The muscarinic receptor subtype in mouse pancreatic B-cells

Isolated mouse islets were used to identify the muscarinic receptor subtype present in pancreatic B-cells. We thus compared the inhibitory potencies of atropine (non-specific), of pirenzepine (specific for M 1 receptors) and of compound AF-DX 116 (specific for cardiac M 2 receptors) on acetylcholine-induced insulin release, 86Rb + efflux and 45Ca 2+ efflux. The three antagonists inhibited all effects of acetylcholine, but EC 50 values were markedly different: atropine = 1.5–5 nM, pirenzepine = 0.6–1.7 μM and AF-DX 116 = 1.7–11 μM. The results did not suggest that the various effects of ACh could result from the activation of different subtypes of receptors. It is concluded that muscarinic receptors of pancreatic B-cells belong to an M 2 subtype distinct from the cardiac M 2 receptors.