Blockade of galanin-induced inhibition of insulin secretion from isolated mouse islets by the non-methionine containing antagonist M35

Abstract The neuropeptide galanin occurs in pancreatic adrenergic nerves and has been suggested to be the adrenergic mediator of the stress-induced inhibition of insulin release. To study its physiological fucntion, we recently synthesized a galanin-like galanin receptor antagonist, galantide. However, this antagonist contains a methionine moiety, and is therefore easily oxidized. We have now synthesized another galanin antagonist which does not containe methione. This peptide, M35, is a chimeric 21 amino acid peptide in which galanin-(1–13) is coupled to bradykinin-(2–9). M35 (10 μM to 1 pM) had no effect by itself on glucose (11.1 nM)-stimulated insulin secretion in isolated mouse islets, but potently counteracted the inhibitory action of galanin (100 nM). The lowest effective dose of M35 was 10 nM. M35 did not counteract the inhibitory action of clonidine (1 μM) or somatostatin (1 μM) on insulin secretion. Furthermore, M35 displaced 125 I-monoiodo-[Tyr 26 ]galanin from membranes of insulin producing RINm5F cells. The displacement curve fitted to a two-site model in which 60% of label bound with a K 1 of 0.1 ± 0.01 nM and 40% with a K 2 of 3 ± 0.5 nM. In conclusion, M35 is a specific, non-methionine-containing galanin receptor antagonist on insulin-producing cells.