ISSN:
1432-136X
Keywords:
Renal acidification
;
Na+/H+ exchange
;
Proximal tubule
;
Amiloride
;
Brush border membrane vesicles
;
Squalus acanthias
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary A membrane fraction, rich in brush border membranes, was prepared from renal proximal tubules of the spiny dogfish,Squalus acanthias, and the sodium-proton exchange mechanism in these membrane vesicles was investigated by both a rapid filtration technique and the fluorescence quenching of acridine organe.22Na+ uptake was stimulated by an outwardly directed H+ gradient, and was inhibited by amiloride at a single inhibitory site with an apparentK i of approximately 1.7×10−5 M. In the presence of an H i + 〉H o + gradient, the $$K_{{\text{m}}_{{\text{Na}}} + } {\text{and}} V_{\max _{{\text{Na}}} + } $$ of the Na+/H+ exchanger were 9.7±0.8 mM and 48.0±12.0 nmol·mg protein−1·min−1, respectively. The uptake of Na+ was electroneutral in the presence of a H+ gradient, indicating a stoichiometry of 1. In the fluorescence studies, quenching of acridine orange occurred in the presence of an outwardly directed Na+ gradient which was inhibited by amiloride. Thus, an electroneutral Na+/H+ exchanger with properties similar to those found in the mammalian kidney is also present in the spiny dogfish and may contribute to the urinary acidification of this marine animal.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00691514
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