Functional characterization of a muscarinic receptor in the smooth muscle of the shark (Squalus acanthias) ventral aorta

Abstract

A suite of muscarinic receptor blockers was used to characterize the receptor(s) mediating the contractile effect of acetylcholine (ACh) on isolated rings of ventral aorta from the dogfish shark, Squalus acanthias. The M2/M4-specific inhibitor N,N’-bis(6-{[(2-methoxyphenyl) methyl] amino} hexyl) -1,8- octane diamine tetrahydrochloride (methoctramine) did not reduce the efficacy of ACh, and the M3-specific inhibitor 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) displaced the ACh concentration-response curve to the right at much lower concentrations than the M1-specific inhibitor (5-11-dihydro-11- [4-methyl-l-piperazinyl)acetyl] -6H-pyrido[2,3-b] [1,4] benzodiazepin-6-one dihydrochloride) (pirenzepine). It appears, therefore, that an M3-type muscarinic receptor is expressed in the aortic vascular smooth muscle of the dogfish shark.