Abstract
Fast activating vacuolar (FV) channels, which are permeable for small monovalent cations, dominate the ion conductance of the vacuolar membrane at physiological Ca2+ concentrations. Here the effect of Mg2+ on FV channels was studied. Patch-clamp measurements were performed on whole barley (Hordeum vulgare) mesophyll vacuoles and on excised tonoplast patches. Free Mg2+ concentrations in the millimolar range inhibited FV channels from the cytosolic and the vacuolar side. Increasing cytosolic free Mg2+ decreased the open probability of FV channels without affecting single channel current amplitudes. The Mg2+ effect showed a bell-shaped voltage-dependence and was most pronounced at voltages between −40 and −60 mV. The dose dependence of the FV channel inhibition by cytosolic Mg2+ could be described by a simple Michaelis-Menten type of binding with Kd values of 10 and 35 µM at −60 mV and +100 mV, respectively.
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