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Interconversion of Fast and Slow Gating Modes of Gcac1, a Guard-Cell Anion Channel
Planta, 195 (2): 301-304 (1994)Py377 Times Cited:36 Cited References Count:16.
Аннотация
For guard-cell protoplasts of Vicia faba L. we elucidated whether the slow (S-type) and rapid (R-type) activating anion channels represent different gating modes of GCAC1, the Guard Cell Anion Channel. in the whole-cell configuration of the patch-clamp technique, GCAC1 was activated in a Ca2+- and nucleotide-dependent manner. Cell-free outside-out membrane patches were isolated to determine the relative contribution of different gating modes or channel types to the overall anion current in this cell type. Within 2-15 min after the loss of cytoplasmic control through patch excision, depolarization-activated 38-pS channels characterized by flickering openings in the millisecond range convert into a channel of similar conductance but prolonged open times (hundreds of milliseconds) and lack of pronounced voltage-dependence. The rapid (R-type) and slow (S-type) gating modes exhibited similar ion selectivity but different susceptibility towards block by the stilbene derivative DNDS (4,4'-dinitrostilbene-2,2'-disulfonic acid). On R-type channels DNDS caused a flickering block and a shift in the threshold potential of activation whereas S-type channels remained unaffected. Because of the striking similarities of both channels with respect to single-channel conductance and relative permeability sequence on the one hand, but time-dependent conversion of R- into S-type gating after patch-excision on the other, we conclude that the mode of action of GCAC1 is under the control of cytoplasmic factors.
