Effects of Vasoactive Intestinal Peptide and Other Peptides on Cyclic AMP Accumulation in Intact Pieces and Isolated Horizontal Cells of the Teleost Retina

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Abstract
The effects of vasoactive intestinal peptide (VIP) and several other peptides have been examined on cyclic AMP accumulation in intact pieces and isolated horizontal cells of the teleost (carp) retina. VIP was the most effective peptide examined, inducing a dose‐related response, and an approximately fivefold increase in cyclic AMP production when used at a concentration of 10 μM. Porcine histidine isoleucine‐containing peptide and secretin, peptides structurally related to VIP, also stimulated cyclic AMP accumulation, but at concentrations of 10 μM induced responses which were only approximately 40% and 10%, respectively, of the response observed with 10 μM VIP. In contrast, several other peptides, including glucagon, neurotensin, somatostatin, luteinizing hormone‐releasing hormone, α‐melanocyte‐stimulating hormone, cholecystokinin octapeptide26–33, gastrin‐releasing peptide, thyrotropin‐releasing hormone, and VIP10–28 were totally inactive. The response to 10 μM VIP was not antagonized by several dopamine antagonists, indicating the presence of a population of specific VIP receptors coupled to adenylate cyclase, distinct from the population of dopamine receptors coupled to adenylate cyclase also known to be present in this tissue. Finally, experiments involving the use of fractions of isolated horizontal cells indicate that these neurons possess a population of VIP receptors coupled to cyclic AMP production which would appear to share a common pool of adenylate cyclase with a population of similarly coupled dopamine receptors. These data are discussed in terms of the presence, localization, and possible function of a putative VIP‐ergic innervation in the carp retina.