ATP-dependent acidification and tonoplast hyperpolarization in isolated vacuoles from green suspension cells of Chenopodium rubrum L.

The tonoplast of isolated vacuoles from photoautotrophic suspension cells of Chenopodium rubrum L. was studied by means of the patch-clamp technique. In a symmetrical K(+) concentration of 46 mM, similar to in vivo conditions, the tonoplast displayed a membrane potential near zero and a linear current-voltage relationship with a mean slope of 1.0 S/m(2). ATP at 2 mM hyperpolarized the tonoplast (vacuole positive) by 15-20 mV and, in a parallel experiment, acidified the vacuole (outside pH 7.0) to pH 5.0, as monitored by accumulation of acridine orange. Analysis of the voltage-clamp current indicates a 2-fold, ATP-dependent increase of the membrane capacitance, from 4 to 8 mF/m(2), and an ATP-independent, unidentified ion channel having a mean opening time of about 5 msec and a conductivity of 0.5-1.0 pS.