CLONING, RENAL DISTRIBUTION, AND REGULATION OF THE RAT NA-HCO3- COTRANSPORTER()

We recently reported the cloning and expression of a human kidney Na+- HCO3- co-transporter (NBC-1) (C. E. Burnham, H. Amlal, Z. Wang, G. E. Shull, and M. Soleimani. J. Biol. Chem. 272: 19111-19114, 1997). To ex pedite in vivo experimentation, we now report the cDNA sequence of rat kidney NBC-1. In addition, we describe both the organ and nephron seg ment distributions and the regulation of NBC-1 mRNA under three models of pH stress: chloride-depletion alkalosis (CDA), metabolic acidosis, and bicarbonate loading. Rat NBC-1 cDNA encodes an open reading frame of 1,035 amino acids, with 96 and 87% identity to human and salamande r NBC-1, respectively. Rat NBC-1 mRNA is expressed at high levels in k idney and brain, with lower levels in colon, stomach, and heart. None appears in liver. In the kidney, NBC-1 is expressed mainly in the prox imal tubule, with traces found in medullary thick. ascending limb and papilla. HCO3- loading decreased NBC-1 mRNA. levels, which were unchan ged either by metabolic acidosis or by CDA.