Pannexin Protein Expression in the Rat Middle Cerebral Artery

Abstract

Background: Connexin proteins are well known to participate in cell-to-cell communication within the cerebral vasculature. Pannexins are a recently discovered family of proteins that could potentially be involved in cell-to-cell communication. Herein, we sought to determine whether pannexins are expressed in rat middle cerebral artery (MCA). Methods: A combination of RT-PCR, immunoblotting and immunohistochemistry techniques was used to characterize the expression pattern of pannexins in rat MCA. A fluorescent dye uptake approach in cultured smooth muscle cells was used to determine whether these cells have functional hemichannels. Results: We report for the first time that pannexins are expressed in the cerebral vasculature. We reveal that pannexin 1 is expressed in smooth muscle but not in endothelium and pannexin 2 is expressed in both endothelium and smooth muscle. Fluorescent dye entered cultured smooth muscle cells in the absence of extracellular calcium or when the cells were depolarized, which was prevented by the putative hemichannel blocker carbenoxolone. Conclusions: The identification of pannexins in rat MCA indicates that pannexin expression is not restricted to neuronal cells. Dye uptake in cultured smooth muscle cells exhibited properties similar to those of connexin and pannexin hemichannels, which may represent another form of cell-to-cell communication within the vasculature.

Connexin and pannexin signaling pathways, an architectural blueprint for CNS physiology and pathology?

“…As such, endothelial HCs provide a novel target to limit endothelial barrier disruption in inflammatory and ischemia-reperfusion conditions. More recently, Panx2 expression has been suggested to be present in endothelial cells in the rat middle cerebral artery [379], while Panx1 expression was identified in a human brain microvascular endothelial cell line [380]. Removal of extracellular calcium appeared to open both Cx43 HCs and Panx1 channels in the microvascular endothelial cells, which is in marked contrast to previous findings that Panx1 channels are insensitive to changes in [Ca 2? ]…”

A Comparative Antibody Analysis of Pannexin1 Expression in Four Rat Brain Regions Reveals Varying Subcellular Localizations

“…It is worth noting that Qiu et al (2011) and Santiago et al (2011) used the Ck4515 antibody to validate lack of expression in a Panx1 KO. Notably, two recent publications (Burns et al, 2012; Lohman et al, 2012) used immunoblotting, immunohistochemistry, and RT-PCR methods to cross-validate expression patterns in cerebral vasculature. However, it is important to remember that RT-PCR methods assay for mRNA expression, which can be different from protein expression.…”

Role of connexins and pannexins in cardiovascular physiology

“…However, as also noted by the authors, the physiological or pathophysiological relevance of CGRP-induced Panx1 channel opening remains to be determined [152]. Finally, Panx2 is expressed in the middle cerebral artery [153], but whether this or the expression of Panx3 in very small arteries has functional consequences is unknown.…”