Vasopressin-independent renal urinary concentration: increased rBSC1 and enhanced countercurrent multiplication.
BACKGROUND
A close association between the expression of the sodium transporter, rat bumetanide sensitive cotransporter (rBSC), in thick ascending limb of Henle and urinary concentration has been reported. However, direct evidence for this association and the mechanism of rBSC1 expression are still to be elucidated.


METHODS
Brattleboro (BB) rats weighing approximately 200 g were dehydrated by water restriction for 4 hours, which induced around a 5% body weight reduction. Although plasma arginine vasopressin (AVP) was undetectable even after the water restriction, BB rats concentrated urine from 182 +/- 23 (mean +/- SD) at baseline to 404 +/- 65 mOsm/kg. H2O.


RESULTS
Urinary volume was reduced from 5.8 +/- 1.8 to 1.4 +/- 0.6 mL/h. This treatment significantly increased sodium and urea accumulation in the renal medulla and reduced urinary sodium excretion. rBSC1 signals for both mRNA and protein were increased in dehydrated rats, although aquaporin type 2 (AQP2) expression was not enhanced in dehydrated BB rats. Subcutaneous infusion of desmopressin acetate (DDAVP) intensified rBSC1 signals of BB rats more than those in dehydrated condition.


CONCLUSIONS
Dehydration increased rBSC1 expression and enhanced countercurrent multiplication even in AVP deficiency. These results supply strong evidence for the association between rBSC1 expression and urinary concentration, and indicate the presence of an AVP-independent mechanism for urine concentration.
Michimata
Mari
M
Department of Molecular Medicine and Gene Transfer Research, Tohoku University School of Medicine, Sendai, Japan.
Mizukami
Kazuhiko
K
Suzuki
Michiko
M
Kazama
Itsuro
I
Nakamura
Yohsuke
Y
Suzuki
Katsuya
K
Yanagisawa
Teruyuki
T
Imai
Yutaka
Y
Sasaki
Sei
S
Matsubara
Mitsunobu
M
D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins / Q000378:metabolism; D001769:Blood / Q000378:metabolism; D004231:Diuresis; D004573:Electrolytes / Q000378:metabolism; D007671:Kidney Concentrating Ability / Q000502:physiology*; D007679:Kidney Medulla / Q000378:metabolism; D051381:Rats; D011910:Rats, Brattleboro; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*; D064466:Solute Carrier Family 12, Member 1; D014508:Urea / Q000378:metabolism; D014556:Urine / Q000737:chemistry; D014667:Vasopressins / Q000502:physiology*
C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D004573:Electrolytes; C578716:Slc12a1 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D014667:Vasopressins; D014508:Urea