title: Homologous desensitization of substance-P-induced inositol polyphosphate formation in rat parotid acinar cells.
abstract: Maximal concentrations of substance P and methacholine induced a rapid increase in [3H]inositol trisphosphate ([3H]IP3) formation. After about 1 min, the [3H]IP3 in the substance-P-treated cells ceased to increase further, whereas in the methacholine-treated cells [3H]IP3 continued to increase. Addition of methacholine to the substance-P-treated cells caused a rapid increase in [3H]IP3, whereas a second addition of a 10-fold excess of substance P had no effect. Pretreatment of cells with substance P, followed by removal of the substance P by washing, resulted in a decreased response to a second application of substance P. A similar protocol involving pretreatment with methacholine had no effect on subsequent responsiveness to substance P. Analysis of [3H]substance P binding to substance-P-treated cells indicated that the number of receptors for substance P was decreased, but the affinity of the receptors for substance P was unaffected. After substance P pretreatment, a prolonged incubation (2 h) restored responsiveness of the cells to substance P, measured as [3H]IP3 formation, and restored the number of binding sites to control values. These findings indicate that, in the rat parotid gland, substance P induces a homologous desensitization of its receptor, which involves a slowly reversible down-regulation or sequestration of substance-P-binding sites.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000096:biosynthesis*; D007700:Kinetics; D008297:Male; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D010306:Parotid Gland / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter / Q000378:metabolism; D013373:Substance P / Q000494:pharmacology*; D013403:Sugar Phosphates / Q000096:biosynthesis*
chemical_list: D007295:Inositol Phosphates; D008688:Methacholine Compounds; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter; D013403:Sugar Phosphates; D016210:Methacholine Chloride; D013373:Substance P; D015544:Inositol 1,4,5-Trisphosphate