Overview Topics |
Diffusion of Molecules:
Molecule Type |
Molecular weight |
Diffusion Coefficient |
Effective
Diffusivity |
Ref |
3-4 kD |
5 x 10 –7 cm2/s = 3000 microns2 / min |
1500 microns2
/ min |
Goodhill (97) |
|
17 kD |
3 x 10 –7 cm2/s = 1800 microns2 / min |
900 microns2
/ min |
Goodhill (97) |
|
26 kD |
2.7 x 10 –7 cm2/s = 1620 microns2 / min |
810 microns2
/ min |
Goodhill (97); Moghe et al (95) |
|
TGF-Beta |
25 kD |
2.6 x 10 –7 cm2/s = 1560 microns2 / min |
780 microns2
/ min |
Brown (99) |
17 kD |
3 x 10 –7
cm2/s = 1800 microns2 / min |
900 microns2 / min |
|
The diffusion coefficient scales approximately as the inverse of the cube root of the
molecular weight. A molecule of mw 0.3-0.5 kDa has a diffusion coefficient of
approximately 10 –6 cm2/s
. We also use the fact that 10 – 7 cm2/s = 600 microns2
/ min.
[1] Goodhill G J (1998) Mathematical Guidance
for axons, Trends Neurosci 21, 226-231. Abstract
[2] Goodhill J G (1997) Diffusion in axon
guidance, Eur J Neurosci 9: 1414-1412.Abstract
02/17/00 Update:
We have recently become aware of the correction factor that needs to be
incorporated in the above calculations due to the tortuosity of the neuronal
extracellular space. The effective diffusion coefficients cited above are
calculated using the references provided by E. Sykova, for example:
[3] Sykova E (1997) The extracellular space
in the CNS: Its regulation, volume, and geometry in normal and pathological
neuronal function, The Neuroscientist 3(1): 28-41.Abstract
[4] Mazel T, Simonova Z, Sykova E (1998)
Diffusion heterogeneity and anisotripy in rat hippocampus, NeuroReport 9:
1299-1304. Abstract
[5] Sykova E, T Mazel, Z Simonova (1998)
Diffusion constraints and neuron-glia interaction during aging Experimental
Gerontology 33 (7/8) : 837-851. Abstract
[6] Nicholson C, Sykova E (1998)
Extracellular space structure revealed by diffusion analysis TINS 21 (5) :
207-215.Abstract
See also more information at the Sykova Lab Home page.
Information about molecular weights and other attributes of of cytokines were
obtained from the site :
[7] Signaling Pathway mediated by IL-6 and IL-1, The Signaling PAthway Database (SPAD), Molecular
Gene Technics, Kyushu University, Japan