the bath solution, OT induced an inward current (at HP -60 mV). However, the OT-induced current was absent when both of these ions were omitted from the bath. These results suggest that OT induces an inward current through receptor-activated nonselective cation channels. The resulting increase of intracellular Ca2+ may contribute to the inhibition of voltage-dependent Ca2+ current produced by OT. This OT-induced current may also play an important role for membrane depolarization and accompanying contraction produced by OT in pregnant rat myometrium.
authors.affiliation: Department of Physiology and Biophysics, College of Medicine, University of Cincinnati, OH 45267.
authors.forename: K
authors.initials: K
authors.lastname: Shimamura
authors.forename: M
authors.initials: M
authors.lastname: Kusaka
authors.forename: N
authors.initials: N
authors.lastname: Sperelakis
mesh_terms: D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009215:Myometrium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009761:Nystatin; D010121:Oxytocin / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007473:Ion Channels; D009761:Nystatin; D010121:Oxytocin