Dual effect of monovalent cations on the glucose-induced transient increase in the rate of DMP influx into Saccharomyces cerevisiae.

The transient increase in the rate of 2-(4-di-methyl-aminostyryl)-1-ethylpyridinium (DMP) influx in Saccharomyces cerevisiae caused by addition of glucose to a suspension of non-metabolizing cells at relatively high pH can be prevented by monovalent cations. Their concentrations for half-maximum inhibition of DMP uptake are of the same order of magnitude as the corresponding Km values for their uptake into yeast cells. It is argued that the inhibition of DMP uptake by monovalent cations is caused by a fast depolarization of the cell membrane and a second further decrease in the rate of DMP uptake. The latter effect develops slowly with time and depends upon the extent of accumulation of the monovalent cations in the cells.