Jg. Barbara et al., HYPERPOLARIZATION-ACTIVATED INWARD CHLORIDE CURRENT IN PROTOPLASTS FROM SUSPENSION-CULTURED CARROT CELLS, Protoplasma, 180(3-4), 1994, pp. 136-144
Plasmalemmal ionic currents from enzymatically-isolated protoplasts of
suspension-cultured carrot cells were investigated by patch-clamp tec
hniques. Among other currents, a novel hyperpolarization-activated, in
wardly-rectifying, whole-cell current was observed. The activation of
this current was fast in onset, and for large hyperpolarizations a cha
racteristic, rapid voltage-dependent inactivation was seen. Ion substi
tution 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 patch
es, inward single-channel chloride currents having an elementary condu
ctance of ca. 100 pS were observed. The open probability increased wit
h hyperpolarization. Similar single-channel currents were activated by
slight negative pressure applied to the pipette. These chloride curre
nts could contribute both to the control of membrane potential and in
the regulation of osmotic balance in carrot cells.