Abstract

Acute ethanol treatment of NG108-15 neuroblastoma x glioma hybrid cells results in inhibition of adenosine uptake with consequent increases in extracellular adenosine and intracellular cAMP concentrations. Chronic exposure to ethanol, however, causes heterologous desensitization of receptors coupled to adenylyl cyclase via stimulatory guanine nucleotide regulatory protein. This heterologous desensitization is correlated with a decrease in the amount of protein and mRNA for the GTP-binding subunit of stimulatory guanine nucleotide regulatory protein. In addition, after chronic exposure to ethanol, the adenosine transporter becomes tolerant to acute ethanol inhibition of adenosine uptake, and there is no longer an increase in extracellular adenosine. We have previously shown that extracellular adenosine is required for the development of ethanol-induced heterologous desensitization. To examine the role of adenosine receptors in mediating these responses to ethanol, we used BW A1434U, an adenosine receptor antagonist that does not inhibit nucleoside transport. BW A1434U caused a concentration-dependent inhibition of (-)-N6-(R-phenyl-isopropyl)-adenosine-stimulated cAMP production in NG108-15 cells. BW A1434U also completely blocked acute ethanol-induced increases in intracellular cAMP levels and prevented the development of ethanol-induced heterologous desensitization and the reduction in the GTP-binding subunit of stimulatory guanine nucleotide regulatory protein. In addition, BW A1434U prevented the development of tolerance to ethanol-induced inhibition of adenosine transport. Our results indicate that in NG108-15 cells, adenosine receptors mediate ethanol-induced changed in cAMP signal transduction and adenosine transport and that an adenosine receptor antagonist can block both these acute and chronic affects of ethanol.