Cholecystokinin-induced inhibition of endocytosis of receptor-bound substance P in pancreatic acinar cells.
Association of 125I-Bolton-Hunter labelled substance P (125I-BH-SP) to suspended pancreatic acinar cells of the guinea pig was studied. Cellular association at 37 degrees C and 22 degrees C was inhibited by cholecystokinin octapeptide (CCK-8) in concentrations from 10(-9) to 10(-6)M, whereas another pancreatic secretagogue, carbachol, was uneffective. The CCK induced inhibition disappeared at low temperatures. CCK-8 mainly interfered with internalization of 125I-BH-SP into acinar cells. Increased extracellular Ca2+ and the Ca2+ ionophores A23187 and ionomycin reduced association of 125I-BH-SP to cells whereas extracellular Ca2+ chelation with EGTA had the opposite effect. However, extra- and intracellular Ca2+ chelation did not affect the degree of CCK-induced reduction of 125I-BH-SP association to acinar cells but eliminated the effect of the calcium ionophore ionomycin. Three agents known to interfere with receptor recycling, namely monensin, methylamine and ammonium chloride reduced cell-associated 125I-BH-SP. In a series of experiments, the cytoplasmic calcium concentrations ([Ca2+]i) during exposure to these three agents, to the CCK-8-analogue caerulein and to ionomycin were determined. In all cases, [Ca2+]i was raised. The results indicate that endocytosis of receptor-bound 125I-BH-SP is regulated by CCK and that the endocytotic process is influenced by calcium.
Sjödin
L
L
Pharmacological Division, Medical Products Agency, Uppsala, Sweden.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002469:Cell Separation; D002766:Cholecystokinin / Q000494:pharmacology*; D004705:Endocytosis / Q000187:drug effects*; D016257:Fura-2; D006168:Guinea Pigs; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D008566:Membranes / Q000378:metabolism; D010179:Pancreas / Q000166:cytology / Q000187:drug effects*; D011869:Radioligand Assay; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism*; D013696:Temperature
D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter; D013373:Substance P; D000001:Calcimycin; D015759:Ionomycin; D002766:Cholecystokinin; D002118:Calcium; D016257:Fura-2