Ethanol induces calcium influx via the Cch1-Mid1 transporter in <Emphasis Type="Italic">Saccharomyces</Emphasis><Emphasis Type="Italic">cerevisiae</Emphasis>

Yeast suffers from a variety of environmental stresses, such as osmotic pressure and ethanol produced during fermentation. Since calcium ions are protective for high concentrations of ethanol, we investigated whether Ca²⁺ flux occurs in response to ethanol stress. We find that exposure of yeast to ethanol induces a rise in the cytoplasmic concentration of Ca²⁺. The response is enhanced in cells shifted to high-osmotic media containing proline, galactose, sorbitol, or mannitol. Suspension of cells in proline and galactose-containing media increases the Ca²⁺ levels in the cytoplasm independent of ethanol exposure. The enhanced ability for ethanol to induce Ca²⁺ flux after the hypertonic shift is transient, decreasing rapidly over a period of seconds to minutes. There is partial recovery of the response after zymolyase treatment, suggesting that cell wall integrity affects the ethanol-induced Ca²⁺ flux. Acetate inhibits the Ca²⁺ accumulation elicited by the ethanol/osmotic stress. The Ca²⁺ flux is primarily via the Cch1 Ca²⁺ influx channel because strains carrying deletions of the cch1 and mid1 genes show greater than 90% reduction in Ca²⁺ flux. Furthermore, a functional Cch1 channel reduced growth inhibition by ethanol.