Rapid down-regulation of substance P binding to guinea-pig pancreatic acinar cells during homologous desensitization.
Binding of 125I-labelled peptides, cytoplasmic Ca2+ concentration ([Ca2+]i) and amylase release were studied in guinea-pig pancreatic acinar cells during exposure to substance P (SP), and cholecystokinin octapeptide (CCK-8). Pre-incubation of cells at 22 degrees C with 0.03 nM to 1 microM SP for 10 min or at 37 degrees C for 5 min followed by acid or neutral washes reduced subsequent binding of 125I-Bolton-Hunter reagent-labelled SP (125I-BH-SP) in a biphasic manner by up to 95%. Incubation at 4 degrees C eliminated high-affinity binding of 125I-BH-SP and concentrations of SP above 1 nM were required for inhibition of subsequent tracer binding. Pre-incubation of cells at 37 degrees C with 1 nM to 1 microM CCK-8 for 10 min followed by neutral washes reduced subsequent binding of 125I-BH-CCK-8 by up to 65%. In cell suspensions, the [Ca2+]i response to SP was gradually reduced by pre-exposure to increasing agonist concentrations from 0.2 to 20 nM. Pre-incubation with high SP concentrations for 10 min caused profound reduction of subsequent amylase responses to SP, whereas secretion was little affected in corresponding experiments with CCK-8. Down-regulation of receptor binding is not important during short exposure to CCK-8, but it is a pronounced and rapid phenomenon during SP exposure, which explains tachyphylaxis of [Ca2+]i and amylase responses.
Sjödin
L
L
Pharmacological Division, Medical Products Agency, Uppsala, Sweden.
Viitanen
E
E
Gylfe
E
E
D000681:Amylases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008297:Male; D010179:Pancreas / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D012844:Sincalide / Q000494:pharmacology; D013373:Substance P / Q000378:metabolism*; D013388:Succinimides
C043194:Bolton Hunter reagent-substance P conjugate; D007457:Iodine Radioisotopes; D013388:Succinimides; D013373:Substance P; D000681:Amylases; D012844:Sincalide; D002118:Calcium