Lack of connexin 40 decreases the calcium sensitivity of renin-secreting juxtaglomerular cells

Alteration of Cx37, Cx40, Cx43, Cx45, Panx1, and Renin Expression Patterns in Postnatal Kidneys of Dab1-/- (yotari) Mice

Numerous evidence corroborates roles of gap junctions/hemichannels in proper kidney development. We analyzed how Dab1 gene functional silencing influences expression and localization of Cx37, Cx40, Cx43, Cx45, Panx1 and renin in postnatal kidneys of yotari mice, by using immunohistochemistry and electron microscopy. Dab1 Δ102/221 might lead to the activation of c-Src tyrosine kinase, causing the upregulation of Cx43 in the medulla of yotari mice. The expression of renin was more prominent in yotari mice (p < 0.001). Renin granules were unusually present inside the vascular walls of glomeruli capillaries, in proximal and distal convoluted tubules and in the medulla. Disfunction of Cx40 is likely responsible for increased atypically positioned renin cells which release renin in an uncontrolled fashion, but this doesn't rule out simultaneous involvement of other Cxs, such as Cx45 which was significantly increased in the yotari cortex. The decreased Cx37 expression in yotari medulla might contribute to hypertension reduction provoked by high renin expression. These findings imply the relevance of Cxs/Panx1 as markers of impaired kidney function (high renin) in yotari mice and that they have a role in the preservation of intercellular signaling and implicate connexopathies as the cause of premature death of yotari mice.

Myoendothelial communication in the renal vasculature and the impact of drugs used clinically to treat hypertension

The renal vasculature has many peculiarities including highly irregular branching. Renal blood flow must sustain adequate perfusion and maintain a high glomerular filtration. Renal autoregulation helps control renal blood flow. The local autoregulatory mechanism, tubuloglomerular feedback, elicits a vasoconstriction that can be found not only in neighboring nephrons but over large areas of the kidney indicating that the renal vasculature supports strong conduction of vascular responses. The basis for conduction is intercellular communication through gap junctions. The endothelium is strongly coupled and serves as a vascular conduction highway leading the signal to the vascular smooth muscle cells through myoendothelial coupling. Extensive intercellular coupling is also found in renin secreting cells where gap junctions seem to tie the cells together to improve control of renin secretion. Lack of coupling leads to dysregulation of renin secretion and hypertension. However, the activity of the renin-angiotensin system also controls gap junction expression in the kidney. Treatment reducing angiotensin II activity, as used in hypertension treatment, can affect expression of renal and vascular gap junction.

Ablation of both Cx40 and Panx1 results in similar cardiovascular phenotypes exhibited in Cx40 knockout mice

Connexins (Cxs) and pannexins (Panxs) are highly regulated large-pore channel-forming proteins that participate in cellular communication via small molecular exchange with the extracellular microenvironment, or in the case of connexins, directly between cells. Given the putative functional overlap between single membrane-spanning connexin hemichannels and Panx channels, and cardiovascular system prevalence, we generated the first Cx40-/-Panx1-/- mouse with the anticipation that this genetic modification would lead to a severe cardiovascular phenotype. Mice null for both Cx40 and Panx1 produced litter sizes and adult growth progression similar to wild-type (WT), Cx40-/- and Panx1-/- mice. Akin to Cx40-/- mice, Cx40-/-Panx1-/- mice exhibited cardiac hypertrophy and elevated systolic, diastolic, and mean arterial blood pressure compared with WT and Panx1-/- mice; however assessment of left ventricular ejection fraction and fractional shortening revealed no evidence of cardiac dysfunction between groups. Furthermore, Cx40-/-, Panx1-/-, and Cx40-/-Panx1-/- mice demonstrated impaired endothelial-mediated vasodilation of aortic segments to increasing concentrations of methacholine (MCh) compared with WT, highlighting roles for both Cx40 and Panx1 in vascular endothelial cell (EC) function. Surprisingly, elevated kidney renin mRNA expression, plasma renin activity, and extraglomerular renin-producing cell populations found in Cx40-/- mice was further exaggerated in double knockout mice. Thus, while gestation and gross development were conserved in Cx40-/-Panx1-/- mice, they exhibit cardiac hypertrophy, hypertension, and impaired endothelial-mediated vasodilation that phenocopies Cx40-/- mice. Nevertheless, the augmented renin homeostasis observed in the double knockout mice suggests that both Cx40 and Panx1 may play an integrative role.