Muscarinic receptor knockout mice confirm involvement of M3 receptor in endothelium-dependent vasodilatation in mouse arteries

The aim of the study was to determine which cholinergic muscarinic receptor subtype is responsible for the endothelium-dependent vasodilatation evoked by acetylcholine (ACh) in mouse arteries. Endothelium-dependent relaxations were evaluated using isometric tension measurement of ring from femoral and aortic artery of M-1, M-2, and M-3 knockout (KO) mice. Rings of femoral and aortic artery from M-3 KO mice did not exhibit relaxation at the opposite of rings from M-1+M-2 KO and wild-type (WT) mice, which were relaxed by ACh. The proportion of endothelial cells responsive to ACh, as manifested by an increase in cytosolic free calcium ([Ca2+](i)), was also observed on the intima of aorta wall in vitro by using laser line confocal microscopy Of the cells from M-3 KO mice and M-1+M-2 KO mice, 4% and 23%, respectively, responded to ACh in comparison with 20 % in WT mice. These results show that in the endothelium from femoral and aortic artery, the larger proportion of cells that express M-3 receptor is responsible for the specificity of the M-3 receptor subtype for endothelium-dependent relaxation caused by ACh.