title: Inhibition of glutamate uptake causes an acute increase in aqueous humor protein.
abstract: Inhibition of glutamate transport has been shown to increase paracellular permeability of epithelial cell monolayers in vitro. To determine if blocking glutamate transport would affect tissue permeability in vivo, D-aspartate (D-Asp; 300 nmol 30 microliters-1) (a non-toxic competitive inhibitor of glutamate transport) or a placebo was injected into the anterior chambers of the fellow eyes of 15 adult rabbits. [14C]-L-glucose and/or [125I]-rabbit albumin were included in the injection vehicle as aqueous humor (AH) outflow markers. The specific inhibition of glutamate uptake by D-Asp was indicated by a 15% increase in AH glutamate (174 +/- 9 nmol ml-1 to 205 +/- 13 nmol ml-1; P = 0.03) at 1-1.5 hr post injection. Also, the efflux of [14C]-L-glucose and [125I]-rabbit albumin from the AH of D-Asp injected eyes was increased 22% over the placebo-injected control eyes (P < or = 0.02). Concomitantly, the total protein concentration in the AH from D-Asp injected eyes (517 +/- 35 micrograms ml-1) was 19% greater (P < 0.02) than the protein concentration in AH from placebo-injected control eyes (420 +/- 36 micrograms ml-1). In additional studies, an irreversible inhibitor of glutamate transport, threo-beta-hydroxyaspartate (THA; 30 nmol 30 microliters-1), was shown to increase the efflux of [14C]-L-glucose (22%; P < 0.05) from the anterior chamber and increase AH protein concentrations by 29% (484 +/- 112 micrograms ml-1 in control AH versus 686 +/- 117 micrograms ml-1 in THA AH, P = 0.08) at 1 hr post intracameral injection. SDS-PAGE analysis of the AH associated the protein increase in the D-Asp and THA injected eyes but not placebo-injected control eyes with a detectable increase in a 66 kDa protein (aligns with serum albumin) and several lower molecular weight (23-35 kDa) AH proteins. The results found suggest that inhibition of glutamate transport from the AH acutely increases intraocular epithelial/endothelial paracellular permeability.
authors.affiliation: Department of Ophthalmology, Louisiana State University Medical Center, Shreveport, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Langford
authors.forename: M E
authors.initials: ME
authors.lastname: Berg
authors.forename: J H
authors.initials: JH
authors.lastname: Mack
authors.forename: J P
authors.initials: JP
authors.lastname: Ganley
authors.forename: T C
authors.initials: TC
authors.lastname: Welbourne
mesh_terms: D000409:Alanine / Q000378:metabolism; D000818:Animals; D001082:Aqueous Humor / Q000187:drug effects* / Q000378:metabolism; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005136:Eye Proteins / Q000032:analysis / Q000378:metabolism*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D008297:Male; D011817:Rabbits
chemical_list: D018691:Excitatory Amino Acid Antagonists; D005136:Eye Proteins; D005973:Glutamine; C011274:3-hydroxyaspartic acid; D001224:Aspartic Acid; D018698:Glutamic Acid; D000409:Alanine