Calcium diffusion through perineurium of frog sciatic nerve

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Abstract
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.