Different receptors mediate the action of bombesin-related peptides on gastric smooth muscle cells.

Recent studies suggest that different subtypes of receptors may mediate the action of various bombesin-related peptides in different tissues. In the present study the ability of bombesin and its structurally related peptides [litorin, gastrin-releasing peptide (GRP), GRP18-27, neuromedin B, [Leu8]litorin, and bombesin nonapeptide BN(6-14)] to interact with smooth muscle cells isolated from guinea pig stomach was investigated. Each peptide induced a specific contractile response with potencies (D50 in pM) of [Leu8]litorin (0.7) greater than bombesin (1.2) greater than litorin (3) greater than neuromedin B (3.5) = GRP (3.8) = GRP18-27 (3.9) greater than BN(6-14) (70.9). The specific bombesin receptor antagonist psi 13,14-bombesin differed in its potency for inhibiting equipotent concentrations of bombesin, GRP, or neuromedin B, was equipotent for bombesin or GRP (IC50 12.7 and 22.1 nM), and was 11 times less potent for neuromedin B (IC50 234.5 nM), suggesting the presence of subtypes of receptors mediating the action of bombesin-related peptides. To further investigate this possibility, a technique of receptor protection that enables selective preservation of one receptor type was used. GRP or bombesin protected completely the response to GRP or bombesin but abolished the subsequent contractile response to neuromedin B. Neuromedin B, instead, protected only the response to neuromedin B. These results demonstrate that gastric smooth muscle cells possess specific receptors that interact with bombesin-related peptides and that two receptor subtypes mediate the contractile response to these peptides: one subtype is selective for bombesin or GRP, the other for neuromedin B.