Cholinergic and peptidergic receptors on isolated human antral smooth muscle cells

Smooth muscle cells were isolated from segment so of human antrum obtained at operation. The presence, activity, and specificity of receptors to acetylcholine, the C-terminal octapeptide of cholecystokinin, methionine-enkephalin, and vasoactive intestinal peptide were examined. Muscarinic cholinergic receptors sensitive to low concentrations of atropine, cholecystokinin receptors sensitive to proglumide and dibutyryl cyclic guanosine monophosphate, enkephalin receptors sensitive to naloxone were demonstrated and found to mediate contraction. Vasoactive intestinal peptide receptors were demonstrated also and found to mediate relaxation. The stoichiometry and specificity of responses were closely similar to those previously found in isolated gastric smooth muscle cells of the guinea pig. The existence of high-affinity functional receptors on smooth muscle cells, together with the presence of the peptides in nerve terminals adjacent to these cells, makes it possible for these peptides to act as neurotransmitters.