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KMID : 0359920070260010005
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Korean Journal of Nephrology
2007 Volume.26 No. 1 p.5 ~ p.13
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Biochemical Characteristics of The Na-α-Ketoglutarate Cotransport System in Proximal Convoluted and Straight Tubules of the Rabbit Kidney
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Ahn Do-Whan
Kim Kyoung-Ryong
Park Hee-Seok
Park Yang-Saeng
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Abstract
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Purpose: alpha-Ketoglutarate (αKG), a Krebs cycle intermediate, is extensively used in the kidney as a fuel substrate and as a counter anion for organic acid secretion. It is known to be taken up by the proximal tubule cells via the brush-border as well as basolateral membranes. We explored biochemical characteristics of the brush-border and basolateral αKG transport systems in pars convoluta and pars recta of the proximal tubule, respectively.
Methods: Brush-border and basolateral membrane vesicles (BBMV and BLMV) were isolated from rabbit renal outer cortex and outer medulla by Percoll gradient centrifugation. Vesicular uptake of αKG was determined by rapid Millipore filtration method using α-14[C]KG as a substrate.
Results: Both BBMV and BLMV showed a Na-gradient dependent uphill transport of αKG. The systems in both membranes were similarly inhibited by Li and activated by Na (Hill coefficient of 1.4). Kinetic analyses indicated that the Na-αKG cotransporters in the BBMV had a lower substrate affinity as compared with those in the BLMV. The transport systems in BLMVs showed a similar Km but different Vmax between the outer cortex (Km: 34 uM, Vmax: 3.3 nmol/mg protein/10s) and outer medulla (Km: 37, Vmax: 1.8). On the other hand, the systems in BBMVs were different in both Km and Vmax between the outer cortex (Km: 194, Vmax: 3.3) and outer medulla (Km: 89, Vmax: 1.7).
Conclusion: The findings suggest that both axial and apical to basolateral heterogeneity of the Na-αKG cotransport system in proximal tubules may be due to a physiological adaptation to efficiently utilize αKG in the kidney.
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KEYWORD
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Symporters, Ketoglutaric acids, Kidney tubules
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