HODGKIN-HUXLEY ANALYSIS OF A GCAC1 ANION CHANNEL IN THE PLASMA-MEMBRANE OF GUARD-CELLS

A quantitative analysis of the time- and voltage-dependent kinetics of the guard cell anion channel (GCAC1) current in guard cell protoplast s from Vicia faba was analyzed using the whole-cell patch clamp techni que. The voltage-dependent steady-state activation of GCAC1 current fo llowed a Boltzmann distribution. For the corresponding steady-state va lue of the activation variable a power of two was derived which yielde d suitable fits of the time course of voltage-dependent current activa tion. The GCAC1 mediated chloride current could successfully be descri bed in terms of the Hodgkin-Huxley equations commonly evoked for the N a channel in nerve. After step depolarizations from a potential in the range of the resting potential to potentials above the equilibrium po tential for chloride an activation and also an inactivation could be d escribed. The gating of both processes exhibited an inverse relationsh ip on the polarity of the applied step potentials in the order of mill iseconds. Deactivating tail currents decline exponentially. The presen ted analysis contributes to the understanding of the rising phase of t he observed action potentials in guard cells of V. faba. Evidence is p resented that the voltage-dependent kinetic properties of the GCAC1 cu rrent are different from those properties described for the excitable anion currents in the plasmalemma of Chara corallina (Beilby & Coster, 1979a).