Regional differentiation of desmin, connexin43, and connexin45 expression patterns in rat aortic smooth muscle

The gap-junctional protein, connexin43, is differentially expressed in vasc ular smooth muscle cells (SMCs) according to phenotype. Previous studies su ggest that desmin-negative SMCs are characterized by high levels of connexi n43, whereas desmin-positive SMCs (of a more contractile phenotype) typical ly have low connexin43 levels. In this study, we examine systematically the inverse relationship between connexin43 and desmin in SMCs of defined regi ons of the rat aortic media and determine whether additional connexin isoty pes are expressed and contribute to this relationship. Immunoconfocal micro scopy demonstrated that (1) the inverse relationship between connexin43 and desmin expression holds true for the media of sequential aortic zones, wit h 1 exception, the ascending aorta, and (2) an additional vascular connexin , connexin45, is expressed by aortic SMCs. Examination of connexin43, conne xin45, and desmin expression in sequential aortic zones reveals 3 SMC subpo pulations. The first, predominating in the aortic arch and thoracic aorta, is desmin negative and contains high connexin43 levels; the second, predomi nating in the abdominal aorta and iliac artery, is desmin positive and cont ains low connexin43 levels; and the third, which is restricted to the ascen ding aorta, is desmin positive and expresses high connexin43 levels. Connex in45 levels are high in the ascending aorta but low in the other aortic seg ments. In para-aortic veins, a fourth SMC subpopulation appears, one that i s desmin positive and contains connexin45 but not connexin43. These results demonstrate that a diversity of connexin expression patterns characterizes distinctive subpopulations of medial SMCs in situ with a potential to cont ribute to regional differentiation of vascular function.