Galanin-receptor ligand M40 peptide distinguishes between putative galanin-receptor subtypes.
The galanin-receptor ligand M40 [galanin-(1-12)-Pro3-(Ala-Leu)2-Ala amide] binds with high affinity to [mono[125I]iodo-Tyr26]galanin-binding sites in hippocampal, hypothalamic, and spinal cord membranes and in membranes from Rin m5F rat insulinoma cells (IC50 = 3-15 nM). Receptor autoradiographic studies show that M40 (1 microM) displaces [mono[125I]iodo-Tyr26]galanin from binding sites in the hippocampus, hypothalamus, and spinal cord. In the brain, M40 acts as a potent galanin-receptor antagonist: M40, in doses comparable to that of galanin, antagonizes the stimulatory effects of galanin on feeding, and it blocks the galaninergic inhibition of the scopolamine-induced acetylcholine release in the ventral hippocampus in vivo. In contrast, M40 completely fails to antagonize both the galanin- mediated inhibition of the glucose- induced insulin release in isolated mouse pancreatic islets and the inhibitory effects of galanin on the forskolin- stimulated accumulation of 3',5'-cAMP in Rin m5F cells; instead M40 is a weak agonist at the galanin receptors in these two systems. M40 acts as a weak antagonist of galanin in the spinal flexor reflex model. These results suggest that at least two subtypes of the galanin receptor may exist. Hypothalamic and hippocampal galanin receptors represent a putative central galanin-receptor subtype (GL-1-receptor) that is blocked by M40. The pancreatic galanin receptor may represent another subtype ( GL-2-receptor) that recognizes M40, but as a weak agonist. The galanin receptors in the spinal cord occupy an intermediate position between these two putative subtypes.[1]References
- Galanin-receptor ligand M40 peptide distinguishes between putative galanin-receptor subtypes. Bartfai, T., Langel, U., Bedecs, K., Andell, S., Land, T., Gregersen, S., Ahrén, B., Girotti, P., Consolo, S., Corwin, R. Proc. Natl. Acad. Sci. U.S.A. (1993) [Pubmed]
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