Carbonic anhydrase II mRNA is induced in rabbit kidney cortex during chronic metabolic acidosis

Carbonic anhydrase II (CA II), the predominant isoform of carbonic anhydrase in the kidney, is believed to be localized primarily in the cytoplasm of proximal tubule and collecting duct intercalated cells. Carbonic anhydrase facilitates H⁺ secretion by catalyzing the formation of HCO₃^- from OH^- in the presence of CO₂. We have shown that renal cortical CA II activity is stimulated during 4-6 days of chronic metabolic acidosis [L. P. Brion, B. J. Zavilowitz, O. Rosen, and G. J. Schwartz. Am. J. Physiol. 261 (Regulatory Integrative Comp. Physiol. 30): R1204-R1213, 1991]. The purpose of these studies was to examine under similar conditions the regulation of CA II mRNA. We obtained a major portion of the rabbit CA II cDNA by reverse transcription of total RNA from rabbit kidney followed by amplification using oligonucleotide primers prepared from conserved areas in the coding regions of human, mouse, and chick CAII cDNAs in a polymerase chain reaction (RT-PCR). The 696-bp RT-PCR product was sequenced and found to be 71-86% homologous to CA II cDNAs from the other three species. The deduced amino acid sequence agreed closely (>97%) with a previous Edman analysis of rabbit erythrocyte CA II. Northern analysis showed expression of a ∼ 1.4 kb RNA, with cortex > outer medulla > inner medulla. Steady-state mRNA expression from kidney cortex of acid-treated rabbits was about twice that from controls, when normalized to the expression of β-actin or malate dehydrogenase. The stimulation of CA II mRNA was greater after 3 days than after 5-6 days of acid treatment. Thus, during chronic metabolic acidosis, there is an induction of CA II mRNA, which precedes the increase in activity, indicating a possible role for this enzyme in the renal adaptation to this pathological state.