Abstract
The whole-cell configuration of the patch clamp technique was used to study both outward and inward ion currents across the plasma membrane of tobacco (Nicotiana tabacum) protoplasts from cell-suspension cultures. The ion currents across the plasma membrane were analyzed by the application of stepwise potential changes from a holding potential or voltage ramps. In all protoplasts, a voltage- and time-dependent outward rectifying current was present. The conductance increased upon depolarization of the membrane potential (to >0 mV) with a sigmoidal time course. The reversal potential of the outward current shifted in the direction of the K+ equilibrium potential upon changing the external K+ concentration. The outward current did not show inactivation. In addition to the outward rectifying current, in about 30% of the protoplasts, a time- and voltage-dependent inward rectifying current was present as well. The inward rectifying current activated upon hyperpolarization of the membrane potential (<-100 mV) with an exponential time course. The reversal potential of the inward conductance under different ionic conditions was close to the K+ equilibrium potential.
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Selected References
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- Briskin D. P., Leonard R. T. Ion Transport in Isolated Protoplasts from Tobacco Suspension Cells: III. Membrane Potential. Plant Physiol. 1979 Dec;64(6):959–962. doi: 10.1104/pp.64.6.959. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Dangl J. L., Hauffe K. D., Lipphardt S., Hahlbrock K., Scheel D. Parsley protoplasts retain differential responsiveness to u.v. light and fungal elicitor. EMBO J. 1987 Sep;6(9):2551–2556. doi: 10.1002/j.1460-2075.1987.tb02543.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fairley-Grenot K., Assmann S. M. Evidence for G-Protein Regulation of Inward K+ Channel Current in Guard Cells of Fava Bean. Plant Cell. 1991 Sep;3(9):1037–1044. doi: 10.1105/tpc.3.9.1037. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fairley K., Laver D., Walker N. A. Whole-cell and single-channel currents across the plasmalemma of corn shoot suspension cells. J Membr Biol. 1991 Apr;121(1):11–22. doi: 10.1007/BF01870647. [DOI] [PubMed] [Google Scholar]
- Hamill O. P., Marty A., Neher E., Sakmann B., Sigworth F. J. Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflugers Arch. 1981 Aug;391(2):85–100. doi: 10.1007/BF00656997. [DOI] [PubMed] [Google Scholar]
- Ketchum K. A., Shrier A., Poole R. J. Characterization of potassium-dependent currents in protoplasts of corn suspension cells. Plant Physiol. 1989 Apr;89(4):1184–1192. doi: 10.1104/pp.89.4.1184. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kourie J., Goldsmith M. H. K Channels Are Responsible for an Inwardly Rectifying Current in the Plasma Membrane of Mesophyll Protoplasts of Avena sativa. Plant Physiol. 1992 Mar;98(3):1087–1097. doi: 10.1104/pp.98.3.1087. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Moran N., Ehrenstein G., Iwasa K., Mischke C., Bare C., Satter R. L. Potassium Channels in Motor Cells of Samanea saman: A Patch-Clamp Study. Plant Physiol. 1988 Nov;88(3):643–648. doi: 10.1104/pp.88.3.643. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schroeder J. I., Fang H. H. Inward-rectifying K+ channels in guard cells provide a mechanism for low-affinity K+ uptake. Proc Natl Acad Sci U S A. 1991 Dec 15;88(24):11583–11587. doi: 10.1073/pnas.88.24.11583. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schroeder J. I. K+ transport properties of K+ channels in the plasma membrane of Vicia faba guard cells. J Gen Physiol. 1988 Nov;92(5):667–683. doi: 10.1085/jgp.92.5.667. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schroeder J. I. Quantitative analysis of outward rectifying K+ channel currents in guard cell protoplasts from Vicia faba. J Membr Biol. 1989 Mar;107(3):229–235. doi: 10.1007/BF01871938. [DOI] [PubMed] [Google Scholar]