Pharmacological characterization of inositol-1,4,5,-trisphosphate binding to membranes from retina and retinal cultures

✍ Scribed by A.M. López-Colomé; I. Lee

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 747 KB
• Volume: 44
• Category: Article
• ISSN: 0360-4012
• DOI: 10.1002/(sici)1097-4547(19960415)44:2<149::aid-jnr7>3.0.co;2-d

✦ Synopsis

Light and excitatory amino acids (EAA) stimulate the phosphoinositide cycle in the vertebrate retina. The regulation of Ca2 + release from intracellular stores by inositol-1,4,5-trisphosphate (IP,) involves an interaction of this compound with specific receptors. By means of [3H]IP,-specific binding, we studied the kinetic and pharmacological properties of IP, receptors in the chick retina as well as in primary cultures of neurons and glia from this tissue. The equilibrium time for the binding reaction was 15 min and was optimal at alkaline pH (8.3). IP, receptor displayed high affinity (K,-40 nM) and selectivity for D-IP,, compared to D-IP, > L-IP, > D-IP, > D-IP,. These characteristics were the same in subcellular fractions from outer (PI) and inner (Pz) plexiform layers, binding sites being more abundant in P, (2.65 pmoVmg protein) than in P, (0.82 pmol/mg protein). IP, receptors were present in both neuronal and glial cultures, but were concentrated in neuronal cultures. Binding was not affected by ryanodine, or caffeine, related to calcium-induced calcium release (CICR) channels, nor by the endoplasmic reticulum Ca2+ ATPase inhibitor thapsigargin, while heparin effectively inhibited IP, binding. GSSG and thimerosal increased the affinity of [,H]IP, binding from IC,, -80 nM to IC,, -40 nM; this effect was reversed by DTT. Binding in zero Caz+ was decreased by low concentrations of Ca2+ (350 nM). These results suggest that actions of IP, in the retina are regulated by physiological changes in intracellular pH and Ca2+ concentrations, as well as by the oxidation state of the receptor. Additionally, the presence of IP, receptors in Miiller glia opens the possibility of IP, participation in nonsynaptic signalling through Ca2+ waves in