In the vasculature, gap junctions (GJ) play a multifaceted role by serving as direct conduits for cell–cell intercellular communication via the facilitated diffusion of signaling molecules. GJs are essential for the control of gene expression and coordinated vascular development in addition to vascular function. The coupling of endothelial cells to each other, as well as with vascular smooth muscle cells via GJs, plays a relevant role in the control of vasomotor tone, tissue perfusion and arterial blood pressure. The regulation of cell-signaling is paramount to cardiovascular adaptations of pregnancy. Pregnancy requires highly developed cell-to-cell coupling, which is affected partly through the formation of intercellular GJs by Cx43, a gap junction protein, within adjacent cell membranes to help facilitate the increase of uterine blood flow (UBF) in order to ensure adequate perfusion for nutrient and oxygen delivery to the placenta and thus the fetus. One mode of communication that plays a critical role in regulating Cx43 is the release of endothelial-derived vasodilators such as prostacyclin (PGI2) and nitric oxide (NO) and their respective signaling mechanisms involving second messengers (cAMP and cGMP, respectively) that are likely to be important in maintaining UBF. Therefore, the assertion we present in this review is that GJs play an integral if not a central role in maintaining UBF by controlling rises in vasodilators (PGI2 and NO) via cyclic nucleotides. In this review, we discuss: (1) GJ structure and regulation; (2) second messenger regulation of GJ phosphorylation and formation; (3) pregnancy-induced changes in cell-signaling; and (4) the role of uterine arterial endothelial GJs during gestation. These topics integrate the current knowledge of this scientific field with interpretations and hypotheses regarding the vascular effects that are mediated by GJs and their relationship with vasodilatory vascular adaptations required for modulating the dramatic physiological rises in uteroplacental perfusion and blood flow observed during normal pregnancy.

Uterine vascular adaptations facilitate rises in uterine blood flow (UBF) during pregnancy, which are associated with gap junction connexin (Cx) proteins and eNOS. In uterine artery endothelial cells (UAECs) ATP activates eNOS in a pregnancy (P) specific manner that is dependent on Cx43 function. Caveolar subcellular domain partitioning plays key roles in ATP-induced eNOS activation and NO production. Little is known regarding the partitioning of Cx proteins to caveolar domains or their dynamics upon ATP treatment. We observed that Cx43-mediated gap junction function upon ATP stimulation is associated with Cx43 re-partitioning between the non-caveolar and caveolar domains. Compared to UAECs from nonpregnant (NP) ewes, levels of ATP, PGI2, cAMP, NOx, and cGMP were 2-fold higher (P<0.05) in P-UAECs. In P-UAECs ATP increased lucifer yellow dye transfer, a response abrogated by Gap27, but not Gap 26 indicating involvement of Cx43 but not Cx37. Confocal microscopy revealed domain partitioning of Cx43 and Cav-1. In P-UAECs LC/MS/MS analysis revealed only Cx43 in the caveolar domain. In contrast, Cx37 was located only in the non-caveolar pool. Western analysis revealed that ATP increased Cx43 distribution (1.7-fold;P=0.013) to the caveolar domain, but had no effect on Cx37. These data demonstrate rapid ATP-stimulated repartitioning of Cx43 to the caveolae, where eNOS resides and plays an important role in NO-mediated increasing UBF during pregnancy.

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