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Effects of Cl- transport inhibitors on Cl- permeability across hamster ascending thin limb
T Isozaki1, K Yoshitomi, M Imai
1Department of Pharmacology, National Cardiovascular Center, Osaka, Japan.
Insights
The ascending thin limb (ATL) utilizes a highly conductive chloride (Cl-) transport pathway. Researchers found that 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) significantly inhibits Cl- permeability in the ATL.
Area of Science:
- Nephrology
- Renal Physiology
- Ion Transport
Background:
- The ascending thin limb (ATL) of Henle's loop is crucial for renal concentrating mechanisms.
- A highly conductive chloride (Cl-) transport pathway is known to exist in the ATL.
Purpose of the Study:
- To investigate the mechanism of Cl- conductance in the ATL.
- To characterize the effects of specific Cl- transport inhibitors on ATL permeability.
Main Methods:
- In vitro microperfusion technique was used to study hamster ATL.
- Examined the effects of 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), diphenylamine carboxylate (DPC), and anthracene-9-carboxylic acid (9-AC) on Cl- permeability.
- Measured relative permeability of Cl- to Na+ (PCl/PNa) and lumen-to-bath flux coefficient for 36Cl.
Main Results:
- NPPB reversibly suppressed PCl/PNa in a dose-dependent manner when added to the bath.
- The concentration of NPPB inhibiting 50% of PCl/PNa (ID50) was approximately 3 X 10(-5) M.
- NPPB was a more potent inhibitor of PCl/PNa than 9-AC or DPC.
Conclusions:
- NPPB effectively inhibits the Cl- conductance pathway in the ATL.
- The findings provide insights into the molecular mechanisms of Cl- transport in the kidney's concentrating segment.
Abstract:
The highly conductive Cl- transport pathway exists in the ascending thin limb (ATL) of Henle's loop. To characterize the mechanism of the Cl- conductance across the ATL, we examined effects on Cl- permeability across hamster ATL of Cl- transport inhibitors, including 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), diphenylamine carboxylate (DPC), and anthracene-9-carboxylic acid (9-AC), by the in vitro microperfusion technique. NPPB added to the bath caused reversible suppression of the relative permeability of Cl- to Na+ (PCl/PNa), as estimated from the NaCl diffusion voltage in a dose-dependent manner in a range from 3 x 10(-6) to 10(-3) M. The concentration of NPPB that inhibited PCl/PNa by 50% (ID50) was approximately 3 X 10(-5) M. When 3 X 10(-5) M NPPB was added to the bath, the lumen-to-bath flux coefficient for 36Cl (Kl----b,Cl- 10(-7) cm2/s) was decreased from 130.7 +/- 7.3 to 52.2 +/- 11.6 (n = 7, P less than 0.01). Application of NPPB in the lumen also caused reversible suppression of PCl/PNa, but this effect was less potent compared with the application of the drug via the bath. Whereas 10(-3) M 9-AC or 10(-3) M DPC decreased PCl/PNa by 6.5 +/- 1.2 and 10.2 +/- 2.6%, respectively, 3 X 10(-4) M NPPB decreased PCl/PNa by 69.7 +/- 3.8%. In maleimide-treated tubules, addition of 10(-3) M N-ethylmaleimide (NEM) increased PCl/PNa from 1.0 +/- 0.1 to 1.8 +/- 0.1 (n = 7, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)