AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 2 284-R288, Copyright © 1992 by American Physiological Society
Saturable transport of manganese(II) across blood-nerve barrier of rat peripheral nerve
K. C. Wadhwani, V. A. Murphy, Q. R. Smith and S. I. Rapoport
Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892.
To determine whether the blood-nerve barrier of the rat peripheral nerve
transports manganese(II) (Mn) by a saturable mechanism similar to that
found at the blood-brain barrier, we measured the uptake of 54Mn from blood
into desheathed sciatic nerve and into cerebral cortex of awake rats at
different plasma concentrations of unlabeled Mn using an intravenous
infusion technique. The unidirectional influx (Jin) of Mn into sciatic
nerve was facilitated and saturable, when steady-state plasma Mn ranged
from 4 to 4,312 ng/ml (0.073-78.4 microM), as was the unidirectional influx
of Mn into the cerebral cortex. Michaelis-Menten constants (Km and Vmax)
and the passive diffusion constant (Kd), determined by nonlinear least
squares, were as follows: for the blood-nerve barrier (sciatic nerve) Km =
4.7 microM, Vmax = 0.56 x 10(-3) nmol.s-1.g wet wt-1, and Kd = 6.3 x 10(-6)
ml.s-1.g wet wt-1; for the blood-brain barrier (cerebral cortex) Km = 1.0
microM, Vmax = 0.40 x 10(-3) nmol.s-1.g wet wt-1, and Kd = 0.3 x 10(-6)
ml.s-1.g wet wt-1. The results demonstrate facilitated
concentration-dependent mechanisms of transport of Mn at the blood-nerve
and blood-brain barriers.
