A clonal rat pancreatic δ cell line (Rin 4B) expresses a high number of galanin receptors negatively coupled to a pertussis‐toxin‐sensitive cAMP‐production pathway

Galanin, an ubiquitous neuropeptide, was recently shown to inhibit somatostatin release by the rat islet tumor cell line, Rin‐m. By using the clonal pancreatic delta cell line Rin14B, originating from Rin‐m cells, we were able to identify the presence of one type of specific galanin‐binding site of high affinity ( K d = 1.6 nM; maximal binding capacity = 270 fmol/mg protein) and high specificity for the peptide. Binding of 125 I‐galanin to these receptors was time‐dependent and highly sensitive to guanine nucleotides. Using the cross‐linker disuccinimidyl tartarate, covalent linking of the galanin receptor to 125 I‐galanin in membranes from Rin14B cells, followed by SDS/PAGE analysis of membrane proteins, indicated that the galanin receptor is a protein of 54 kDa. 0.1–100 nM galanin also exerted a marked inhibitory effect on the cAMP‐production system under basal conditions, as well as in the presence of the pancreatic peptide glucagon. At a maximal dose, galanin induces a 90–100% decrease of basal and glucagon‐stimulated cAMP production levels, with a median inhibition concentration (IC 50 ) of 3 nM galanin. The direct inhibitory effect of galanin on the adenylate cyclase activity in Rin14B cell membranes was also demonstrated (IC 50 = 3 nM galanin). The inhibitory effect of galanin on the basal and glucagon‐stimulated cAMP production in Rin14B cells was reversed by pertussis toxin. The toxin was also shown to specifically ADP‐ribosylate a protein of 41kDa in membranes from Rin14B cells. Taken together, these data show that the pancreatic delta cell line Rin14B expresses high affinity galanin receptors negatively coupled to a pertussis‐toxin‐sensitive cAMP‐production system.