Ionic permeabilities of the frog perineurium.

Area of Science:

• Neuroscience
• Physiology
• Biophysics

Background:

• The perineurium forms a crucial diffusion barrier around peripheral nerves.
• Understanding its permeability is key to nerve function and drug delivery.

Purpose of the Study:

• To investigate ionic permeation across the frog sciatic nerve perineurium.
• To assess the impact of hypertonic solutions and specific drugs on perineurial permeability.

Main Methods:

• In vitro perfusion of isolated frog sciatic nerve perineurial segments.
• Measurement of 22Na, 42K, and 36Cl ion fluxes.
• Assessment of [14C]sucrose permeability under varying conditions.

Main Results:

• Perineurial permeability to Na+ and K+ was unaffected by hypertonic Ringer, ouabain, or amiloride.
• Hypertonic treatment increased absolute ion permeability but not permeability ratios.
• The perineurium exhibits size-dependent permselectivity, similar to epithelia with tight junctions.

Conclusions:

• The frog sciatic nerve perineurium functions as a passive diffusion barrier.
• Evidence suggests a size-selective paracellular pathway, not active ion transport.
• Permeability coefficients quantify the perineurium's barrier properties for ions and non-electrolytes.