In this work, we studied a novel chimeric peptide, M242, galanin(1–13)-[d-Trp32]-neuropeptide Y(25–36)amide, and examined its properties in comparison with its parent peptide, M32, galanin(1–13)-neuropeptide Y(25–36)amide, a previously known high-affinity ligand for galanin receptors, and galanin itself. Binding assays performed in Bowes cells known to express human galanin receptor type 1 (hGalR1) and in Chinese hamster ovary cells overexpressing human galanin receptor type 2 (hGalR2) revealed that all three ligands had comparable affinities: at hGalR1<1 nM and at hGalR2<10 nM. However, in rat hippocampal membranes M242 had a 24-fold lower affinity than galanin (9.4 vs. 0.4 nM) and 134-fold lower affinity than M32 (9.4 vs. 0.07 nM). In the same tissue, we also examined the effects of these peptides on adenylate cyclase activity. M32 showed a weak antagonistic behaviour but M242 acted as a potent biphasic regulator of adenylate cyclase. In conclusion, we present and characterise a new peptide M242, which could be a useful tool in studies of galaninergic signalling.

The chimeric peptides consisting of galanin(l-13) and C-terminus of bradykinin, M35, M58 and M59, inhibit the level of basal adenylate cyclase activity in rat ventral hippocampal membranes in a complex way. At certain concentrations, M35 (0.1-10 nM), M59 (0.1-1000 nM) and M58 (100-10000nM) antagonize the inhibitory effect of galanin on basal activity of the ventral hippocampal adenylate cyclase. All three chimeric peptides are high-affinity ligands at ventral hippocampal galanin receptors with Hill coefficients significantly less than unity. The involvement of distinct binding sites in the biphasic regulation of adenylate cyclase activity by these chimeric galanin analogues in ventral hippocampal membranes has been suggested.