HYPERPOLARIZATION-ACTIVATED INWARD CHLORIDE CURRENT IN PROTOPLASTS FROM SUSPENSION-CULTURED CARROT CELLS

Plasmalemmal ionic currents from enzymatically-isolated protoplasts of suspension-cultured carrot cells were investigated by patch-clamp techniques. Among other currents, a novel hyperpolarization-activated, inwardly-rectifying, whole-cell current was observed. The activation of this current was fast in onset, and for large hyperpolarizations a characteristic, rapid voltage-dependent inactivation was seen. Ion substitution experiments indicate that this inward current was due mainly to efflux of chloride ions. No dependence on either internal or external calcium was found, and internal MgATP was not necessary. Surprisingly, zinc did not block this current. In hyperpolarized outside-out patches, inward single-channel chloride currents having an elementary conductance of ca. 100 pS were observed. The open probability increased with hyperpolarization. Similar single-channel currents were activated by slight negative pressure applied to the pipette. These chloride currents could contribute both to the control of membrane potential and in the regulation of osmotic balance in carrot cells.