Multiple neuropeptides exert a direct effect on the same isolated single smooth muscle cell.

The contractile effect of various neuropeptides was examined by pressure ejecting these agents from a pipette onto single smooth muscle cells freshly dissociated from the stomach of Bufo marinus. Substance P, cholecystokinin-octapeptide, and bombesin caused contraction, whereas vasoactive intestinal peptide, secretin, and dopamine inhibited acetylcholine-induced contractions. Acetylcholine and the three peptides which produced contraction were found in some instances to act on the same cell, suggesting that receptors for these agents exist on one and the same cell.