XB-ART-2313Dev Dyn. May 1, 2005; 233 (1): 142-4.
Pronephric regulation of acid-base balance; coexpression of carbonic anhydrase type 2 and sodium-bicarbonate cotransporter-1 in the late distal segment.
The kidney plays a critical role in regulating the composition of the blood, including pH. The major buffer regulating pH of the blood is bicarbonate. Bicarbonate is freely filtered through the glomerulus and must be recovered from the primary filtrate to maintain appropriate buffering capacity and blood pH. In this report, the expression of carbonic anhydrase type 2 within the late distal segment of pronephroi is described. This expression precisely overlaps that of the sodium-bicarbonate transporter XNBC1. In mammalian kidneys, these two proteins collaborate in the transepithelial recovery of bicarbonate from the kidney filtrate. Coexpression of the genes encoding these proteins in Xenopus embryos indicates that pronephroi use the same recovery system and that this system is largely localized to the late portion of the pronephric distal segment. Not only do the simple pronephroi regulate water and solute balance, they also appear to regulate blood pH in a manner akin to that of the vastly more complex mammalian metanephric kidneys.
PubMed ID: 15712278
Article link: Dev Dyn.
Genes referenced: ca2 slc12a1 slc4a4
Article Images: [+] show captions
|Figure 2. Expression of CA2 in Xenopus laevis embryos. In situ hybridization and fluorescence colorimetric in situ (FCIS) was used to localize CA2 expression in the developing pronephros. Red arrows indicate expression in ventral blood islands, blue arrows light staining in the pronephric proximal tubules, and black arrows strong pronephric late distal segment staining. The numbers in the lower right of each panel indicate developmental stage (Nieuwkoop and Faber, ). A-H: CA2 expression. A: Stage 33 embryo displaying expression in the pronephros and ventral blood islands. B: Enlargement of A. Light staining is observed in the proximal tubules and darker staining in the late distal segment. C,D: Stage 35 embryo. E,F: Stage 37 embryo. G,H: Stage 39 embryo. I: FCIS showing CA2 expression with a sodium-potassium ATPase counterstain. Pink indicates weak overlap, orange no overlap. Strong CA2 expression appears blue. J: FCIS combining CA2 staining with a NKCC2 counterstain. There is no overlap in the early distal segment, which is orange. K: FCIS showing XNBC1 (blue) with a sodium potassium ATPase counterstain. Localization of XNBC1 is indistinguishable from that of CA2 shown in I. (K is reproduced from Zhou and Vize, Dev Biol 271:322-338, and is copyrighted by Elsevier 2004.)|
|Xenopus carbonic anhydrase 2, ca2, expression in stage 39 tadpole by in situ hybridization|