NaCl-dependent expression of amiloride-blockable Na⁺ channel in Xenopus oocytes

RNA was isolated from chicken lower intestine (both colon and coprodeum) and injected into Xenopus oocytes. ²²Na⁺ fluxes measured after 1-4 days demonstrated the induction of an amiloride-blockable pathway. The Na⁺ transporter expressed by the exogenous RNA had a high affinity to amiloride (inhibitory constant < 0.1 μM), but was insensitive to ethylisopropyl amiloride, i.e., it is likely to be the apical Na⁺ channel. Functional channels were readily expressed in oocytes injected with RNA derived from chickens fed a low-NaCl diet. On the other hand, no channel activity was detected in oocytes injected with RNA isolated from chickens fed a high-NaCl diet. Thus the previously reported regulation of transport by the dietary NaCl intake involves modulations in the level of mRNA that codes either for the Na⁺ channel or a posttranscriptional regulator of the channel.