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Activation of Ca2+influx by metabolic substrates in Saccharomyces cerevisiae: role of membrane potential and cellular ATP levels
Abstract
Influx of Ca2+into cells of Saccharomyces cerevisiae was measured under non-steady-state conditions, which enable measurements of the initial rate of transport across plasma membranes without interference by the vacuolar Ca2+transport system. Removal of glucose from the incubation medium led to inactivation of Ca2+influx within 5 min. Readdition of glucose led to a transient increase in the rate of Ca2+transport, reaching a peak after 3–5 min. A second increase was observed 60–80 min later. To examine whether the first transient activation of Ca2+influx by glucose was mediated by membrane hyperpolarization, influx of 45Ca2+was measured in the presence and absence of metabolic substrates (glucose, glycerol, and glucose plus antimycin A) in cells hyperpolarized to different values of membrane potential (∆ψ). Logarithms of the rate of Ca2+influx were plotted against values of ∆ψ. Two different slopes were obtained, depending upon whether the metabolic substrate was present or absent. Ca2+influx in the presence of the metabolic substrates was always higher than expected by their effect on ∆ψ. Glycerol plus antimycin A did not affect Ca2+influx. It was concluded that metabolized substrates activate Ca2+influx not only by effects on ∆ψ but also by additional mechanism(s). Since no simple correlation between Ca2+influx and intracellular ATP levels was observed, it was concluded that ATP levels do not affect the initial rates of Ca2+transport across the plasma membrane of S. cerevisiae.
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© Society for General Microbiology, 1990