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Depolarization and Activation of Dihydropyridine‐Sensitive Ca 2+ Channels Stimulate Inositol Phosphate Accumulation in Photoreceptor‐Enriched Chick Retinal Cell Cultures
Author(s) -
Gan Jiwei,
Iuvone P. Michael
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.68062300.x
Subject(s) - inositol phosphate , inositol , nitrendipine , phospholipase c , dihydropyridine , inositol trisphosphate , pertussis toxin , biology , voltage dependent calcium channel , stimulation , calcium , chemistry , endocrinology , biochemistry , biophysics , g protein , receptor , organic chemistry , blood pressure
Elevated concentrations of extracellular K + increased inositol phosphate accumulation in primary cultures of chick retinal photoreceptors and multipolar neurons. K + ‐evoked stimulation of inositol phosphate accumulation was greater in photoreceptor‐enriched cell cultures than in cultures where multipolar neurons were the predominant cell type. Destroying multipolar neurons, but not photoreceptors, with kainic acid and N ‐methyl‐ d ‐aspartate did not reduce the K + ‐evoked stimulation of inositol phosphate accumulation. Both of these observations indicate that the observed effects occur in photoreceptor cells. The K + ‐evoked stimulation of inositol phosphate accumulation was blocked by omitting Ca 2+ from the incubation medium or by adding the dihydropyridine‐sensitive Ca 2+ ‐channel antagonists, nitrendipine and nifedipine. Bay K 8644, a dihydropyridine agonist, stimulated inositol phosphate accumulation and enhanced the effect of K + . ω‐Conotoxin GVIA, an inhibitor of N‐type Ca 2+ channels, had no significant effect on K + ‐stimulated inositol phosphate accumulation. Pretreatment with pertussis toxin neither blocked K + ‐evoked inositol phosphate accumulation nor altered the inhibitory effect of nifedipine. K + ‐evoked inositol phosphate accumulation appears to reflect activation of phosphatidylinositol‐specific phospholipase C, as it is inhibited by U‐73122. These results indicate that Ca 2+ influx through voltage‐gated, dihydropyridine‐sensitive channels activates phospholipase C in photoreceptor inner segments and/or synaptic terminals.