Phospholipase C activation by ethanol in rat hepatocytes is unaffected by chronic ethanol feeding

Abstract

The activation of phosphoinositide-specific phospholipase C by ethanol was compared in hepatocytes isolated from ethanol-fed rats and from pair-fed control animals. Ethanol (100-300 mM) caused a dose-dependent transient increase in cytosolic free Ca2+ levels in indo-1-loaded hepatocytes from both groups of animals. The rate of Ca2+ increase was similar in hepatocytes from control and ethanol-fed rats, but the decay of the Ca2+ increase was somewhat slower in the latter preparation. The ethanol-induced Ca2+ increase caused activation of glycogen phosphorylase, with 50% response at 50 mM-ethanol and a maximal response at 150-200 mM-ethanol, not significantly different in hepatocytes from control and ethanol-fed animals. Ins(1,4,5)P3 formation in response to ethanol (300 mM) or vasopressin (2 nM or 40 nM) was also similar in the two preparations. It is concluded that long-term ethanol feeding does not lead to an adaptive response with respect to the ethanol-induced phospholipase C activation in rat hepatocytes. The ability of ethanol in vitro to decrease membrane molecular order in liver plasma membranes from ethanol-fed and control rats was measured by e.s.r. Membranes from ethanol-fed animals had a significantly lower baseline order parameter compared with control preparations (0.313 and 0.327 respectively), indicative of decreased membrane molecular order. Addition of 100 mM-ethanol significantly decreased the order parameter in control preparations by 2.1%, but had no effect on the order parameter of plasma membranes from ethanol-fed rats, indicating that the plasma membranes had developed tolerance to ethanol, similar to other membranes in the liver. Thus the membrane structural changes associated with this membrane tolerance do not modify the ethanol-induced activation of phospholipase C. The transient activation of phospholipase C by ethanol in hepatocytes may play a role in maintaining an adaptive phenotype in rat liver.

The Effects of Chronic Ethanol Consumption During Early Pregnancy on Conceptus Health and Uterine Function in Pigs

“…Similar results were found for ventricular myocardiocytes that were exposed to ethanol chronically (Piano and Schwertz, 1997). In contrast, prostaglandin concentration was shown to increase in the cerebral cortex of fetal sheep after acute ethanol exposure (Reynolds et al, 1997), whereas studies with hepatocytes indicated that cellular signaling involved in prostaglandin synthesis is not affected by chronic ethanol exposure (Hoek et al, 1990). Contradictory results among the previously described studies may be a function of the level and pattern of ethanol exposure or differences in tissue-specific responses to alcohol.…”

Chronic ethanol administration to rats decreases receptor-operated mobilization of intracellular ionic calcium in cultured hepatocytes and inhibits 1,4,5-inositol trisphosphate production: relevance to impaired liver regeneration.

“…Further, recent work by Spitzer has demonstrated that 8 wk ethanol feeding in rats impairs the PLC-linked generation of inositol polyphosphates induced in rat liver by vasopressin (53). In contrast, Hoek et al (54) reported that a 5-7 wk period of ethanol consumption did not affect hepatic PLC activity. The explanation for these differences may lie in the dose and duration of alcohol exposure.…”

Effect of Chronic Ethanol Exposure on Myocardial Phosphoinositide Turnover

“…For example, Gonzales and Crews17 demonstrated that chronic ethanol exposure (5 months) had no effect on norepinephrine-elicited phosphoinositide hydrolysis in brain slices. Likewise, Hoek et al 41 found that 5-7 weeks of ethanol feeding had no effect on vasopressin-and other agoniststimulated phosphoinositide turnover in rat hepatocytes. In contrast, Hoffman et al" found that chronic ethanol treatment (7 days and 24 hr of withdrawal) decreased the EC,, for carbachol-induced phosphoinositide hydrolysis in brain slices.…”