High potassium selective permeability and extracellular ion regulation in the glial perineurium (blood-brain barrier) of the crayfish.
Selective ion permeability, ion transport properties, and electrical resistance of the perineurial barrier, as they relate to interstitial ion regulation, where studied and characterized electrophysiologically in ion substitution experiments. In high external [K+] a transient spike-like voltage was generated across the perineurial barrier which fell over 1-2 min to a slowly decaying voltage. The glial perineurium had at least a 10 times greater permeability to K+ than Cl-, and was effectively impermeant to Na+. The potential, in high external [K+], was determined by the K+ and Cl- gradients and their relative permeabilities across the sheath. For other cations the selectivity sequence of the perineurial barrier, as determined from electrophysiological measurements, was K+ greater than or equal to Rb+ much greater than NH4+ greater than Cs+ greater than Li+ greater than Na+ corresponding most closely to the Eisenman sequence IV. The perineurium had a resistance of 260 +/- 23 omega cm2 in crayfish physiological solution. In high [K+]0 the resistance fell by over half during the transient spike potential and then recovered towards resting levels as the voltage decayed. In the intact nerve cord interstitial [K+] rose to only 10-20 mM during a 2-min exposure to 100 mM K0+. K influx and efflux were related to the change in barrier permeability and an increased selectivity to K+ which, in these studies, was determined primarily by its electrochemical gradient across the perineurial barrier. The results suggest that the crayfish perineurium is a leaky epithelium capable of a high degree of ion regulation. Trans-perineurial barrier potential and conductance in high external [K+] are primarily functions of passive processes of the perineurial glial cell membranes and of the paracellular conductance channels driven by the electrochemical gradient for the K+. Accordingly, the mass transport of [K+] showed the same quantitative relationship in both directions.
Hargittai
P T
PT
Department of Physiology, School of Medicine, East Carolina University, Greenville, NC 27858.
Butt
A M
AM
Lieberman
E M
EM
D000818:Animals; D003400:Astacoidea / Q000378:metabolism*; D001692:Biological Transport; D001812:Blood-Brain Barrier; D002463:Cell Membrane Permeability; D004563:Electrochemistry; D004594:Electrophysiology / Q000295:instrumentation; D005110:Extracellular Space / Q000378:metabolism*; D007477:Ions; D009457:Neuroglia / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D013997:Time Factors
D007477:Ions; D011188:Potassium