AJP - Cell Physiology, Vol 254, Issue 1 C141-C149, Copyright © 1988 by American Physiological Society
Calcium diffusion through perineurium of frog sciatic nerve
K. C. Wadhwani, H. Levitan and S. I. Rapoport
Laboratory of Neurosciences, National Institute on Aging, Bethesda, Maryland 20892.
Calcium and sucrose permeabilities (PCa or Psucrose) were calculated from
the fluxes of 45Ca and [3H]sucrose across perfused everted and normal
configurations of the perineurial cylinder isolated from the frog sciatic
nerve and from fluxes into an intact nerve segment bathed in Ringer. Mean
PCa for influx across the isolated perineurium equaled 10.2 +/- 0.6 X
10(-7) cm/s (n = 16) compared with Psucrose = 7.4 +/- 0.4 X 10(-7) cm/s.
For efflux, PCa = 27.5 +/- 5.0 X 10(-7) cm/s and Psucrose = 23.2 +/- 4.7 X
10(-7) cm/s. The mean ratio of PCa for efflux to PCa for influx (2.7 +/-
0.5) was not significantly different from the flux ratio for sucrose (3.1
+/- 0.7). No effect on PCa or Psucrose was observed when the calcium
concentration in the bath was varied from 0.5 to 20 mM, when Na-free Ringer
was perfused, or when ouabain, La3+, or 2,4-dinitrophenol was applied.
Asymmetrical fluxes across the perineurial cylinder were due presumably to
bulk flow and resultant solvent drag out of the lumen caused by perfusion
pressure. Calcium accumulated in the perineurial tissue in a saturable
manner with a Km of 80 microM and a Bmax of 0.22 mumol/g wet wt. The half
time for calcium exchange from the external medium to the nerve was
calculated as 3 h. This long half time and the calcium-sequestering ability
of the perineurium suggest that the perineurium can stabilize endoneurial
calcium during transient changes in the calcium concentration of plasma.
