Ethanol stimulates glucose uptake and translocation of GLUT-4 in H9c2 myotubes via a Ca²⁺-dependent mechanism

Abstract

Short-term exposure to ethanol impairs glucose homeostasis, but the effects of ethanol on individual components of the glucose disposal pathway are not known. To understand the mechanisms by which ethanol disrupts glucose homeostasis, we have investigated the direct effects of ethanol on glucose uptake and translocation of GLUT-4 in H9c2 myotubes. Short-term treatment with 12.5-50 mM ethanol increased uptake of 2-deoxyglucose by 1.8-fold in differentiated myotubes. Pretreatment of H9c2 myotubes with 100 nM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, had no effect on ethanol-induced increases in 2-deoxyglucose uptake. In contrast, preincubation with 25 microM dantrolene, an inhibitor of Ca(2+) release from the sarcoplasmic reticulum, blocked the stimulation of 2-deoxyglucose uptake by ethanol. Increased 2-deoxyglucose uptake after ethanol treatment was associated with a decrease in small intracellular GLUT-4 vesicles and an increase in GLUT-4 localized at the cell surface. In contrast, ethanol had no effect on the quantity of GLUT-1 and GLUT-3 at the plasma membrane. These data demonstrate that physiologically relevant concentrations of ethanol disrupt the trafficking of GLUT-4 in H9c2 myotubes resulting in translocation of GLUT-4 to the plasma membrane and increased glucose uptake.

Ethanol impairs monosaccharide uptake and glycosylation in cultured rat astrocytes

“…Chronic alcohol intake also significantly increases GLUT1 in rat brain (Singh et al 1993). However, results regarding the effect of ethanol on other Glc transporters such as GLUT3 and GLUT4 (Krauss et al 1994;Yu et al 2000) suggest that the sensitivity to ethanol varies from one Glc transporter to another, depending on the cell type and ethanol doses. It has also been proposed that a sequence motif in GLUT1, absent in GLUT3 and GLUT4, confers ethanol sensitivity (Krauss et al 1994).…”

“…Asterisks indicate significant differences (Student's t-test, *p < 0.05). alcohol-induced increase uptake of this hexose in myotubes (Singh et al 1990(Singh et al , 1993(Singh et al , 1996Hu et al 1995;Nagamatzu et al 1995;Carver et al 1999;Yu et al 2000;Poirier et al 2001). These discrepancies may be due to marked differences in the experimental designs including ethanol doses, length of the treatments and the cell type or animal models used.…”

Hyperglycemia-Induced Apoptosis in Mouse Myocardium

“…The H9c2 cell line derived from embryonic rat hearts maintains some features of cardiac myocytes and has been used extensively in in vitro studies (45)(46)(47). In the present study, we selected the H9c2 cell line instead of neonatal cardiomyocytes as used in our previous studies (25)(26)(27)(28) for the following reasons: 1) the glucose transporting system in H9c2 cells has been investigated and does not differ from that in rat or mouse hearts (45,46); 2) as compared with neonatal cardiomyocyte culture, culturing of H9c2 cells is much easier and the phenotypes of the cultures are repeatable, but primary neonatal cardiomyocyte cultures are affected by individual differences among the litters of mice; however, additional study to understand the effect of hyperglycemia directly on myocardial cells in vivo is necessary.…”

“…In the present study, we selected the H9c2 cell line instead of neonatal cardiomyocytes as used in our previous studies (25)(26)(27)(28) for the following reasons: 1) the glucose transporting system in H9c2 cells has been investigated and does not differ from that in rat or mouse hearts (45,46); 2) as compared with neonatal cardiomyocyte culture, culturing of H9c2 cells is much easier and the phenotypes of the cultures are repeatable, but primary neonatal cardiomyocyte cultures are affected by individual differences among the litters of mice; however, additional study to understand the effect of hyperglycemia directly on myocardial cells in vivo is necessary. Nevertheless, the present study does provide evidence that hyperglycemia induces cardiac cell apoptosis in vivo, and ROS generation by high levels of glucose likely triggers the mitochondrial cytochrome c-mediated caspase-3 activation pathway.…”

Ethanol Alters Endosomal Recycling of Human Dopamine Transporters

“…DAT and other neurotransmitter transporters recycle in a constitutive manner. However, intrinsic and pharmacological modulators can also regulate endosomal recycling, mediating changes in neurotransmission (5,(35)(36)(37)(38)(39)(40)(41). Alterations in cell surface transporter expression arise from modulation of transporter insertion, internalization or both steps of the recycling pathway.…”