Abstract
A number of models proposed to account for the sodium conductance changes are shown to fall into two classes. The Hodgkin-Huxley (HH) model falls into a class (I) in which the conductance depends on two or more independent variables controlled by independent processes. The Mullins, Hoyt, and Goldman models fall into class II in which conductance depends directly on one variable only, a variable which is controlled by two or more coupled processes. The HH and Hoyt models are used as specific examples of the two classes. It is shown that, contrary to a recently published report, the results from double experiments can be equally well accounted for by both models. It is also shown that steady-state conditioning, or “inactivation,” curves, obtained at more than one test potential, can be used to distinguish the two models. The HH equations predict that such curves should be shifted, by very small amounts, in the hyperpolarizing direction when more depolarizing test potentials are used, while the Hoyt model predicts that they should be shifted in the depolarizing direction, by quite appreciable amounts. Several pieces of published experimental information are used as tests of these predictions, and give tentative support to the class II model. Further experiments are necessary before a definite conclusion can be reached.
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Selected References
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- ADELMAN W. J., Jr, FOK Y. B. INTERNALLY PERFUSED SQUID AXONS STUDIED UNDER VOLTAGE CLAMP CONDITIONS. II. RESULTS. THE EFFECTS OF INTERNAL POTASSIUM AND SODIUM ON MEMBRANE ELECTRICAL CHARACTERISTICS. J Cell Physiol. 1964 Dec;64:429–443. doi: 10.1002/jcp.1030640315. [DOI] [PubMed] [Google Scholar]
- Adelman W. J., Jr, Senft J. P. Effects of internal sodium on ionic conductance of internally perfused axons. Nature. 1966 Nov 5;212(5062):614–616. doi: 10.1038/212614a0. [DOI] [PubMed] [Google Scholar]
- Chandler W. K., Hodgkin A. L., Meves H. The effect of changing the internal solution on sodium inactivation and related phenomena in giant axons. J Physiol. 1965 Oct;180(4):821–836. doi: 10.1113/jphysiol.1965.sp007733. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Chandler W. K., Meves H. Incomplete sodium inactivation in internally perfused giant axons from Loligo forbesi. J Physiol. 1966 Oct;186(2):121P–122P. [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]
- FRANKENHAEUSER B. Quantitative description of sodium currents in myelinated nerve fibres of Xenopus laevis. J Physiol. 1960 Jun;151:491–501. doi: 10.1113/jphysiol.1960.sp006455. [DOI] [PMC free article] [PubMed] [Google Scholar]
- FRANKENHAEUSER B. Steady state inactivation of sodium permeability in myelinated nerve fibres of Xenopus laevis. J Physiol. 1959 Oct;148:671–676. doi: 10.1113/jphysiol.1959.sp006316. [DOI] [PMC free article] [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]
- HOYT R. C. THE SQUID GIANT AXON. MATHEMATICAL MODELS. Biophys J. 1963 Sep;3:399–431. doi: 10.1016/s0006-3495(63)86829-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
- MULLINS L. J. An analysis of pore size in excitable membranes. J Gen Physiol. 1960 May;43:105–117. doi: 10.1085/jgp.43.5.105. [DOI] [PMC free article] [PubMed] [Google Scholar]
- NOBLE D. A modification of the Hodgkin--Huxley equations applicable to Purkinje fibre action and pace-maker potentials. J Physiol. 1962 Feb;160:317–352. doi: 10.1113/jphysiol.1962.sp006849. [DOI] [PMC free article] [PubMed] [Google Scholar]