DIFFERENTIAL EXPRESSION AND REGULATION OF CONNEXIN-43 AND CELL-CELL COUPLING IN MYOCYTES FROM THE CIRCULAR AND LONGITUDINAL LAYERS OF BOVINE MYOMETRIUM

The expression and localization of the gap junction protein connexin-43 (Cx-43) as well as functional coupling were studied in myocytes from the two layers of the bovine myometrium: the circular and the longitudinal layers. Intercellular communication (measured by Lucifer yellow dye transfer through gap junctions) was more intense in the circular than in the longitudinal layer of the bovine myometrium. The circular layer also exhibited a greater degree of punctuate immunofluorescence to Cx-43. Myocytes from the circular layer expressed more Cx-43 messenger RNA(mRNA; 2.38 +/- 0.46, Cx-43 over 18S RNA) than the longitudinal layer (1.46 +/- 0.48, Cx-43 over 18S RNA; P < 0.05). The modulation of Cx-43 expression by sex steroids in the two myometrial layers was tested using a pure steroidal antiestrogen, EM-139. In myocytes from the circular layer, the level of Cx-43 mRNA was decreased after treatment with 0.1 mu M. EM-139 (1.37 +/- 0.25, Cx-43 over 18S RNA) compared to that in untreated cells (2.38 +/- 0.46, Cx-43 over 18S RNA), representing a 40% inhibition. In parallel, cell-cell coupling and the amount of Cx-43 protein were also reduced after antiestrogen treatment. In contrast, treatment of cells from the longitudinal layer with the antiestrogen did not significantly affect the level of Cx-43 mRNA, protein, or cell-cell coupling. These data demonstrate that Cx-43 protein and mRNA are expressed and regulated differentially in myocytes from the circular and longitudinal layers of bovine myometrium. Furthermore, the circular myometrial layer may represent a preferential target for estrogen regulation of the biochemical and mechanical processes controlling contractility.