Expression of homocellular and heterocellular gap junctions in hamster arterioles and feed arteries.

Conduction of vasoconstrictor and vasodilator responses in the microcirculation involves electrical coupling through gap junction channels among cells of the vascular wall. The present study determined whether reported differences in the properties of conduction along the arterioles of the epithelial hamster cheek pouch (CPA) and feed arteries of its retractor skeletal muscle (RFA) result from differences in the expression profile of specific connexin (Cx) isoforms and the gap junctions they comprise. Real-time PCR, immunohistochemistry and serial section electron microscopy were used to compare wall morphology and the distribution of gap junctions between respective vessels. Expression of mRNA for Cx37, 40, 43 and 45 was similar between CPA and RFA. In the endothelium, Cx37, 40 and 43 proteins were expressed abundantly between adjacent cells while Cx37 was present in the smooth muscle. In both vessels, endothelial and smooth muscle cell (SMC) layers were well connected by myoendothelial gap junctions (MEGJs), which were found near endothelial cell (EC) gap junctions. The absence of differential gap junctional expression between CPA and RFA, in spite of documented differences in cellular conduction pathways, supports the hypothesis that conductance of vascular gap junction channels can be differentially modulated in resistance microvessels.