Direct evidence for the absence of active Na+ reabsorption in hamster ascending thin limb of Henle's loop.
The mechanisms of Na+ transport across cell membranes were investigated in the in vitro microperfused hamster ascending thin limb (ATL) of Henle's loop using a fluorescent Na+ indicator sodium-binding benzofuran isophthalate. The intracellular Na+ concentration ([Na+]i) of the ATL cells was 17.1 +/- 1.7 mM (n = 22) when the ATL was microperfused in vitro with Hepes-buffered solution containing 204 mM Na+. Elimination of metabolites such as glucose and alanine from the basolateral solution increased [Na+]i. Applying either 5 mM cyanide or 5 mM iodoacetic acid to the bath also increased [Na+]i. The elimination of K+ and the addition of 10(-4) M ouabain in the bath increased [Na+]i by 25.0 +/- 5.0 mM (n = 5) in 3 min and by 10.7 +/- 2.4 mM (n = 4), respectively. The elimination of luminal and basolateral Na+ resulted in a decrease in [Na+]i, indicating Na+ permeability of both the luminal and basolateral cell membranes. The luminal Na+ permeability was not affected by furosemide. The presence of luminal Na+ permeability and the basolateral Na+/K+ ATPase suggests the presence of net active reabsorption of Na+, which is not a physiologically important amount, in our estimation.
Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan.
Y
Y
Kondo
K
K
Abe
Y
Y
Igarashi
K
K
Kudo
K
K
Tada
K
K
Yoshinaga
D000409:Alanine / Q000494:pharmacology; D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D006224:Cricetinae; D003486:Cyanides / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D066298:In Vitro Techniques; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D007684:Kidney Tubules / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D008647:Mesocricetus; D008954:Models, Biological; D010477:Perfusion; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D003486:Cyanides; D007461:Iodoacetates; D000666:Amphotericin B; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose; D000409:Alanine; D019807:Iodoacetic Acid