Characterization of a G-protein-regulated outward K+ current in mesophyll cells of Vicia faba L.

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Abstract

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′-[β-thio]diphosphate (500 μM) significantly enhanced out-ward K+ current. The outward K+ current was inhibited by the GTP analogue guanosine 5′-[γ-thio]triphosphate (500 μM) 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.

Original languageEnglish (US)
Pages (from-to)262-266
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume90
Issue number1
DOIs
StatePublished - Jan 1 1993

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Mesophyll Cells
Vicia faba
Guanosine
GTP-Binding Proteins
Cell Membrane
Protoplasts
Diphosphates
Cholera Toxin
Patch-Clamp Techniques
Guanosine Triphosphate
Cytosol
Adenosine Diphosphate
Carrier Proteins
Ions
Calcium
barium chloride
triphosphoric acid

All Science Journal Classification (ASJC) codes

  • General

Cite this

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title = "Characterization of a G-protein-regulated outward K+ current in mesophyll cells of Vicia faba L.",
abstract = "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′-[β-thio]diphosphate (500 μM) significantly enhanced out-ward K+ current. The outward K+ current was inhibited by the GTP analogue guanosine 5′-[γ-thio]triphosphate (500 μM) 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.",
author = "Weiwei Li and Assmann, {Sarah Mary}",
year = "1993",
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T1 - Characterization of a G-protein-regulated outward K+ current in mesophyll cells of Vicia faba L.

AU - Li, Weiwei

AU - Assmann, Sarah Mary

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N2 - 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′-[β-thio]diphosphate (500 μM) significantly enhanced out-ward K+ current. The outward K+ current was inhibited by the GTP analogue guanosine 5′-[γ-thio]triphosphate (500 μM) 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.

AB - 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′-[β-thio]diphosphate (500 μM) significantly enhanced out-ward K+ current. The outward K+ current was inhibited by the GTP analogue guanosine 5′-[γ-thio]triphosphate (500 μM) 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.

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