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Identification of Glucagon Receptors in Rat Retina

1990; Wiley; Volume: 54; Issue: 4 Linguagem: Inglês

10.1111/j.1471-4159.1990.tb01953.x

1471-4159

R. Fernández‐Durango, Didier Sanchez, A Fernández‐Cruz,

Diabetes Treatment and Management

Abstract: In this study, we characterize the glucagon receptors on rat retinal particulate preparations. The specific binding of 125 I‐glucagon was saturable and reversible. Apparent equilibrium conditions were established within 30–45 min. Analysis of binding data is compatible with the existence of two classes of binding sites: a high‐affinity class with a K D of 7 ± 0.8 n M and a B max of 2.3 ± 0.2 pmol/mg of protein and a low‐affinity class with a K D of 84.4 ± 2.5 n M and a B max of 16.5 ± 2.3 pmol/mg of protein. The 125 I‐glucagon binding to retinal particulate preparation was not inhibited by 1 μ M concentrations of insulin, atrial natriuretic factor, angiotensin II, somatostatin, and vasoactive intestinal peptide. However, synthetic human pancreatic growth hormone‐releasing factor, hGRF‐44, inhibited binding, although the concentration required for half‐maximal displacement was 10‐fold higher than that for native glucagon. Glucagon binding was GTP sensitive. Inclusion of 0.1 m M GTP in the binding assay produced an increase in the concentration of unlabeled glucagon required for half‐maximal displacement of 125 I‐glucagon, from 23 to 220 n M . Glucagon stimulated adenylate cyclase formation in retinal particulate preparations. The concentration of glucagon required for half‐maximal activation of retinal adenylate cyclase was 16.2 n M . These results suggest that glucagon may play a role as a neurosignal transmitter in rat retina.