Figure 2

Native K⁺ and Cl^- currents in tobacco mesophyll protoplasts transformed by the empty pLoc vector. (A, B) Typical recordings illustrating the two patterns of whole-cell inward K⁺ currents elicited by membrane hyperpolarisation. 35 % of the patch-clamped protoplasts displayed the "no-current" pattern shown in (A). 65 % of the patch-clamped protoplasts displayed the voltage-dependent instantaneous weak current pattern shown in (B). (C) Typical recordings of whole-cell outward K⁺ currents elicited by membrane depolarisation on the same protoplasts as in (A) and (B). The voltage steps ranged from -60 mV to -200 mV (A, B) and from -40 mV to +100 mV (C) in +20 mV increments, from a holding potential of -40 mV. The symbol above the records in a-c indicates the time of "steady-state" current sampling. (D) Average (mean ± SE, n = 10) of native steady-state K⁺ currents in tobacco mesophyll protoplasts plotted against membrane potential. (E) Typical recordings of native whole-cell Cl^- currents recorded in protoplasts exposed to CsCl in pipette and extracellular solutions (see "Methods"). The voltage steps ranged from -202 mV to +58 mV in +20 mV increments and the holding potential was -22 mV. Dashed line marks zero current level. The symbol above the records indicates the time of "steady-state" current sampling. (F) Average (mean ± SE, n = 10) of native steady-state Cl^-currents in tobacco mesophyll protoplasts plotted against membrane potential. Voltage dependence, at steady state, of the native chloride currents in tobacco mesophyll protoplasts (means ± SE; n = 10). E_Cl, E_Cs and E_Ca represent equilibrium potentials for Cl^-, Cs⁺ and Ca²⁺ respectively (see detailed content of bath and pipette solutions in "Methods").