Effect of gap junction number and permeability on intercellular coupling in rat myometrium

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Abstract
Gap junctions (GJ) increase between myometrial cells immediately before labor. To provide evidence of their role in cell-to-cell coupling, we evaluated input resistance (Ro) and intercellular spread of Lucifer yellow (LY) in intact preparations of rat longitudinal myometrium of preterm, term, and antiprogesterone-treated preterm delivering animals. LY injected into cells from either term or preterm delivering rats (many GJ) spread rapidly to neighboring cells by 60 s, but in preparations from nondelivering controls required 4-6 min to become detectable in adjacent cells. Ro of cells in preterm nondelivering preparations was 24.1 +/- 0.8 (SE) M omega, but dropped to 12.0 +/- 0.4 M omega (P less than 0.05) at delivery, similar to preterm delivering tissues at 13.8 +/- 0.6 M omega. The putative GJ uncoupling agent octanol reversibly increased Ro of term- and preterm-delivering tissues fourfold (P less than 0.01) within 60 s, and Ro of preterm-nondelivering tissue was further increased so that Ro values were similar among the three classes. These increased Ro values are interpreted as decreased coupling. Both K+ depolarization and oxytocin (10(-8) to 10(-6) M) increased Ro of delivering tissues (P less than 0.05), suggesting that high levels of contractile agonists may lead to reduced cell-to-cell coupling. Therefore, myometrial coupling can be modulated over seconds via GJ permeability as well as over hours by GJ number.