Thiazide-sensitive Na-Cl cotransport mediates NaCl absorption in amphibian distal tubule.
To find out the mechanism(s) underlying NaCl absorption in the distal tubule of Necturus, we devised a variant of the split-drop technique. Following injection an oil column, subsequently split by a NaCl solution isotonic to plasma, a double-barrelled microelectrode (conventional/selective to Na+ or to Cl- ions) recorded Na+ (alpha Na) or Cl- (alpha Cl) activity and transepithelial potential (Vte). Paired control/low-Na+ solutions yielded reabsorptive half-times (t1/2) of 0.68 +/- 0.11 min and 7.6 +/- 1.8 min respectively; corresponding Vte values were -22.2 +/- 4.0 mV and -7.6 +/- 1.9 mV. t1/2 values of control versus low-Cl- solutions were 0.77 +/- 0.32 min and 6.5 +/- 1.7 min respectively, whereas respective Vte values were not different from one another: -23.8 +/- 4.3 mV versus -18.8 +/- 5.5 mV. Nominally K(+)-free solutions or bumetanide, 10 mumol/l, did not alter t1/2 or Vte, with regard to the paired control. Amiloride, 5 mumol/l or 2 mmol/l, failed to decrease t1/2 or to lower Vte; apparently, the role of a Na+/H+ antiport does not contribute significantly to NaCl absorption. Furosemide, 0.1 mmol/l, reduced t1/2 by 54% with regard to the control state. Determination of t1/2 as a function of increasing hydrochlorothiazide concentrations revealed apical high- and low-affinity sites, estimated at 0.56 mumol/l and 0.115 mmol/l respectively. Taken together these observations indicate that NaCl absorption is predominantly carried out by an electroneutral Na(+)-Cl- cotransport.
Planelles
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G
INSERM U.323, Faculté Necker Enfants-Malades, Paris, France.
Anagnostopoulos
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T
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000187:drug effects / Q000502:physiology*; D005665:Furosemide / Q000494:pharmacology; D006852:Hydrochlorothiazide / Q000494:pharmacology; D007686:Kidney Tubules, Distal / Q000187:drug effects / Q000378:metabolism*; D009337:Necturus; D012965:Sodium Chloride / Q000493:pharmacokinetics*; D049992:Sodium Chloride Symporters; D027981:Symporters
D002352:Carrier Proteins; D049992:Sodium Chloride Symporters; D027981:Symporters; D006852:Hydrochlorothiazide; D002034:Bumetanide; D012965:Sodium Chloride; D000584:Amiloride; D005665:Furosemide