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Transport of Zinc‐65 at the Blood‐Brain Barrier During Short Cerebrovascular Perfusion in the Rat: Its Enhancement by Histidine
Author(s) -
BuxaniRice S.,
Ueda F.,
Bradbury M. W. B.
Publication year - 1994
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1994.62020665.x
Subject(s) - blood–brain barrier , perfusion , histidine , zinc , chemistry , medicine , neuroscience , central nervous system , biochemistry , biology , organic chemistry , amino acid
Zinc‐65 transport into different regions of rat brain has been measured during short vascular perfusion of one cerebral hemisphere with an oxygenated HEPES‐containing physiological saline at pH 7.40. The [Zn 2+ ] was buffered with either bovine serum albumin or histidine. In each case uptake was linear with time up to 90 s. 65 Zn flux into brain in the presence of albumin followed Michaelis‐Menten kinetics and for parietal cortex had a K m of 16 n M and a V max of 44 nmol/kg/min. Increasing concentrations of l ‐histidine enhanced 65 Zn flux into brain at [Zn 2+ ] values between 1 and 1,000 n M . The combined effect of [histidine] and [Zn 2+ ] was best accounted for by a function of [ZnHis + ], i.e., flux = 64.4 · [ZnHis + ]/(390 + [ZnHis + ]) + 0.00378 · [ZnHis + ], with concentrations being nanomolar. d ‐Histidine had an influence similar to that of l ‐histidine. 65 Zn flux in the presence of 100 µ M l ‐histidine was not affected by either 500 µ M l ‐arginine or 500 µ M l ‐phenylalanine. The results indicate specific transport of Zn 2+ across the plasma membranes of brain endothelium. The enhancement due to histidine has been attributed to diffusion of ZnHis + across unstirred layers “ferrying” zinc to and from transport sites.