Sodium-taurine cotransport in reptilian renal brush-border membrane vesicles.
The coupled transport of Na+ with taurine into snake renal brush-border membrane vesicles (BBMV) was studied using 5-s uptake conditions. Taurine transport into snake renal BBMV involved two parallel processes, one saturable (Na(+)-dependent) and one (Na(+)-independent) that behaved like passive diffusion. Below 1 mM taurine concentration, the Na(+)-dependent system accounted for 60% of total taurine uptake. Over both low (0.001-0.80 mM) and high (0.8-5.0 mM) taurine concentration ranges, the Na(+)-dependent taurine uptake within each range showed Michaelis-Menten kinetics, suggesting the presence of two independent saturable Na(+)-dependent transport systems for taurine. The high-affinity, low-capacity system saturated above 100 microM with a Km of 71.4 +/- 45.7 microM and a maximum velocity (Vmax) of 21.9 +/- 3.77 pmol (mg protein)-1 (5 s)-1. The low-affinity, high-capacity system saturated above 1 mM, with a Km of 1.11 +/- 0.63 mM and a Vmax of 252 +/- 47 pmol (mg protein)-1 (5 s)-1. The stoichiometric relationship between external Na+ concentration and taurine uptake (at 10 microM) by the high-affinity BBMV transport system was examined by the activation method under short-circuited conditions. The 5-s rate of taurine transport was a sigmoid function of increasing extravesicular Na+ concentration. Kinetic analysis of the interaction of Na+ with the high-affinity taurine transport system suggested that 3 Na+ ions (3.2 +/- 0.7) may be involved with 1 taurine molecule in the transport event.(ABSTRACT TRUNCATED AT 250 WORDS)
Benyajati
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Department of Physiology and Biophysics, College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City 73190.
Bay
S M
SM
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism*; D012911:Snakes / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism*
D000596:Amino Acids; D013654:Taurine; D012964:Sodium