The vacuolar Ca2+/H+ exchanger Vcx1p/Hum1p tightly controls cytosolic Ca2+levels in S-cerevisiae

It is well established that the vacuole plays an important role in the cell ular adaptation to growth in the presence of elevated extracellular Ca2+ co ncentrations in Saccharomyces cerevisiae. The Ca2+ ATPase Pmc1p and the Ca2 +/H+ exchanger Vcx1p/Hum1p have been shown to facilitate Ca2+ sequestration into the vacuole. However, the distinct physiological roles of these two v acuolar Ca2+ transporters remain uncertain. Here we show that Vcx1p can rap idly sequester a sudden pulse of cytosolic Ca2+ into the vacuole, while Pmc 1p carries out this function much less efficiently, This finding is consist ent with the postulated role of Vcx1p as a high capacity, low affinity Ca2 transporter and suggests that Vcx1p may act to attenuate the propagation o f Ca2+ signals in this organism. (C) 1999 Federation of European Biochemica l Societies.