EXPRESSION OF CARBONIC-ANHYDRASE-IV MESSENGER-RNA IN RABBIT KIDNEY - STIMULATION BY METABOLIC-ACIDOSIS

The renal carbonic anhydrases, CA II (cytosolic) and CA TV (membrane b ound), are believed to facilitate renal acid secretion. We have recent ly shown that renal cortical sodium dodecyl sulfate (SDS)-resistant hy dratase (presumably CA IV) activity was stimulated 241% during chronic metabolic acidosis (CMA). In the present study, we examined the expre ssion and regulation of CA IV mRNA in kidneys from control and acidoti c rabbits. To obtain a CA IV probe, we reverse transcribed rabbit kidn ey total RNA and amplified a similar to 780-base pair (bp) DNA product using primers derived from the human CA IV sequence. Using this produ ct, we screened one-half of a kidney cortex cDNA library and sequenced a 1,194-bp cDNA, which contained the entire open-reading frame of rab bit CA. IV. The cDNA was 78% identical to human and 71% to rat CA IV. The deduced amino acid sequence projected an active zinc binding site and two glycosylation sites. Northern analysis yielded a single transc ript of similar to 1,600 bp in size expressed more abundantly in corte x and inner medulla than in outer medulla. CA IV mRNA was also express ed abundantly in lung but not in liver or spleen. The high abundance o f CA IV mRNA in inner medulla was localized by in situ hybridization t o medullary collecting duct cells. Rabbits exposed to CMA showed signi ficant upregulation of CA IV mRNA expression in kidney cortex and oute r medulla. Despite a numerical increase, excessive variability preclud ed statistical significance in the inner medulla. Thus CA TV mRNA was expressed abundantly in kidney and stimulated by CMA, similar to what has been previously observed for SDS-resistant hydratase (presumed CA IV) activity. It is likely that the regulation of CA IV mRNA and activ ity is relevant to the kidney's adaptation to CMA.