Characterization of a G-protein-regulated outward K+ current in mesophyll cells of vicia faba L.
Whole-cell voltage-dependent currents in isolated mesophyll protoplasts of Vicia faba were investigated by patch-clamp techniques. With 104 mM K+ in the cytosol and 13 mM K+ in the external solution, depolarization of the plasma membrane from -47 mV to potentials between -15 and +85 mV activated a voltage- and time-dependent outward current (Iout). The average magnitude of Iout at +85 mV was 28.5 +/- 3.3 pA.pF-1. No inward voltage-dependent current was observed upon hyperpolarization of the plasma membrane from -55 mV to potentials as negative as -175 mV. Time-activated outward current was blocked by Ba2+ (1 mM BaCl2) and was not observed when K+ was eliminated from the external and internal solutions, indicating that this outward current was carried primarily by K+ ions. The voltage dependency of outward K+ current revealed a possible mechanism for K+ efflux from mesophyll cells. A GDP analogue guanosine 5'-[beta-thio]diphosphate (500 microM) significantly enhanced outward K+ current. The outward K+ current was inhibited by the GTP analogue guanosine 5'-[gamma-thio]triphosphate (500 microM) and by an increase in cytoplasmic free Ca2+ concentrations. Cholera toxin, which ADP-ribosylates guanine nucleotide-binding regulatory proteins, also inhibited outward K+ current. These findings illustrate the presence in mesophyll cells of outward-rectifying K+ channels that are regulated by GTP-binding proteins and calcium.
Li
W
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Biological Laboratories, Harvard University, Cambridge, MA 02138.
Assmann
S M
SM
D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D002772:Cholera Toxin / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D037342:Pertussis Toxin; D059828:Plant Cells; D018521:Plant Physiological Phenomena; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011523:Protoplasts / Q000502:physiology; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015221:Potassium Channels; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; C030812:adenosine 5'-O-(2-thiodiphosphate); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D000244:Adenosine Diphosphate; C023427:guanosine 5'-O-(2-thiodiphosphate); D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid