Abstract
Isolated axons from the squid, Dosidicus gigas, were internally perfused with potassium fluoride solutions. Membrane currents were measured following step changes of membrane potential in a voltage-clamp arrangement with external isosmotic solution changes in the order: potassium-free artificial seawater; potassium chloride; potassium chloride containing 10, 25, 40 or 50, mM calcium or magnesium; and potassium-free artificial seawater. The following results suggest that the currents measured under voltage clamp with potassium outside and inside can be separated into two components and that one of them, the predominant one, is carried through the potassium system. (a) Outward currents in isosmotic potassium were strongly and reversibly reduced by tetraethylammonium chloride. (b) Without calcium or magnesium a progressive increase in the nontime-dependent component of the currents (leakage) occurred. (c) The restoration of calcium or magnesium within 15–30 min decreases this leakage. (d) With 50 mM divalent ions the steady-state current-voltage curve was nonlinear with negative resistance as observed in intact axons in isosmotic potassium. (e) The time-dependent components of the membrane currents were not clearly affected by calcium or magnesium. These results show a strong dependence of the leakage currents on external calcium or magnesium concentration but provide no support for the involvement of calcium or magnesium in the kinetics of the potassium system.
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Selected References
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- Armstrong C. M. Time course of TEA(+)-induced anomalous rectification in squid giant axons. J Gen Physiol. 1966 Nov;50(2):491–503. doi: 10.1085/jgp.50.2.491. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Chandler W. K., Meves H. Voltage clamp experiments on internally perfused giant axons. J Physiol. 1965 Oct;180(4):788–820. doi: 10.1113/jphysiol.1965.sp007732. [DOI] [PMC free article] [PubMed] [Google Scholar]
- DEFFNER G. G. The dialyzable free organic constituents of squid blood; a comparison with nerve axoplasm. Biochim Biophys Acta. 1961 Feb 18;47:378–388. doi: 10.1016/0006-3002(61)90298-0. [DOI] [PubMed] [Google Scholar]
- HODGKIN A. L., HUXLEY A. F. A quantitative description of membrane current and its application to conduction and excitation in nerve. J Physiol. 1952 Aug;117(4):500–544. doi: 10.1113/jphysiol.1952.sp004764. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lecar H., Ehrenstein G., Binstock L., Taylor R. E. Removal of potassium negative resistance in perfused squid giant axons. J Gen Physiol. 1967 Jul;50(6):1499–1515. doi: 10.1085/jgp.50.6.1499. [DOI] [PMC free article] [PubMed] [Google Scholar]
- MOORE J. W. Excitation of the squid axon membrane in isosmotic potassium chloride. Nature. 1959 Jan 24;183(4656):265–266. doi: 10.1038/183265b0. [DOI] [PubMed] [Google Scholar]
- SEGAL J. R. An anodal threshold phenomenon in the squid giant axon. Nature. 1958 Nov 15;182(4646):1370–1370. doi: 10.1038/1821370a0. [DOI] [PubMed] [Google Scholar]
- TAYLOR R. E., MOORE J. W., COLE K. S. Analysis of certain errors in squid axon voltage clamp measurements. Biophys J. 1960 Nov;1:161–202. doi: 10.1016/s0006-3495(60)86882-8. [DOI] [PMC free article] [PubMed] [Google Scholar]