ISSN:
1432-2013
Keywords:
Kidney
;
Tubular resorption
;
Microperfusion
;
Specificity
;
Glutamate
;
Aspartate
;
Cysteate
;
γ-Carboxyglutamate
;
Pyroglutamate
;
5-oxo-proline
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Single sections of superficial proximal convolutions of rat kidney were microperfused in vivo and in situ. The perfusion fluids contained radioactively labelledl- ord-aspartate,l-glutamate,l-pyroglutamate, or N-methyl-d-aspartate.l-γ-Carboxyglutamate as well as the other amino acids were added in the unlabelled from. Results.l- andd-Aspartate (0.073 mmol·1−1) are quickly resorbed at about the same rate.d-Aspartate resorption was blocked byl-aspartate (5 mmol·1−1) but not by β-alanine (5 mmol·1−1).l-Aspartate resorption was inhibited byl-glutamate (2 mmol·1−1) but not byd-glutamate,l-asparagine,l-phenylalanine or by succinate (2 mmol·1−1, each). The fast resorption ofl-glutamate (0.073 mmol·1−1) was blocked byd-aspartate,l-cysteate (2 mmol·1−1), but not by 3-mercaptopicolinic acid (0.15 mmol·1−1),l-glutamine, 2-oxoglutarate, taurine, N-methyl-l-glutamate or kainic acid (2 mmol·1−1, each).l-γ-Carboxyglutamate (0.66 mmol·1−1) and N-methyl-d-aspartate (2μmol·1−1) were found to be resorbed only at an extremely small rate.l-pyroglutamate (0.076 mmol·1−1) resorption was not influenced byl-glutamate (1 mmol·1−1). Fractional excretion of γ-carboxyglutamate was 7–25% (l-from) or 45–70% (d-form) at an artificially elevated plasma level of 12μmol·1−1. It is concluded thatl- andd-aspartate,l-glutamate,l-cysteate and, to a much smaller extent,l-γ-carboxyglutamate, are accepted by the tubular resorption mechanism highly specific for “acidic” amino acids. N-Substitution, the amidation of the β- or γ-carboxyl group, or the removal of the α-amino moiety almost completely abolish the ability of such compounds to be resorbed via this carrier; N-methylated or γ-carboxylated derivatives of “acidic” amino acids are not resorbed at all from the proximal tubule. The resorption of glutamate, but not of aspartate, is highly stereospecific.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00587859
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