ISSN:
1432-2013
Keywords:
SITS
;
Probenecid
;
Phloretin
;
Acetazolamide
;
Lactate
;
Renal tubule
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The transport ofd-lactate across the epithelium of the late proximal convolution was investigated by two methods: 1. by measuring the zero net flux transtubular concentration difference (Δc tt,45s) and the permeability (P) ofd-lactate and calculating from both the transtubular active transport rate (J lac act ). 2. By measuring the 3.5 s efflux ofd-lactate from the tubular lumen, while blood was flowing through the capillaries. The 3.5 s efflux comprises two components, one going through the brush border (J lac bb ) and one going the paracellular pathway (J lac paracell =P lac·c lac lumen). Both,J lac act andJ lac bb ofd-lactate gave the sameK m 1.9 and 1.7 mmol/l and the same maximal transport rate 3.2 and 2.9 pmol cm−1 s−1. TheK i ofl-lactate tested againstJ lac act andJ lac bb ofd-lactate was also the same: 1.1 and 1.0 mmol/l. These data indicate that under our experimental conditions only the flux through the brush border seems to be rate limiting and thatd-lactate uses the same transport system asl-lactate. When Na+ was omitted from the perfusatesJ lac act disappeared completely, whileJ lac bb was reduced by 64%. These data reflect the Na+ dependence of thed-lactate transport through the brush border. Variation of intra-and extracellular pH by raisingpCO2, omitting HCO 3 − from the perfusates or adding acetazolamide had no effect on the transport ofd-lactate when α-ketoglutarate was used as fuel. However, when acetate was used as fuel, intracellular acidosis brought the reducedJ lac act back to the values obtained with α-ketoglutarate as fuel. It is suggested that this is an effect on a contraluminal transport step. Probenecid (5 mmol/l) and phloretin (0.25 mmol/l) inhibitedJ lac act significantly.J lac bb , however, was only inhibited by probenecid when acetate was used as fuel. These data indicate that both compounds act on thed-lactate exit at the contraluminal cell side, but that probenecid acts in addition at the luminal cell side. SITS (1 mmol/l) augmentedJ lac bb when acetate was used as fuel and is similar to the effect of lowering intracellular pH as described above. The SH reagents mersalyl (1.0 mmol/l) and maleolylglycine (1 mmol/l) did not influenceJ lac bb .
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00584812
