The mechanisms underlying regulatory interactions of the cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial Na+ channel (ENaC) in Xenopus oocytes are controversial. CFTR's first nucleotide binding domain (NBD-1) may be important in these interactions, as mutations within NBD-1 impair these functional interactions. We hypothesized that an abnormal CFTR containing a non-NBD-1 mutation that is able to transport chloride would retain regulatory interactions with murine ENaC (mENaC). We tested this hypothesis for I148T-CFTR where the mutation is located in CFTR's first intracellular loop. I148T-CFTR has been associated with a severe CF phenotype, perhaps due to defects in regulation of bicarbonate transport, but transports chloride similar to wild type CFTR in model systems (Choi, JY, et al., Nature, 410:94, 2001). cRNA's encoding -mENaC and I148T-CFTR were injected separately or together into Xenopus oocytes. mENaC and CFTR functional expression were assessed by two-electrode voltage clamp. mENaC whole oocyte expression was determined by immunoblot, and surface expression quantitated by surface biotinylation. Injection of I148T-CFTR cRNA alone yielded high levels of CFTR functional expression. In co-injected oocytes, mENaC functional and surface expression was not altered by activation of I148T-CFTR with forskolin/isobutylmethylxanthine (IBMX). Furthermore, the CFTR potentiator genistein both enhanced the functional expression of I148T-CFTR and restored regulation of mENaC surface expression by activated I148T-CFTR. These data suggest that the ability to transport chloride is not a critical determinant of regulation of mENaC by activated CFTR in Xenopus oocytes, and provide further evidence that I148T-CFTR is dysfunctional despite maintaining the ability to transport chloride.