Skip to main content
PMC home page
The Journal of General Physiology logoLink to The Journal of General Physiology
. 1977 May 1;69(5):517–536. doi: 10.1085/jgp.69.5.517

The resistance of the septum of the medium giant axon of the earthworm

P Brink, L Barr
PMCID: PMC2215082  PMID: 864430

Abstract

It is generally thought that nexuses constitute low-resistance pathways between cell interiors in epithelial, neural, muscular, and even connective tissues. However, there are no reliable estimates of the specific resistance of a nexus. The reason for this is that in most cases the surfaces of nexuses between cells are geometrically complex and therefore it has been very hard to accurately estimate nexal areas. However, the septa of the median giant axon have a relatively simple shape. Moreover, in this preparation, it is possible to make a measuring current flow parallel to the axon axis so that from the voltage difference appearing between intracellular electrodes during current flow, the specific septal membrane resistance could be calculated. The average specific nexal resistance obtained was 5.9 ω cm(2) if one assumes that 100 percent of the septum is nexus. The steady state I-V curve for the septum is linear (+/- 10 mV). Placement of electrodes was validated by septa even though the septa were found to be permeable to fluorescein and TEA. Exposure of the axon to hypertonic saline impedes the movement of fluorescein across the septa. By analogy with other tissues it is concluded that hypertonic solutions disrupt nexuses.

A mathematical model was derived which predicts the steady- state transmembrane potential vs. distance from a point source of intracellular current. When the specific nexal membrane resistance is 5.9 ω cm(2), the prediction closely approximates the fall of transmembrane potential vs. distance in an ordinary infinite cable. This is commensurate with the electrophysiological behavior of this multicellular “axon.”

Full Text

The Full Text of this article is available as a PDF (1.1 MB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. BARR L., DEWEY M. M., BERGER W. PROPAGATION OF ACTION POTENTIALS AND THE STRUCTURE OF THE NEXUS IN CARDIAC MUSCLE. J Gen Physiol. 1965 May;48:797–823. doi: 10.1085/jgp.48.5.797. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Barr L., Berger W., Dewey M. M. Electrical transmission at the nexus between smooth muscle cells. J Gen Physiol. 1968 Mar;51(3):347–368. doi: 10.1085/jgp.51.3.347. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Coggeshall R. E. A fine structural analysis of the ventral nerve cord and associated sheath of Lumbricus terrestris L. J Comp Neurol. 1965 Dec;125(3):393–437. doi: 10.1002/cne.901250308. [DOI] [PubMed] [Google Scholar]
  4. DEWEY M. M., BARR L. A STUDY OF THE STRUCTURE AND DISTRIBUTION OF THE NEXUS. J Cell Biol. 1964 Dec;23:553–585. doi: 10.1083/jcb.23.3.553. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. GOLDMAN L. THE EFFECTS OF STRETCH ON CABLE AND SPIKE PARAMETERS OF SINGLE NERVE FIBRES; SOME IMPLICATIONS FOR THE THEORY OF IMPULSE PROPAGATION. J Physiol. 1964 Dec;175:425–444. doi: 10.1113/jphysiol.1964.sp007525. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. GRUNDFEST H., KAO C. Y., ALTAMIRANO M. Bioelectric effects of ions microinjected into the giant axon of Loligo. J Gen Physiol. 1954 Nov 20;38(2):245–282. doi: 10.1085/jgp.38.2.245. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. HAMA K. Some observations on the fine structure of the giant nerve fibers of the earthworm, Eisenia foetida. J Biophys Biochem Cytol. 1959 Aug;6(1):61–66. doi: 10.1083/jcb.6.1.61. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. HODGKIN A. L., KEYNES R. D. Movements of labelled calcium in squid giant axons. J Physiol. 1957 Sep 30;138(2):253–281. doi: 10.1113/jphysiol.1957.sp005850. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Imanaga I. Cell-to-cell diffusion of procion yellow in sheep and calf Purkinje fibers. J Membr Biol. 1974;16(4):381–388. doi: 10.1007/BF01872425. [DOI] [PubMed] [Google Scholar]
  10. KAO C. Y., GRUNDFEST H. Postsynaptic electrogenesis in septate giant axons. I. Earthworm median giant axon. J Neurophysiol. 1957 Nov;20(6):553–573. doi: 10.1152/jn.1957.20.6.553. [DOI] [PubMed] [Google Scholar]
  11. Kolodny G. M. Evidence for transfer of macromolecular RNA between mammalian cells in culture. Exp Cell Res. 1971 Apr;65(2):313–324. doi: 10.1016/0014-4827(71)90007-3. [DOI] [PubMed] [Google Scholar]
  12. Matter A. A morphometric study on the nexus of rat cardiac muscle. J Cell Biol. 1973 Mar;56(3):690–696. doi: 10.1083/jcb.56.3.690. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. McNutt N. S., Weinstein R. S. The ultrastructure of the nexus. A correlated thin-section and freeze-cleave study. J Cell Biol. 1970 Dec;47(3):666–688. doi: 10.1083/jcb.47.3.666. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Subak-Sharpe H., Bürk R. R., Pitts J. D. Metabolic co-operation between biochemically marked mammalian cells in tissue culture. J Cell Sci. 1969 Mar;4(2):353–367. doi: 10.1242/jcs.4.2.353. [DOI] [PubMed] [Google Scholar]
  15. Weidmann S. Electrical constants of trabecular muscle from mammalian heart. J Physiol. 1970 Nov;210(4):1041–1054. doi: 10.1113/jphysiol.1970.sp009256. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Weidmann S. The diffusion of radiopotassium across intercalated disks of mammalian cardiac muscle. J Physiol. 1966 Nov;187(2):323–342. doi: 10.1113/jphysiol.1966.sp008092. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Weingart R. The permeability to tetraethylammonium ions of the surface membrane and the intercalated disks of sheep and calf myocardium. J Physiol. 1974 Aug;240(3):741–762. doi: 10.1113/jphysiol.1974.sp010632. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from The Journal of General Physiology are provided here courtesy of The Rockefeller University Press

RESOURCES