Summary: Influx of Ca into was measured under experimental conditions which enabled measurements of initial rate of transport across the plasma membrane, without interference by the vacuolar Ca transport system. Addition of glucose or glycerol to the cells, after pre-incubation in glucose-free medium for 5 min, caused a rapid, transient increase in Ca influx, reaching a peak at 3–5 min after addition of substrate. Ethanol, or glycerol added with antimycin A, had no effect on Ca influx. We have shown previously that this increase is not mediated by an effect of the substrates on intracellular ATP levels. Changes in membrane potential accounted for only a part of the glucose-stimulated Ca influx. The roles of intracellular acidification and changes in cellular cAMP in mediating the effects of glucose on Ca influx were examined. After a short preincubation in glucose-free medium addition of glucose caused a decrease in the intracellular pH, [pH], which reached a minimum value after 3 min. A transient increase in the cellular cAMP level was also observed. Addition of glycerol also caused intracellular acidification, but ethanol or glycerol added with antimycin A had no effect on [pH]. Artificial intracellular acidification induced by exposure to isobutyric acid or to CCCP caused a transient rise in Ca influx but the extent of the increase was smaller than that caused by glucose, and the time-course was different. We conclude that intracellular acidification may be responsible for part of the glucose stimulation of Ca influx. The role of the increase in cAMP level on Ca influx was examined by measuring the effect of glucose and of artificial intracellular acidification on Ca influx in a strain which lacks adenylate cyclase activity. In this strain, addition of glucose or isobutyric acid still led to a transient increase in Ca transport. Therefore, we concluded that at least part of the increase in Ca influx in response to glucose is cAMP-independent.


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