Diluting power of thick limbs of Henle. II. Bumetanide-sensitive 22Na+ influx in medullary vesicles

W. B. Reeves, M. A. Dudley, P. Mehta, T. E. Andreoli

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


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 ~ 30% of 22Na+ influx. The bumetanide-sensitive 22Na+ influx was reduced by ~ 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 vesicles shrinkage or swelling, respectively. We conclude that osmotic gradients, and/or vesicle volume changes, modulate bumetanide-sensitive Na+:K+:2Cl- activity.

Original languageEnglish (US)
Pages (from-to)F1138-FF1144
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Issue number6 (24/6)
StatePublished - 1988
Externally publishedYes

ASJC Scopus subject areas

  • Physiology


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