Two modes of regulation of the phospholipase C-linked substance-P receptor in rat parotid acinar cells.
In rat parotid acinar cells prelabelled with [3H]inositol, substance P (100 nM) induced the formation of [3H]inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. Ins(1,4,5)P3 reached a maximum 7 s after substance P stimulation, and thereafter decreased and reached a stable value at 60 s. When the cells were exposed to substance P for 10, 30, 60, or 300 s, washed, and re-exposed to this peptide, the formation of [3H]inositol trisphosphate (InsP3) was attenuated in a time-dependent manner. In the cells pretreated as described above, the number of [3H]substance-P-binding sites (Bmax) was also decreased. Possible role(s) of Ca2+ and protein kinase (protein kinase C) control mechanisms in regulating substance P responses were investigated. Desensitization of substance P-induced InsP3 was not affected by the Ca2+ ionophore ionomycin, nor was it dependent on Ca2+ mobilization. On the other hand, in the presence of 4 beta-phorbol 12,13-dibutyrate (PDBu) and 12-O-tetradecanoyl-4 beta-phorbol 13-acetate, known activators of protein kinase C, substance P-induced InsP3 formation was inhibited. However, PDBu had no effect on [3H]substance P binding, whether present during the assay or when cells were pretreated. The persistent desensitization of InsP3 formation induced by substance P was not affected by PDBu. These results suggest that the persistent desensitization of InsP3 formation induced by substance P is a homologous process involving down-regulation of the substance P receptor; the mechanism does not appear to involve, or to be affected by, the Ca2+ or protein kinase C signalling systems. Protein kinase C activation can, however, inhibit substance P-induced InsP3 formation, which may indicate the presence of a negative-feedback control on the substance P pathway.
Sugiya
H
H
Laboratory of Cellular and Molecular Pharmacology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709.
Obie
J F
JF
Putney
J W
JW
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism; D010306:Parotid Gland / Q000187:drug effects / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013373:Substance P / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*
D007295:Inositol Phosphates; D010703:Phorbol Esters; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter; C008876:phorbol-12,13-didecanoate; D013373:Substance P; D015240:Phorbol 12,13-Dibutyrate; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium