Skip to main content
PMC home page
The Journal of General Physiology logoLink to The Journal of General Physiology
. 1962 Nov 1;46(2):245–255. doi: 10.1085/jgp.46.2.245

Diffusion Barriers in the Squid Nerve Fiber

The axolemma and the Schwann layer

Raimundo Villegas 1, Carlo Caputo 1, Leopoldo Villegas 1
PMCID: PMC2195262  PMID: 13997307

Abstract

The squid nerve barriers are formed by (a) the axolemma (membrane of the axon proper), a membrane 80 Å thick perforated by cylindrical pores 4.0 to 4.5 Å radius, and (b) the Schwann layer, constituted of numerous cells forming a layer one cell thick, crossed by 60 Å wide slit channels. If a molecule present in the axoplasm has to reach the extraneural space, it has to pass (a) the pores, and (b) the channels, in series, and the diffusion rate will depend on the effective diffusion areas per unit path length, Apd/Δx for the axolemma, and Acd/Δx for the Schwann layer. By addition, And/Δx, the transneural effective area for diffusion per unit path length is obtained. The diffusion rates of C14-ethylene glycol (2.2 Å radius), and C14-glycerol (2.8 Å radius) were measured. The diffusion rate of H3-labeled water (1.5 Å radius) has been previously determined. The results expressed in terms of And/Δx (mean values ± SD, referred to 1 cm2 of nerve surface) are 5.3 ± 1.4 cm for water, 2.5 ± 0.4 cm for ethylene glycol, and 0.29 ± 0.03 cm for glycerol. Theoretical values for And/Δx of 2.5 and 0.83 cm for ethylene glycol and glycerol have been calculated. The agreement between the theoretical values for And/Δx and the experimental ones supports the diffusion barrier model described above.

Full Text

The Full Text of this article is available as a PDF (680.1 KB).

Selected References

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

  1. CURRAN P. F. Na, Cl, and water transport by rat ileum in vitro. J Gen Physiol. 1960 Jul;43:1137–1148. doi: 10.1085/jgp.43.6.1137. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. DAINTY J., KRNJEVIC K. The rate of exchange of 24Na in cat nerves. J Physiol. 1955 Jun 28;128(3):489–503. doi: 10.1113/jphysiol.1955.sp005320. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. DURBIN R. P. Osmotic flow of water across permeable cellulose membranes. J Gen Physiol. 1960 Nov;44:315–326. doi: 10.1085/jgp.44.2.315. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. HODGKIN A. L., KEYNES R. D. Active transport of cations in giant axons from Sepia and Loligo. J Physiol. 1955 Apr 28;128(1):28–60. doi: 10.1113/jphysiol.1955.sp005290. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. KEDEM O., KATCHALSKY A. A physical interpretation of the phenomenological coefficients of membrane permeability. J Gen Physiol. 1961 Sep;45:143–179. doi: 10.1085/jgp.45.1.143. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. LEAF A. The mechanism of the asymmetrical distribution of endogenous lactate about the isolated toad bladder. J Cell Comp Physiol. 1959 Aug;54:103–108. doi: 10.1002/jcp.1030540111. [DOI] [PubMed] [Google Scholar]
  7. NEVIS A. H. Water transport in invertebrate peripheral nerve fibers. J Gen Physiol. 1958 May 20;41(5):927–958. doi: 10.1085/jgp.41.5.927. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. RENKIN E. M. Filtration, diffusion, and molecular sieving through porous cellulose membranes. J Gen Physiol. 1954 Nov 20;38(2):225–243. [PMC free article] [PubMed] [Google Scholar]
  9. VILLEGAS R., BARNOLA F. V. Characterization of the resting axolemma in the giant axon of the squid. J Gen Physiol. 1961 May;44:963–977. doi: 10.1085/jgp.44.5.963. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. WHITTEMBURY G. Action of antidiuretic hormone on the equivalent pore radius at both surfaces of the epithelium of the isolated toad skin. J Gen Physiol. 1962 Sep;46:117–130. doi: 10.1085/jgp.46.1.117. [DOI] [PMC free article] [PubMed] [Google Scholar]

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

RESOURCES