title: Transport of sodium and urea in outer medullary descending vasa recta.
abstract: We dissected and perfused outer medullary vasa recta (OMVR) from vascular bundles in the rat. Permeabilities of sodium (PNa) and urea (Pu) were simultaneously determined from the lumen-to-bath efflux of 22Na and [14C]urea. PNa and Pu were also measured by in vivo microperfusion of descending (DVR) and ascending vasa recta (AVR) at the papillary tip of Munich-Wistar rats. In some OMVR PNa was indistinguishable from zero. The mean +/- SE of PNa (x 10(-5), cm/s) in OMVR was 76 +/- 9. Pu in OMVR was always very high (x 10(-5), cm/s), 360 +/- 14. There was no correlation between OMVR PNa and Pu. Inner medullary AVR and DVR had PNa of 115 +/- 10 and 75 +/- 10, respectively, and Pu of 121 +/- 10 and 76 +/- 11, respectively. PNa and Pu in papillary vasa recta were always nearly identical and highly correlated. Transport of [14C] urea in OMVR was reversibly inhibited by addition of unlabeled urea or phloretin to the bath and lumen, providing evidence for carrier-mediated transport. These data suggest that sodium and urea might traverse the wall of inner medullary vasa recta by a paracellular pathway while urea also crosses by a transcellular route in OMVR. Electron microscopic examination of seven in vitro perfused OMVR revealed no fenestrations and exposure of these vessels to 10 microM calcium ionophore A23187 or 1 nM angiotensin II resulted in reversible contraction, suggesting that in vitro perfused OMVR are DVR only.
authors.affiliation: Division of Nephrology, M.S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
authors.forename: T L
authors.initials: TL
authors.lastname: Pallone
authors.forename: J
authors.initials: J
authors.lastname: Work
authors.forename: R L
authors.initials: RL
authors.lastname: Myers
authors.forename: R L
authors.initials: RL
authors.lastname: Jamison
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D000001:Calcimycin / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000648:ultrastructure; D017629:Gap Junctions / Q000648:ultrastructure; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000098:blood supply*; D007700:Kinetics; D008564:Membrane Potentials; D008833:Microcirculation / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D009399:Nephrons / Q000098:blood supply; D010539:Permeability; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000097:blood / Q000378:metabolism*; D014508:Urea / Q000097:blood / Q000378:metabolism*; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D000804:Angiotensin II; D000001:Calcimycin; D014508:Urea; D012964:Sodium