The Role of Neuropeptide Y (NPY) and NPY Receptors on the [Ca2+]i Changes in Retinal Neural Cells

Abstract

Abstract: : Purpose: Neuropeptide Y (NPY) is a 36 amino acid peptide, and its effects are mediated through the activation of six G–protein–coupled receptors named NPY Y₁, Y₂, Y₃, Y₄, Y₅, and y₆. The aim of the present study was to investigate the role of NPY and NPY receptors on the [Ca²⁺]_i changes in rat retinal cell cultures. Methods: Rat retinal cells were obtained from newborn Wistar rats and cultured for 9 days. NPY–producing cells were identified by immunocytochemistry and the content of amidated–NPY was quantified by a sandwich–ELISA assay. The expression of NPY and its receptors was determined by RT–PCR. Single cell [Ca²⁺]i measurements were carried out with fura–2–AM fluorescence imaging. Results: The intracellular content of amidated–NPY in retinal cells was 1.4+0.1 fmoles NPY/million cells, and NPY was localised both in neurons and in glial cells. Retinal cells expressed mRNA for both NPY and NPY Y₁, Y₂, Y₄ and Y₅ receptors. NPY inhibited heterogeneously the increase in [Ca²⁺]_i evoked by 30 mM KCl in a concentration–dependent manner. The [Ca²⁺]_i increase was also inhibited by [Leu³¹Pro³⁴]NPY (Y₁/Y₄/Y₅ agonist), but not by NPY13–36 (Y₂ agonist). Conclusions:These results indicate that rat retinal cells synthesize NPY and express NPY Y₁, Y₂, Y₄ and Y₅ receptors. Also, NPY inhibits [Ca²⁺]_i changes in some cells through the activation of NPY Y₁, Y₄ or Y₅ receptor subtypes, thus modulating visual information processing in the retina.

Keywords: neuropeptides • second messengers • retinal culture