TY - JOUR
T1 - Bicarbonate reabsorption and NHE-3 expression
T2 - Abundance and activity are increased in Henle's loop of remnant rats
AU - Capasso, Giovambattista
AU - Rizzo, Maria
AU - Pica, Angelo
AU - Di Maio, Francesco S.
AU - Moe, Orson W.
AU - Alpern, Robert J.
AU - De Santo, Natale G.
N1 - Funding Information:
This work was supported by a Grant from MURST (PRIN 1998) and by Regione Campania (Legge 41) to G. Capasso. The S3226 substance was a kind gift from Hoechst. M.R. and A.P. were supported by the Ph.D. program in Nephrological Science. O.M. was supported by NIH grants [RO1-DK48482 and RO1-DK54396] and by the Department of Veterans Affairs Research. R.A. was supported by NIH grant R37-DK-39298. Part of this work was presented at the Philadelphia Meeting of the American Society of Nephrology and published in abstract form (J Am Soc Nephrol 10:A0007, 1999).
PY - 2002
Y1 - 2002
N2 - Background. The bulk of bicarbonate reabsorption along the loop of Henle (LOH) is localized at the level of the thick ascending limb (TAL) and is mainly dependent on the presence of luminal Na+-H+ exchanger (NHE-3). We investigated whether the reduction of renal mass is associated with alterations in LOH bicarbonate transport coupled to changes in NHE-3 gene expression and in vivo activity. Methods. Sham-operated and remnant rats (4/6 nephrectomy) were studied 15 days after the surgery. To measure net bicarbonate reabsorption (JHCO3-) superficial loops were perfused by in vivo micropuncture. Perfusate was an end-like proximal solution containing 3H-methoxy-inulin. NHE-3 gene expression was quantified by competitive PCR using an internal standard of cDNA that differed from the wild-type NHE-3 by a deletion of 76 bp. Western blot experiments were performed on TAL suspension using anti-NHE-3 antibodies. Results. At various LOH bicarbonate loads, JHCO3- was constantly larger in remnant rats as compared to sham-operated animals. NHE-3 mRNA abundance was estimated to be 0.339 ± 0.031 attomoles (amol)/ng-1 total RNA in sham-operated (N = 5) and it increased to 0.465 ± 0.023 in remnant rats (N = 5, P < 0.01). Western blot experiments showed a significant increase of NHE-3 protein abundance in TAL of remnant rats as compared to sham-operated animals. Finally, by means of a specific NHE-3 inhibitor, S-3226, in vivo micro perfusion experiments demonstrated that NHE-3 in vivo activity along the LOH was substantially increased in remnant rats in addition to the non-NHE-3 bicarbonate transport. Conclusions. These data indicate that the reduction of renal mass increases mRNA, protein abundance and in vivo activity of NHE-3 along the TAL. This may explain, at least in part, the augmented transepithelial bicarbonate transport along the LOH. Such an effect will counterbalance the increased glomerular bicarbonate load, thus preventing urinary bicarbonate loss and mitigating the ensuing metabolic acidosis.
AB - Background. The bulk of bicarbonate reabsorption along the loop of Henle (LOH) is localized at the level of the thick ascending limb (TAL) and is mainly dependent on the presence of luminal Na+-H+ exchanger (NHE-3). We investigated whether the reduction of renal mass is associated with alterations in LOH bicarbonate transport coupled to changes in NHE-3 gene expression and in vivo activity. Methods. Sham-operated and remnant rats (4/6 nephrectomy) were studied 15 days after the surgery. To measure net bicarbonate reabsorption (JHCO3-) superficial loops were perfused by in vivo micropuncture. Perfusate was an end-like proximal solution containing 3H-methoxy-inulin. NHE-3 gene expression was quantified by competitive PCR using an internal standard of cDNA that differed from the wild-type NHE-3 by a deletion of 76 bp. Western blot experiments were performed on TAL suspension using anti-NHE-3 antibodies. Results. At various LOH bicarbonate loads, JHCO3- was constantly larger in remnant rats as compared to sham-operated animals. NHE-3 mRNA abundance was estimated to be 0.339 ± 0.031 attomoles (amol)/ng-1 total RNA in sham-operated (N = 5) and it increased to 0.465 ± 0.023 in remnant rats (N = 5, P < 0.01). Western blot experiments showed a significant increase of NHE-3 protein abundance in TAL of remnant rats as compared to sham-operated animals. Finally, by means of a specific NHE-3 inhibitor, S-3226, in vivo micro perfusion experiments demonstrated that NHE-3 in vivo activity along the LOH was substantially increased in remnant rats in addition to the non-NHE-3 bicarbonate transport. Conclusions. These data indicate that the reduction of renal mass increases mRNA, protein abundance and in vivo activity of NHE-3 along the TAL. This may explain, at least in part, the augmented transepithelial bicarbonate transport along the LOH. Such an effect will counterbalance the increased glomerular bicarbonate load, thus preventing urinary bicarbonate loss and mitigating the ensuing metabolic acidosis.
KW - Acid-base balance
KW - Loop of Henle
KW - Metabolic alkalosis
KW - Micropuncture
KW - RT-PCR
KW - Sodium-hydrogen exchanger
KW - Urinary bicarbonate loss
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U2 - 10.1046/j.1523-1755.2002.00681.x
DO - 10.1046/j.1523-1755.2002.00681.x
M3 - Article
C2 - 12427137
AN - SCOPUS:0036433431
SN - 0085-2538
VL - 62
SP - 2126
EP - 2135
JO - Kidney international
JF - Kidney international
IS - 6
ER -