Connexins and M3 Muscarinic Receptors Contribute to Heterogeneous Ca2+ Signaling in Mouse Aortic Endothelium

Abstract

Background/Aims: Smooth muscle tone is controlled by Ca²⁺ signaling in the endothelial layer. Mouse endothelial cells are interconnected by gap junctions made of Connexin40 (Cx40) and Cx37, which allow the exchange of signaling molecules to coordinate their activity. Here, we investigated the role of Cx40 in the endothelial Ca²⁺ signaling of the mouse aorta. Methods: Ca²⁺ imaging was performed on intact aortic endothelium from both wild type (Cx40+/+) and Connexin40-deficient (Cx40 -/-) mice. Results: Acetylcholine (ACh) induced early fast and high amplitude Ca²⁺ transients in a fraction of endothelial cells expressing the M3 muscarinic receptors. Inhibition of intercellular communication using carbenoxolone or octanol fully blocked the propagation of ACh-induced Ca²⁺ transients toward adjacent cells in WT and Cx40-/- mice. As compared to WT, Cx40-/- mice displayed a reduced propagation of ACh-induced Ca²⁺ waves, indicating that Cx40 contributes to the spreading of Ca²⁺ signals. The propagation of those Ca²⁺ responses was not blocked by suramin, a blocker of purinergic ATP receptors, indicating that there is no paracrine effect of ATP release on the Ca²⁺ waves. Conclusions: Altogether our data show that Cx40 and Cx37 contribute to the propagation and amplification of the Ca²⁺ signaling triggered by ACh in endothelial cells expressing the M3 muscarinic receptors.