Detailed patch-clamp studies have been made of ion channels in the plasma membrane and tonoplast of the yeast Saccharomyces cerevisiae. The predominant tonoplast channel is a high-conductance cation-selective inward rectifier (passing ions easily into the cytoplasm from the vacuole), with its open probability (Po) peaking at about -80 mV (cytoplasm negative) and falling to near zero at +80 mV. It has a maximal slope conductance of approximately 150 pS in 100 mmol l-1 KCl, and conducts Na+, K+ and Ca2+. Elevated cytoplasmic Ca2+ concentration, alkaline pH and reducing agents can activate the channel, its likely physiological function being to adjust cytoplasmic Ca2+ concentration from the vacuolar reservoir. The predominant plasma-membrane channel is a strongly outward rectifying K+ channel (passing K+ easily out of the cytoplasm to the extracellular medium), which is activated by positive-going membrane voltages as well as by elevated cytoplasmic Ca2+ concentration and alkaline pH. Interaction between membrane voltage and [Ca2+]cyt is complex and defines three parallel closed states for the channel: a Ca(2+)-independent brief closure (I), a calcium-inhibited long closure (G) and, at large positive voltages, a calcium-induced brief blockade (B). This channel is likely to function in steady-state turgor regulation and in charge balancing during proton-coupled substrate uptake.
Complex modulation of cation channels in the tonoplast and plasma membrane of Saccharomyces cerevisiae: single-channel studies.
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A Bertl, C L Slayman; Complex modulation of cation channels in the tonoplast and plasma membrane of Saccharomyces cerevisiae: single-channel studies.. J Exp Biol 1 November 1992; 172 (1): 271–287. doi: https://doi.org/10.1242/jeb.172.1.271
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