STUDY ON CARBONIC ANHYDRASE IN RENAL TUBULE EPITHELIA

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Carbonic anhydrase IV (Ca IV) is a key enzyme in the bicarbonate reabsorption in proximal renal tubule. CA IV deficiency is possibly causative for some forms of proximal renal tubular acidosis. We investigated carbonic anhydrase in the patient suffered with persistent, pure proximal renal tubular acidosis.We studied carbonic anhydrase II (CA II) and IV in urinary membrane and soluble fractions in the patient and normal controls. Membrane-associated CA II of the patient was similar to that of normal controls in the immunochemical detection and activity measurement. Immunochemically detected membrane-associated CA IV was identical in the size in both the patient and normal controls, but much less in the band intensity in the patient than in normal controls. Soluble CA IV was much increased in the patient. These results suggested that the anchoring mechanism of CA IV to membrane may be abnormal and causative for proximal renal tubular acidosis in the patient. Alkalinephosphatase in urinary membrane fraction, which anchored to membrane via glycosyl-phosphatidylinositol as same as CA IV,was simultaneously studied and was normal. We speculated that subtle mutation in CA IV gene especially in C-terminal domain might be responsible for the disease.We amplified the 7 exons in CA IV gene with 7 sets of PCR primers constructed a ccording with the intronic sequence, and sequenced them using the PCR primer as sequence primer. No mutation was detected in the exon-intron boundaries and exons.We concluded that the mutation in CA IV was unlikely in the patient. The cause of the patient with persistent, pure proximal renal tublar acidosis is still remained to be elucidated.