Carbonic anhydrase II and IV mRNA in rabbit nephron segments: stimulation during metabolic acidosis

Abstract

Carbonic anhydrase (CA) facilitates renal bicarbonate reabsorption and acid excretion. Cytosolic CA II catalyzes the buffering of intracellular hydroxyl ions by CO2, whereas membrane-bound CA IV catalyzes the dehydration of carbonic acid generated from the secretion of protons. Although CA II and IV are expressed in rabbit kidney, it is not entirely clear which segments express which isoforms. It was the purpose of this study to characterize the expression of CA II and CA IV mRNAs by specific segments of the nephron using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and to determine the effect of chronic metabolic acidosis on CA expression by those segments. Individual nephron segments (usually 1–2 mm) were isolated by microdissection and subjected to RT-PCR. Amplification was performed simultaneously for CA IV, CA II, and malate dehydrogenase (MDH), a housekeeping gene. The intensities of the PCR products were quantitated by densitometry. CA IV mRNA was expressed by S1 and S2 proximal tubules and by outer medullary collecting duct from inner stripe (OMCDi) and outer stripe and initial inner medullary collecting duct (IMCDi). CA II mRNA was expressed by S1, S2, and S3 proximal tubules, thin descending limb, connecting segment (CNT), and all collecting duct segments. Acid loading induced CA IV mRNA expression in S1 and S2 proximal tubules and in OMCDi and IMCDi. CA II mRNA was induced by acidosis in all three proximal segments and nearly all distal segments beginning with CNT. No upregulation of MDH mRNA expression occurred. These adaptive increases in CA II and IV mRNAs are potentially important in the kidney’s adaptation to chronic metabolic acidosis.

Kidney collecting duct acid-base “regulon”

“…Loss-of-function mutations of the cytoplasmic Car2 induce distal acidosis (36), demonstrating its nonredundant role in collecting duct acid-base transport. In contrast, the apical ecto-isoform has not been characterized yet, even though Car4 is a candidate (48). Present results support the role of Car2 in bicarbonate reabsorption, since it is expressed at a high level in the collecting duct and is induced concomitantly with HATPase during acidosis.…”

Carbonic anhydrase and acid–base regulation in fish

“…Lungfish, while exhibiting a significant renal component to the compensation of metabolic acidosis or alkalosis, showed no changes in renal CA mRNA expression (Gilmour et al, 2007b). The absence of any change in renal mRNA levels for cytosolic CA during metabolic acidosis is surprising given that similar treatment in mammals causes a marked increased in the expression of CA II (Tsuruoka et al, 1998). Several explanations can be offered for the lack of an effect in the lungfish: the sampling time may have been inappropriate thus preventing detection of a transient change in mRNA expression; or CA was being modified post-translationally.…”

Altered Gene Expression Profiles in the Brain, Kidney, and Lung of One-Month-Old Cloned Pigs

“…Functional annotation and intensive literature mining revealed the clinical relevance of differentially expressed genes in organs of the cloned pigs. Six genes dysregulated in the kidney of cloned pigs were identified to have potential role in diabetic nephropathy: CA2 catalyzes the buffering of intracellular hydroxyl ions by CO 2 in S1, S2, and S3 proximal segments of the nephrons, and renal adaptation to the metabolic acidosis potentially increases its expression (Tsuruoka et al, 1998). The strong induction of renal G6PC during starvation has been suggested to be responsible for glucose production in the kidney during long-term fasting (Simonnet, 1999).…”