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Calcium diffusion through perineurium of frog sciatic nerve
K C Wadhwani1, H Levitan, S I Rapoport
1Laboratory of Neurosciences, National Institute on Aging, Bethesda, Maryland 20892.
The American Journal of Physiology
|January 1, 1988
Summary
The frog sciatic nerve perineurium regulates calcium and sucrose transport, showing higher permeability for efflux than influx. This tissue can stabilize endoneurial calcium levels during plasma fluctuations.
Area of Science:
- Neuroscience
- Cell Biology
- Physiology
Background:
- The perineurium forms a critical barrier in peripheral nerves.
- Understanding ion and molecule transport across the perineurium is vital for nerve function.
Purpose of the Study:
- To quantify calcium and sucrose permeabilities across the frog sciatic nerve perineurium.
- To investigate factors influencing these transport mechanisms.
- To assess the perineurium's role in regulating endoneurial calcium.
Main Methods:
- Flux measurements of 45Ca and [3H]sucrose across isolated and intact frog sciatic nerve segments.
- Perfusion of everted and normal perineurial cylinder configurations.
- Variations in bathing calcium concentration, sodium-free Ringer, and application of ouabain, La3+, and 2,4-dinitrophenol.
Main Results:
- Mean calcium permeability (PCa) for influx was 10.2 x 10(-7) cm/s and for efflux was 27.5 x 10(-7) cm/s.
- Mean sucrose permeability (Psucrose) for influx was 7.4 x 10(-7) cm/s and for efflux was 23.2 x 10(-7) cm/s.
- Calcium accumulation in perineurial tissue occurred in a saturable manner (Km = 80 microM, Bmax = 0.22 mumol/g wet wt).
- No significant effects on permeabilities were observed with varied calcium concentrations or specific inhibitors.
Conclusions:
- Asymmetrical fluxes suggest bulk flow and solvent drag influence transport.
- The perineurium exhibits calcium-sequestering ability with a long exchange half-time (3 h).
- The perineurium plays a role in stabilizing endoneurial calcium concentrations against transient plasma changes.