Transient increase in Ca2+ influx in Saccharomyces cerevisiae in response to glucose: effects of intracellular acidification and cAMP levels.
Influx of 45Ca2+ into Saccharomyces cerevisiae was measured under experimental conditions which enabled measurements of initial rate of transport across the plasma membrane, without interference by the vacuolar Ca2+ 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 45Ca2+ influx, reaching a peak at 3-5 min after addition of substrate. Ethanol, or glycerol added with antimycin A, had no effect on 45Ca2+ 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 45Ca2+ influx. The roles of intracellular acidification and changes in cellular cAMP in mediating the effects of glucose on 45Ca2+ influx were examined. After a short preincubation in glucose-free medium addition of glucose caused a decrease in the intracellular pH, [pH]i, 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]i. Artificial intracellular acidification induced by exposure to isobutyric acid or to CCCP caused a transient rise in Ca2+ 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 Ca2+ influx.(ABSTRACT TRUNCATED AT 250 WORDS)
Eilam
Y
Y
Department of Bacteriology, Hebrew University, Hadassah Medical School, Jerusalem, Israel.
Othman
M
M
Halachmi
D
D
D000968:Antimycin A / Q000494:pharmacology; D001693:Biological Transport, Active; D002087:Butyrates / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D000431:Ethanol / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D005990:Glycerol / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D058610:Isobutyrates; D007700:Kinetics; D008564:Membrane Potentials; D012441:Saccharomyces cerevisiae / Q000378:metabolism*
D002087:Butyrates; D058610:Isobutyrates; D000431:Ethanol; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000968:Antimycin A; C020380:isobutyric acid; D000242:Cyclic AMP; D005947:Glucose; D005990:Glycerol; D002118:Calcium