Diluting power of thick limbs of Henle. II. Bumetanide-sensitive 22Na+ influx in medullary vesicles.
We evaluated the effects of osmotic gradients on 22Na+ influx in vesicles prepared from rat outer renal medulla. 22Na+ influx driven in a coflow mode by an inwardly directed 100 mM KCl gradient was measured at 20 and 60 s; 1 mM bumetanide inhibited approximately 30% of 22Na+ influx. The bumetanide-sensitive 22Na+ influx was reduced by approximately 65% when either K+ or Cl- was omitted from the aqueous phases. We found that an osmotic gradient for vesicle shrinkage, that is, 600 mM urea in the extravesicular medium, enhanced the bumetanide-sensitive 22Na+ influx twofold. Conversely, an osmotic gradient for vesicle swelling, that is, with vesicles but not extravesicular media loaded with 600 mM urea, produced a 50% suppression of bumetanide-sensitive 22Na+ influx. Moreover, 600 mM extravesicular urea, an osmotic gradient for vesicle shrinkage, also reduced uptake of the nonspecific marker [14C]mannitol. These effects of osmotic gradients were not due to alterations in ionic driving forces, since bumetanide-sensitive 22Na+ influx driven in a counterflow mode by loading the vesicles with 100 mM NaCl also was activated or suppressed by osmotic gradients for vesicle shrinkage or swelling, respectively. We conclude that osmotic gradients, and/or vesicle volume changes, modulate bumetanide-sensitive Na+:K+:2Cl- activity.
Reeves
W B
WB
Department of Internal Medicine, University of Texas Medical School, Houston 77225.
Dudley
M A
MA
Mehta
P
P
Andreoli
T E
TE
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002034:Bumetanide / Q000378:metabolism / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004232:Diuretics / Q000494:pharmacology*; D007679:Kidney Medulla / Q000187:drug effects / Q000502:physiology*; D007684:Kidney Tubules / Q000502:physiology*; D008138:Loop of Henle / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D012979:Sodium Radioisotopes; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D004232:Diuretics; D015222:Sodium Channels; D012979:Sodium Radioisotopes; D002034:Bumetanide; D012964:Sodium; D000469:Alkaline Phosphatase; D000254:Sodium-Potassium-Exchanging ATPase