ACTIVATION OF DIVALENT-CATION INFLUX INTO SACCHAROMYCES-CEREVISIAE CELLS BY HYPOTONIC DOWNSHIFT

Subjecting Saccharomyces cerevisiae cells to a hypotonic downshift by transferring cells from YPD medium containing 0.8 M sorbitol to YPD me dium without sorbitol induces a transient rapid influx of Ca2+ and oth er divalent cations into the cell. For cells grown in YPD at 37 degree s C, this hypotonic downshift increases Ca2+ accumulation 6.7-fold. Hy potonic downshift-induced Ca2+ accumulation and steady-state Ca2+ accu mulation in isotonic YPD medium are differentially affected by dodecyl amine and Mg2+. The Ca2+-influx pathway responsible for hypotonic-indu ced Ca2+ influx may account for about 10-35% of Ca2+ accumulation by c ells growing in YPD. Ca2+ influx is not required for cells to survive a hypotonic downshift. Hypotonic downshift greatly reduces the ability of S. cerevisiae cells to survive a 5-min exposure to 10 mM Cd2+ sugg esting that mutants resistant to acute Cd2+ exposure may help identify genes required for hypotonic downshift-induced divalent cation influx .