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It is known that the human exocrine pancreas responds to secretin stimulation more than does VIP, a structurally related peptide. We looked for the receptors for those polypeptides in a human pancreatic cancer cell line grown in culture and in nude mice. By analysing the cAMP responses and the 125I-VIP binding we found VIP receptors with a KD of 1.5 10(-9) M. Secretin stimulates the adenylate cyclase through the VIP receptor sites with a KD of 1.7. 10(-6) M. We noted also that during cell proliferation in culture there was about a 5 fold increase of the cAMP response to VIP.

The binding of bombesin to its receptors on normal human pancreatic membranes was investigated using high specific activity, radioiodinated bombesin ([125I]-Tyr4-bombesin), prepared by an oxidative method with chloramine-T. Binding was specific, temperature-dependent, saturable, reversible and linearly related to membranes protein concentration. After a 30 min period of incubation with membranes the degradation of the tracer has never been found superior to 20%. Scatchard analysis of binding data was compatible with a single class of binding sites with a high affinity (0.96 nM) and a Bmax of 753 fmol/mg protein. [125I]-Tyr4-bombesin binding to human pancreatic membranes was competitively inhibited by (1-Tyr4-)bombesin, GRP, the nonapeptide of bombesin and litorin but not by unrelated hormones such as somatostatin, CCK, human gastrin, etc. These results describe for the first time the presence of specific receptors for bombesin on human pancreatic membranes. The binding characteristics obtained are comparable with those found in other species.

VIP and secretin control the secretory function of the normal pancreas. We analysed their regulatory functions in a human pancreatic cancer cell line: Capan-1. Saturation binding experiments with 125I-VIP showed the existence of one class of binding sites of very high affinity: KD 6.4 +/- 3.0 X 10(-11) M and a low Bmax: 12 fmoles/10(6) cells, in both intact cells and membrane preparations. This site has not yet been described in normal or tumorous digestive cells. Competition binding experiments let us characterize two more binding sites, KD: 2.1 +/- 0.7 X 10(-9) M and 5.0 +/- 0.6 X 10(-8) M and the corresponding Bmax: 120 and 500 fmoles/10(6) cells. These sites are similar to those found on cells of the digestive tract. Competition binding experiments gave the following IC50: 3.0 +/- 0.9 X 10(-9) M for VIP; 2 +/- 0.6 X 10(-6) M for PHI; and 1 +/- 0.7 X 10(-5) M for secretin. VIP elicited a cAMP rise, the half maximal response being obtained at 1.2 X 10(-10) M. Secretin induced a cAMP response but only for concentrations higher than 10(-8) M. VIP receptors were found to be modulated by two factors: cell ageing and cell density. Cells chronically treated with VIP showed a slight decrease of their proliferation; insulin exerted an opposite effect. It is concluded that at the difference of normal pancreatic cells, the present cell line lacks secretin-preferring receptors and acquires some of the properties of intestinal cells.