Connexin make-up of endothelial gap junctions in the rat pulmonary artery as revealed by immunoconfocal microscopy and triple-label immunogold electron microscopy

Integration of vascular endothelial function relies on multiple signaling m echanisms, including direct cell-cell communication through gap junctions. Gap junction proteins expressed in the endothelium include connexin37, conn exin40, and connexin43. To investigate whether individual endothelial cells in vivo express all three connexin types and, if so, whether multiple conn exins are assembled into the same gap junction plaque, we used affinity-pur ified connexin-specific antibodies raised in three different species to per mit multiple-label immunoconfocal and immunoelectron microscopy in the rat main pulmonary artery. Immunoconfocal microscopy showed a high incidence of co-localization between connexin43 and connexin40, but lower incidences of co-localization between connexin37 and connexin40 or connexin43. Immunoele ctron microscopy revealed that 83% of gap junction profiles contained all t hree connexins, with the proportion of connexin40 labeling being significan tly higher than that of connexin37 or connexin43. The presence of three dif ferent connexin types of distinct properties in vitro provides potential fo r complex regulation and functional differentiation of endothelial intercel lular communication properties in vivo.