Microelectrode Measurements on Red Beet Vacuole : Biological Effect of Na OR NO(3) Ions, Diffusing from the Microelectrode.

Glass microelectrodes filled with 3 molar KCl are widely used to measure intracellular potentials and it is usual to try to minimize their electrolyte loss. In these experiments we have used the ionic leak of our microelectrodes, filled with various salt solutions, to introduce a given ion into the red beet vacuole. This allowed us to show that NO(3) (-) ions reduce the magnitude of the current spectral density while they do not change the resistance of the tonoplast. This is true when NO(3) (-) is either added to the external medium or used as the microelectrode filling solution. This can be interpreted by a NO(3) (-) effect on the vacuolar side of the tonoplast, resulting in an inhibition of the ion transporting ATPase. Replacing K(+) by Na(+) ions in the medium has no effect on tonoplast resistance (R(s)). On the contrary, when ions leaking from the microelectrode are H(+), Li(+) or K(+), R(s) is close to 4 kilohm square centimeter, whereas R(s) is of the order of 30KOmega square centimeter when Na(+) are the leaking ions. We also found a possible correlation between the presence of a Lorentzian in the current spectral density (cut-off frequency = 2 hertz) and a Cl(-) efflux from the vacuole. This could be explained by the existence of Cl(-) channels on the tonoplast.