The Effect of Dynasore Upon the Negative Interaction Between ENaC and CFTR Channels in Xenopus laevis Oocytes

Shroom is a family of related proteins linked to the actin cytoskeleton, and one of them, xShroom1, is constitutively expressed in Xenopus laevis oocytes which is required for the expression of the epithelial sodium channel (ENaC). On the other hand, ENaC and the cystic fibrosis transmembrane regulator (CFTR) are co-expressed in many types of cells with a negative or positive interaction depending on the studied tissues. Here, we measured the amiloride-sensitive ENaC currents (INa_amil) and CFTR currents (I_CFTR) with voltage clamp techniques in oocytes co-injected with ENaC and/or CFTR and xShroom1 antisense oligonucleotides. The objective was to study the mechanism of regulation of ENaC by CFTR when xShroom1 was suppressed and the endocytic traffic of CFTR was blocked. CFTR activation had a measurable negative effect on ENaC and this activation resulted in a greater inhibition of INa_amil than with xShroom1 antisense alone. Our results with Dynasore, a drug that acts as an inhibitor of endocytic pathways, suggest that the changes in INa_amil by xShroom1 downregulation were probably due to an increment in channel endocytosis. An opposite effect was observed when I_CFTR was measured. Thus, when xShroom1 was downregulated, the I_CFTR was larger than in the control experiments and this effect is not observed with Dynasore. A speculative explanation could be that xShroom1 exerts a dual effect on the endocytic traffic of ENaC and CFTR and these actions were canceled with Dynasore. In the presence of Dynasore, no difference in either INa_amil or I_CFTR was observed when xShroom1 was downregulated.