Properties of Single K + and Cl − Channels in Asclepias tuberosa Protoplasts

Abstract

Potassium and chloride channels were characterized in Asckpias tub-erosa suspension cell derived protoplasts by patch voltage-clamp. Whole-cell currents and single channels in excised patches had linear instantaneous current-voltage relations, reversing at the Nernst potentials for K' and C17, respectively. Whole cell K' currents activated exponentially during step depolarizations, while voltage-dependent Cl-channels were activated by hyperpolarizations. Single K' channel conductance was 40 ± 5 pS with a mean open time of 4.5 millisecondsat 100 millivolts. Potassium channels were blocked by Cs' and tetraethylammonium, but were insensitive to 4-aminopyridine. Chloride channels had a single-channel conductance of 100 ± 17 picosiemens, mean open time of 8.8 milliseconds, and were blocked by Zn2" and ethacrynic acid. Whole-cell C-currents were inhibited by abscisic acid, and were unaffected by indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid. Since internal and external composition can be controlled, patch-clamped protoplasts are ideal systems for studying the role of ion channels in plant physiology and development.