PHARMACOLOGY OF THE SV CHANNEL IN THE VACUOLAR MEMBRANE OF CHENOPODIUM-RUBRUM SUSPENSION CELLS

Single channel performance and deactivation currents have been analyze d in the presence of cation channel blockers to reveal pharmacological properties of the slow-activating (SV) cation-selective ion channel i n the vacuolar membrane (tonoplast) isolated from suspension cells of Chenopodium rubrum L. At a holding potential of - 100 mV, the SV chann el showed half-maximal inhibition with 20 mm tetraethylammonium (TEA), 7 mum 9-amino-acridine, 6 mum (+)-tubocurarine, 300 nm quinacrine, an d 35 mum quinine, respectively. The SV channel is also blocked by char ybdotoxin (20 nm at - 80 mV) but not by apamine. 9-Amino-acridine, (+) tubocurarine and quinacrine act in a voltage-dependent fashion, bindin g to the open channel and to different sites along the transmembrane v oltage profile according to Woodhull (J. Gen. Physiol. 61:687-708, 197 3). No binding site could be specified for charybdotoxin, which binds to the closed channel, and for quinine. Except for quinine, all tested blockers were effective only if added to the cytoplasmic side of the tonoplast. A structural relationship between the SV channel and Maxi-K channels in animal systems is inferred.