Stimulation of Phosphoinositide Hydrolysis by γ- and δ-Hexachlorocyclohexane in Primary Cultures of Cerebellar Granule Cells: Interaction with Glutamate and Carbachol Receptor-Mediated Phosphoinositide Response and Effects of Specific Pharmacological Agents

Abstract

The accumulation of [3H]inositol phosphates derived from phosphoinositide hydrolysis stimulated by γ- and δ-hexachlorocyclohexane isomers was characterized in primary cultures of cerebellar granule cells. The EC50for γ- and δ-hexachlorocyclohexane was 106 and 85 μM,respectively. Stimulatory effects of hexachlorocyclohexane isomers were highly dependent on extracellular Ca2+but they were not inhibited by classical voltage-sensitive Ca2+and Na+channel blockers. The Na+/Ca2+exchanger blocker amiloride caused a significant inhibition of δ-hexachlorocyclohexane effects. A lack of additive effects on phosphoinositide hydrolysis stimulation between hexachlorocyclohexane isomers and depolarization by high K+was observed. The effects of each hexachlorocyclohexane isomer on glutamate or carbachol-induced inositol phosphate stimulation were also not additive, whereas that of high K+was less than additive or synergistic when combined with glutamate or carbachol, respectively. When neuronal cells were exposed to the combination of δ-hexachlorocyclohexane and glutamate or carbachol in the presence of the respective receptor antagonists only the δ-hexachlorocyclohexane stimulatory effect was observed. Thus, the inhibition of glutamate- and carbachol-stimulated phosphoinositide hydrolysis by δ-hexachlorocyclohexane seems to imply a receptor-independent mechanism. It is suggested that both γ- and δ-hexachlorocyclohexane activate phosphoinositide-specific phospholipase C partly through Ca2+-related mechanisms.