QUANTITATIVE-ANALYSIS OF SINGLE K+ CHANNELS IN THE TONOPLAST OF CHARA-CORALLINA - SELECTIVITY AND TEA BLOCKADE

Patch-clamp measurements were made on the tonoplast surrounding protoplasmic droplets using the inside-out configuration. Three channels with different unitary conductance were observed in symmetrical 150 mM KCl. Two of them are highly selective to K+ and have an unitary conductance of 132 and 89 pS. The selectivity sequence of the 132 pS K+ channel for monovalent cations was: K > Cs > Rb > Na. The mechanism of TEA blockade was investigated on both sides of the 132 pS K+ channel. Our results suggest the presence of two different binding sites for TEA in the channel. This block was voltage-dependent when TEA was added to the bath but not when it was added to the pipette.