NBC1 mediates 80% of bicarbonate reabsorption by the kidney but the molecular determinants for activity, targeting and cell membrane stability are poorly understood. We generated truncation mutants involving the entire amino (N424) or the entire carboxyl (C92) terminus and examined the effects of these truncations on targeting, cell membrane stability and NBC1 activity. N424 and C92 targeted to the plasma membrane of HEK293 cells or to the basolateral membrane of OK cells at 24 hr but did not display NBC1 activity. Unlike the NBC1 wild type (WT) and the N424, the C92 expression was significantly decreased in the basolateral membrane at 48 hr and yet the total C92 expression in the cell was constant. We found that decreased C92 expression in the basolateral membrane was due to increased endocytosis and mistargeting to the apical membrane. Increased endocytosis was prevented when both N424 and C92 were cotransfected together and more stable expression of C92 was observed. Immunoprecipitation studies using NBC1 antibody specific for the COOH epitope were able to detect the carboxyl truncated NBC1 when probed with NH2 epitope specific antibody or vice versa. Similar findings were observed with Ni-NTA pull down assay. Cotransfection of both mutants partially restored NBC1 activity. In summary, NBC1 targets to the basolateral membrane of OK cells by a default mechanism and the COOH terminus plays a role on NBC1 stability in the basolateral membrane.