title: Voltage-clamp studies of gap junctions between uterine muscle cells during term and preterm labor.
abstract: Gap junctions between myometrial cells increase dramatically during the final stages of pregnancy. To study the functional consequences, we have applied the double-whole-cell voltage-clamp technique to freshly isolated pairs of cells from rat circular and longitudinal myometrium. Junctional conductance was greater between circular muscle-cell pairs from rats delivering either at term (32 +/- 16 nS, mean +/- SD, n = 128) or preterm (26 +/- 17 nS, n = 33) compared with normal preterm (4.7 +/- 7.6 nS, n = 114) and postpartum (6.5 +/- 10 nS, n = 16); cell pairs from the longitudinal layer showed similar differences. The macroscopic gap junction currents decayed slowly from an instantaneous, constant-conductance level to a steady-state level described by quasisymmetrical Boltzmann functions of transjunctional voltage. In half of circular-layer cell pairs, the voltage dependence of myometrial gap junction conductance is more apparent at smaller transjunctional voltages (< 30 mV) than for other tissues expressing mainly connexin-43. This unusual degree of voltage dependence, although slow, operates over time intervals that are physiologically relevant for uterine muscle. Using weakly coupled pairs, we observed two unitary conductance states: 85 pS (85-90% of events) and 25 pS. These measurements of junctional conductance support the hypothesis that heightened electrical coupling between the smooth muscle cells of the uterine wall emerges late in pregnancy, in preparation for the massive, coordinate contractions of labor.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston 77555-1062, USA.
authors.forename: H
authors.initials: H
authors.lastname: Miyoshi
authors.forename: M B
authors.initials: MB
authors.lastname: Boyle
authors.forename: L B
authors.initials: LB
authors.lastname: MacKay
authors.forename: R E
authors.initials: RE
authors.lastname: Garfield
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000777:Anesthetics / Q000494:pharmacology; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D018031:Connexin 43 / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D005260:Female; D005455:Fluorescent Antibody Technique; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D006221:Halothane / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007743:Labor, Obstetric / Q000502:physiology*; D009215:Myometrium / Q000187:drug effects / Q000502:physiology*; D007752:Obstetric Labor, Premature / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D051381:Rats; D013997:Time Factors; D014590:Uterine Contraction / Q000502:physiology
chemical_list: D000318:Adrenergic beta-Agonists; D000777:Anesthetics; D018031:Connexin 43; D000242:Cyclic AMP; D007545:Isoproterenol; D006221:Halothane