A membrane-delimited pathway of G-protein regulation of the guard-cell inward K+ channel.
GTP-binding protein (G-protein) regulation of inward rectifying K+ channels in the plasma membrane of Vicia (Vicia faba L.) guard cells has previously been demonstrated at the whole-cell level. However, whether a cytosolic signal transduction chain is required for G-protein regulation of K+ channels in Vicia guard cells, or in any plant cell type, remains unknown. In the present study, we assayed effects of several G-protein regulators on inward K+ channels in isolated inside-out membrane patches from Vicia guard cell protoplasts. Guanosine 5'-[gamma-thio]triphosphate, a nonhydrolyzable GTP analog that locks G proteins into their activated state, decreased the open state probability (Po) of single inward K+ channels. This decrease in Po was accompanied by an increase in one of the closed time constants of the K+ channel. Guanosine 5'-[beta-thio]diphosphate, a GDP analog that locks G proteins into their inactivated state, slightly increased the Po of the inward K+ channel and shortened the closed time constants. Pertussis toxin and cholera toxin, which ADP-ribosylate G proteins at different sites, decreased the Po of the inward K+ channel. Our data indicate that G proteins can act via a membrane-delimited pathway to regulate inward K+ channels in the guard-cell plasma membrane.
Wu
W H
WH
Biological Laboratories, Harvard University, Cambridge, MA 02138.
Assmann
S M
SM
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D002772:Cholera Toxin / Q000494:pharmacology; D007887:Fabaceae / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D037342:Pertussis Toxin; D010946:Plants, Medicinal; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011336:Probability; D011523:Protoplasts / Q000502:physiology; D015398:Signal Transduction; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015221:Potassium Channels; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; C022571:adenosine 5'-O-(3-thiotriphosphate); D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D000255:Adenosine Triphosphate; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins