Cytoplasmic magnesium regulates the fast activating vacuolar cation channel

J. Exp. Bot. 50 (339): 1547-1552 (1999)

Brüggemann, L.I., Pottosin, I.I. and Schönknecht, G.

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 K_d values of 10 and 35 µM at -60 mV and +100 mV, respectively.