[3H]inositol trisphosphate specific binding in two brain regions of long and short sleep mice

Ethanol alters the inhibitory effect of calcium ions on [(3) H]-inositol 1,4,5-trisphosphate binding

In this study we have analysed the effects of ethanol and divalent cations on the binding of [(3) H]-inositol 1,4,5 trisphosphate to rat cerebellar membranes. Rats were injected intraperitoneally, daily, with 3g of ethanol/kg of body weight for different periods of time. Repeated in vivo administration of ethanol caused a reduction of about 30% of binding in an in vitro assay carried out in the presence of 1 mM EDTA. With an IC approximately 250 nM calcium ions produced a reduction in binding to cerebellar membranes isolated from control rats. The inhibitory effect was not observed in membranes taken from animals injected with alcohol for 21 days. Magnesium and manganese ions also lowered IP binding. The metabolic degradation of IP to IP was increased by magnesium and manganese but not by calcium and was similar in control and ethanol 2 treated rats. The results indicate that ethanol repeatedly administered to rats modifies the sensitivity of the IP receptor to calcium ion, but that it does not alter the metabolic fate of IP to IP. This supports the idea that ethanol may have preferable targets within the cell.

Effect of chronic ethanol treatment and selective breeding for sensitivity to ethanol on calcium release induced by inositol trisphosphate or ethanol from brain and liver microsomes

Our previous work showed that ethanol increases the resting intracellular free calcium concentration (CAi) in synaptosomes and releases calcium from an inositol trisphosphate (IP3)-insensitive calcium store of brain microsomes. In this report, we investigated the effects of chronic ethanol treatment and selective breeding for hypnotic sensitivity to ethanol on IP3 and ethanol-stimulated calcium release from brain and liver microsomes. Chronic ethanol treatment did not alter IP3-stimulated calcium release from brain microsomes or ethanol-stimulated calcium release from brain or liver microsomes. Chronic ethanol treatment increased the spontaneous release of calcium from brain but not liver microsomes. In microsomes isolated from cerebellum or cerebral cortex of long-sleep (LS) and short-sleep (SS) mice, ethanol and IP3 released calcium in a concentration dependent manner. The amount of calcium released by ethanol and IP3 was larger in microsomes isolated from cerebellum than microsomes from cerebral cortex. However, the amount of calcium released by ethanol and IP3 did not differ between the two lines in either brain area. These results do not support the idea that the hypnotic effects of ethanol are due to ethanol-induced calcium release from a nonmitochondrial intracellular calcium store in brain tissue. The development of ethanol tolerance and dependence also does not appear to be associated with altered ability of ethanol to release calcium from non-mitochondrial intracellular stores; however, effects of chronic ethanol exposure on spontaneous release of intracellular calcium could alter neuronal function in ethanol dependence.

Differential effects of norepinephrine on phosphatidylinositol 4,5-bisphosphate stimulated hydrolysis in brains of mice genetically selected for differences in ethanol sensitivity

The effects of norepinephrine on phosphoinositide turnover were evaluated in five brain regions of the long sleep (LS) and short sleep (SS) mice. These mice were selectively bred for differences in central nervous system sensitivity to ethanol with the LS exhibiting much greater sensitivity to a hypnotic dose of ethanol than the SS, as determined by the ability of the mice to regain their righting reflex. Norepinephrine (10(-3) M, 10(-4) M, and 10(-5) M) significantly increased phosphoinositide turnover in the hippocampus, hypothalamus, locus ceruleus, cerebellum, and cortex within each line of mice. Basal and norepinephrine-stimulated phosphoinositide turnover were significantly higher in the SS mice as compared with the LS mice in the cerebellum and cortex but not the other brain regions. Incorporation of 3H-inositol into 3H-phosphatidylinositols was not different between SS and LS mice in the cerebellum and cortex. The greater norepinephrine-stimulated phosphoinositide turnover in the cerebellum and cortex of the SS versus the LS mice may contribute to the CNS sensitivity to ethanol in these two lines of mice. However, ethanol (500 mM) had no effect on basal or norepinephrine-stimulated phosphoinositide turnover in any of the five brain areas examined in the LS and SS mice.