Abstract
A model of a 100 micrometers diameter Purkinje fiber with intercellular clefts was studied under voltage clamp conditions to examine the consequences of radial nonuniformity. Sodium and potassium conductances were distributed so that the surface and cleft membranes had similar channel density. Assuming that the model is appropriate, sodium current (and conductance) measured in the voltage clamp is grossly underestimated because of loss of voltage control of the cleft membrane. Under these conditions a value for g Na of about 15-20 mmho/cm2 of actual membrane is consistent with the experimental measurements of Dudel and Rüdel (1970. Pfluegers Arch. Eur. J. Physiol. 315:136-158.). Intermediate and slow currents (slow inward current and potassium current) appear to be accurately measured under the model conditions, despite some voltage nonuniformity within the cleft. This result depended on the presence of a residual sodium current, and experimental removal of sodium may alter this result. All effects of nonuniformity would be accentuated in fibers of larger diameter.
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Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Adrian R. H., Chandler W. K., Hodgkin A. L. The kinetics of mechanical activation in frog muscle. J Physiol. 1969 Sep;204(1):207–230. doi: 10.1113/jphysiol.1969.sp008909. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Baumgarten C. M., Isenberg G. Depletion and accumulation of potassium in the extracellular clefts of cardiac Purkinje fibers during voltage clamp hyperpolarization and depolarization. Pflugers Arch. 1977 Mar 11;368(1-2):19–31. doi: 10.1007/BF01063450. [DOI] [PubMed] [Google Scholar]
- Baumgarten C. M., Isenberg G., McDonald T. F., Ten Eick R. E. Depletion and accumulation of potassium in the extracellular clefts of cardiac Purkinje fibers during voltage clamp hyperpolarization and depolarization: experiments in sodium-free bathing media. J Gen Physiol. 1977 Aug;70(2):149–169. doi: 10.1085/jgp.70.2.149. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Dudel J., Rüdel R. Voltage and time dependence of excitatory sodium current in cooled sheep Purkinje fibres. Pflugers Arch. 1970;315(2):136–158. doi: 10.1007/BF00586657. [DOI] [PubMed] [Google Scholar]
- Délèze J. The recovery of resting potential and input resistance in sheep heart injured by knife or laser. J Physiol. 1970 Jul;208(3):547–562. doi: 10.1113/jphysiol.1970.sp009136. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fozzard H. A., Beeler G. W., Jr The voltage clamp and cardiac electrophysiology. Circ Res. 1975 Oct;37(4):403–413. doi: 10.1161/01.res.37.4.403. [DOI] [PubMed] [Google Scholar]
- Fozzard H. A. Membrane capacity of the cardiac Purkinje fibre. J Physiol. 1966 Jan;182(2):255–267. doi: 10.1113/jphysiol.1966.sp007823. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gilai A. Electromechanical coupling in tubular muscle fibers. II. Resistance and capacitance of one transverse tubule. J Gen Physiol. 1976 Mar;67(3):343–367. doi: 10.1085/jgp.67.3.343. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hellam D. C., Studt J. W. A core-conductor model of the cardiac Purkinje fibre based on structural analysis. J Physiol. 1974 Dec;243(3):637–660. doi: 10.1113/jphysiol.1974.sp010770. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hellam D. C., Studt J. W. Linear analysis of membrane conductance and capacitance in cardiac Purkinje fibres. J Physiol. 1974 Dec;243(3):661–694. doi: 10.1113/jphysiol.1974.sp010771. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lederer W. J., Tsien R. W. Transient inward current underlying arrhythmogenic effects of cardiotonic steroids in Purkinje fibres. J Physiol. 1976 Dec;263(2):73–100. doi: 10.1113/jphysiol.1976.sp011622. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mathias R. T., Eisenberg R. S., Valdiosera R. Electrical properties of frog skeletal muscle fibers interpreted with a mesh model of the tubular system. Biophys J. 1977 Jan;17(1):57–93. doi: 10.1016/S0006-3495(77)85627-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
- McAllister R. E., Noble D. The time and voltage dependence of the slow outward current in cardiac Purkinje fibres. J Physiol. 1966 Oct;186(3):632–662. doi: 10.1113/jphysiol.1966.sp008060. [DOI] [PMC free article] [PubMed] [Google Scholar]
- McAllister R. E., Noble D., Tsien R. W. Reconstruction of the electrical activity of cardiac Purkinje fibres. J Physiol. 1975 Sep;251(1):1–59. doi: 10.1113/jphysiol.1975.sp011080. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mobley B. A., Eisenberg B. R. Sizes of components in frog skeletal muscle measured by methods of stereology. J Gen Physiol. 1975 Jul;66(1):31–45. doi: 10.1085/jgp.66.1.31. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mobley B. A., Page E. The surface area of sheep cardiac Purkinje fibres. J Physiol. 1972 Feb;220(3):547–563. doi: 10.1113/jphysiol.1972.sp009722. [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]
- Reuter H., Scholz H. A study of the ion selectivity and the kinetic properties of the calcium dependent slow inward current in mammalian cardiac muscle. J Physiol. 1977 Jan;264(1):17–47. doi: 10.1113/jphysiol.1977.sp011656. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Reuter H. The dependence of slow inward current in Purkinje fibres on the extracellular calcium-concentration. J Physiol. 1967 Sep;192(2):479–492. doi: 10.1113/jphysiol.1967.sp008310. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schoenberg M., Dominguez G., Fozzard H. A. Effect of diameter on membrane capacity and conductance of sheep cardiac Purkinje fibers. J Gen Physiol. 1975 Apr;65(4):441–458. doi: 10.1085/jgp.65.4.441. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sommer J. R., Johnson E. A. Cardiac muscle. A comparative study of Purkinje fibers and ventricular fibers. J Cell Biol. 1968 Mar;36(3):497–526. doi: 10.1083/jcb.36.3.497. [DOI] [PMC free article] [PubMed] [Google Scholar]
- TASAKI I., HAGIWARA S. Capacity of muscle fiber membrane. Am J Physiol. 1957 Mar;188(3):423–429. doi: 10.1152/ajplegacy.1957.188.3.423. [DOI] [PubMed] [Google Scholar]
- WEIDMANN S. The electrical constants of Purkinje fibres. J Physiol. 1952 Nov;118(3):348–360. doi: 10.1113/jphysiol.1952.sp004799. [DOI] [PMC free article] [PubMed] [Google Scholar]