Results 1K1C Procedure Induces Volume-Dependent

After a chronic increase in blood pressure, arteries undergo alterations of endothelial (ECs) and smooth muscle cells (SMCs) because of hemodynamic changes.1 Specifically, hypertension results in the hypertrophic remodeling of arterial walls,2,3 which associates with altered expression of connex-ins (Cxs).4–8 These proteins form channels for the commu-nication of ECs and SMCs, which is needed to coordinate vasoconstriction and vasodilation along the vessels.9 ECs pre-dominantly express Cx37 and Cx40,5–7 whereas SMCs mostly express Cx43 and Cx45.5,6,10 Mice lacking Cx40 feature hyper-tension4,6,11,12 because of increased secretion of renin4,13 and reduced relaxation of peripheral vessels.14 This effect may be the link to the decreased expression of endothelial nitric oxide synthase (eNOS),5,15 which impairs the release of NO, whereby ECs usually relax SMCs.4–6,13 Thus, restoration of Cx40 in ECs of Cx40−/ − mice normalizes eNOS levels,8 sug-gesting an interaction between these proteins. As yet, how-ever, such interaction has not been tested during hypertension. To investigate this question, we have subjected wild-type (WT) and Cx40-null mice (Cx40−/−)4,13 to conditions induc-ing hypertension by either volume overload (after a 1-kidney, 1-clip [1K1C] procedure16,17) or renin overproduction (after a 2-kidney, 1-clip [2K1C] procedure6). We show that Cx40 consistently increased in aortic ECs, whereas Cx37 and Cx45 increased in SMCs, irrespective of the mechanism leading to hypertension. In contrast, Cx43 only increased in SMCs during renin-dependent hypertension. The volume-dependent hypertension of WT mice was associated with an increased interaction between Cx40 and Cx37 with eNOS, whereas Cx40−/ − null mice featured decreased levels of eNOS and increased phosphorylation of the enzyme. The results provide evidence that Cx40 and Cx37 of ECs activate different signal-ing mechanisms depending on the cause of hypertension