Ethanol alters the expression of ion channel genes in Daphnia pulex

Background: Heavy drinking can increase heart rate and blood glucose, induce hypoxic tolerance, impair brain cognitive functions, and alter gene expressions. These phenomena may occur even in response to small dose of ethanol exposure or during its withdrawal. Objectives: To evaluate whether persistent low concentrations of ethanol exposure affect organism function and the gene expressions of ion channels. Methods: Daphnids were randomized to receive placebo 300 min, 2 mM ethanol 300 min, or 2 mM ethanol 240 min and then placebo 60 min. Heart rate, glucose levels, phototactic behavior, and hypoxic tolerance were recorded during experiment. At the end of the study, changes in the mRNA levels of ion channel genes were assessed in response to exposure to ethanol using quantitative polymerase chain reaction (PCR) techniques. Results: Heart rate was reversibly increased by ethanol withdrawal and returned to basal levels upon re-exposure to ethanol. Fifteen of 120 ion channel transcripts were affected by persistent ethanol exposure. Neither ethanol withdrawal nor persistent exposures showed an effect on blood glucose, phototactic behavior, or hypoxic tolerance. Conclusions: Small doses of ethanol can increase heart rate and alter gene expression of multiple ion channels in Daphnia pulex. Affected ion channel genes may assist in understanding the mechanism of ethanol adaptation and tolerance.