THE CHAOTROPIC ANIONS THIOCYANATE AND NITRATE INHIBIT THE ELECTRIC-CURRENT THROUGH THE TONOPLAST ATPASE OF ISOLATED VACUOLES FROM SUSPENSION CELLS OF CHENOPODIUM-RUBRUM

Using the whole-vacuolar mode of the patch clamp technique, we studied the effect of the chaotropic anions thiocyanate and nitrate on the el ectric currents generated by the proton pumping tonoplast ATPase and p yrophosphatase (PP(i)ase), respectively, in vacuoles from suspension c ells of Chenopodium rubrum L. Addition of KNO3 (150-250 mM) or KSCN (7 0-150 mM), and ATP (5 mM, obligatory) irreversibly inhibited the subse quent electric current through the tonoplast ATPase driven by 1 mM ATP , whereas PPiase-activity by 50 mu M PPi remained unaffected. The kine tics of inhibition, indicative of ATPase disintegration by the chaotro pic anions, follows a single exponential (tau = 3.44 min). However, ap parent ATPase disintegration did not measurably increase the tonoplast conductance. We conclude that, by contrast to organellar F-ATPases, u pon disintegration the transmembrane proteolipid of the V-ATPase does not act as a proton conductor which, in the presence of chaotropic ani ons, like chloride or nitrate, would severely perturb solute compartme ntation in the plant cell.