Abstract
In voltage-clamp experiments, a two-pulse procedure was used to investigate the ionic currents underlying the action potential in Chara inflata. A prepulse hyperpolarized the membrane from a resting potential of about -100 to -200 mV. The prepulse was followed by a second pulse that changed the potential difference (p.d.) to -100 mV and less negative values in steps of 20 mV. This two-pulse procedure induces action potentials that have a reproducible time course, which is essential for any comparative investigation of the action potential. The two-pulse procedure reveals that in the charophyte C. inflata the electric current flowing across the cell membranes during positive voltage-clamp steps from the resting p.d. consists of a leak current flowing from the start of the pulse, followed by a transient inward-going current, Ii, commencing after a delay, and preceding a delayed transient outward current, Io. The characteristics of the current components and their response to various ion channel blockers and ionic treatments suggest that: (a) Ii, which is blocked by the external application of 9-anthracenecarboxylic acid, is carried by Cl- and (b) Io, which is blocked by the external application of the organic anions tetraethylammonium (TEA+) and nonyltriethylammonium, is carried mainly by K+. The magnitude and behavior of these K+ and Cl- currents could be modified by changes in the external concentration of CaCl2, LiCl, or NaCl but not sorbitol. Hence, it is concluded that NaCl-enhanced transient inward Cl- current, Ii, is due to ionic effects of NaCl rather than to its osmotic effects. The modification of the K+ current, Io, either by changing external K+ concentrations or by blocking the current with TEA+, also alters the Cl- currents Ii.
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Selected References
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- Bryant S. H., Morales-Aguilera A. Chloride conductance in normal and myotonic muscle fibres and the action of monocarboxylic aromatic acids. J Physiol. 1971 Dec;219(2):367–383. doi: 10.1113/jphysiol.1971.sp009667. [DOI] [PMC free article] [PubMed] [Google Scholar]
- GAFFEY C. T., MULLINS L. J. Ion fluxes during the action potential in Chara. J Physiol. 1958 Dec 30;144(3):505–524. doi: 10.1113/jphysiol.1958.sp006116. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Keifer D. W., Spanswick R. M. Correlation of Adenosine Triphosphate Levels in Chara corallina with the Activity of the Electrogenic Pump. Plant Physiol. 1979 Aug;64(2):165–168. doi: 10.1104/pp.64.2.165. [DOI] [PMC free article] [PubMed] [Google Scholar]
- MULLINS L. J. Efflux of chloride ions during the action potential of Nitella. Nature. 1962 Dec 8;196:986–987. doi: 10.1038/196986a0. [DOI] [PubMed] [Google Scholar]
- Okazaki Y., Tazawa M. Calcium ion and turgor regulation in plant cells. J Membr Biol. 1990 Apr;114(3):189–194. doi: 10.1007/BF01869213. [DOI] [PubMed] [Google Scholar]
- Spyropoulos C. S., Tasaki I., Hayward G. Fractionation of Tracer Effluxes during Action Potential. Science. 1961 Jun 30;133(3470):2064–2065. doi: 10.1126/science.133.3470.2064. [DOI] [PubMed] [Google Scholar]
- Williamson R. E., Ashley C. C. Free Ca2+ and cytoplasmic streaming in the alga Chara. Nature. 1982 Apr 15;296(5858):647–650. doi: 10.1038/296647a0. [DOI] [PubMed] [Google Scholar]