Regulation of Cholecystokinin Secretion by Peptones and Peptidomimetic Antibiotics in STC-1 Cells

Abstract

Peptones are potent stimulants of cholecystokinin (CCK) release in rats, both in vivo and ex vivo in a model of isolated vascularly perfused duodeno-jejunum preparation and in vitro in the intestinal CCK-producing cell line STC-1. The underlying mechanisms were here investigated with this cell line. Protein hydrolysates from various origins (meat, casein, soybean, and ovalbumin; 0.5–1%, wt/vol) dose dependently increased CCK release. Cephalosporin antibiotics, which mimic tripeptides, also stimulated the release of CCK over the concentration range 1–20 mm. The study of concentration dependence of cephalosporin uptake indicated a passive diffusion process at either pH 7.4 or pH 6.0, thus arguing against the involvement of a peptide transporter in CCK secretion. After pertussis toxin treatment (200 ng/ml; 5 h), the peptone- and cephalexin-induced CCK secretion was significantly reduced, suggesting the involvement of pertussis toxin-sensitive heterotrimeric G protein(s) in the secretory activity of STC-1 cells. Consistent with this was the identification by Western blot of Gi2α, Gi3α, and Goα immunoreactivities in STC-1 cell extracts. Additionally, peptones and cephalexin increased the cellular content in inositol phosphates, whereas a mild increase in cAMP content was restricted to peptone-treated cells. Protein kinase A or C inhibition did not modify peptone- or antibiotic drug-evoked CCK release. The extracellular Ca2+ chelator EGTA (500 μm) and the intracellular Ca2+ chelator BAPTA-AM[ 1,2-bis-(O-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetra(acetoxymethyl) ester; 20 μm] abolished the peptone- and antibiotic drug-induced CCK release. Nifedipine and verapamil (10 μm) reduced by about 50% the CCK secretion evoked by these two secretagogues. In conclusion, peptones and some cephalosporins are potent stimulants of CCK release in the STC-1 cell line. The cellular mechanisms involve pertussis toxin-sensitive G protein(s) and are dependent on Ca2+ availability. We suggest that the STC-1 cell line is a useful model to study the molecular basis of peptone-induced CCK secretion.