title: Saturable transport of manganese(II) across blood-nerve barrier of rat peripheral nerve.
abstract: 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.
authors.affiliation: Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: K C
authors.initials: KC
authors.lastname: Wadhwani
authors.forename: V A
authors.initials: VA
authors.lastname: Murphy
authors.forename: Q R
authors.initials: QR
authors.lastname: Smith
authors.forename: S I
authors.initials: SI
authors.lastname: Rapoport
mesh_terms: D000818:Animals; D001692:Biological Transport; D002540:Cerebral Cortex / Q000378:metabolism; D008297:Male; D008345:Manganese / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics*; D008433:Mathematics; D009132:Muscles / Q000378:metabolism; D009994:Osmolar Concentration; D051381:Rats; D011916:Rats, Inbred F344; D012044:Regression Analysis; D012584:Sciatic Nerve / Q000098:blood supply / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism
chemical_list: D008345:Manganese