Background: 

Intestinal NHE3 is scaffolded and differentially regulated by Na⁺/H⁺ exchanger regulatory factor (NHERF) PDZ-adaptors. NHE3 partially resides in membrane rafts of the brush border membrane (BBM). Aim: To investigate if there is a cross-talk between NHERFs and membrane rafts, specifically if NHERFs associate differentially with the raft and non-raft fractions of NHE3, and whether they influence the function and distribution of NHE3 in these microdomains.

Methods and Results: 

Murine BBM was detergent-solubilised and membrane rafts were isolated by density gradient flotation. NHE3 was partially, NHERF2 strongly and NHERF1 weakly raft-associated, and NHERF3 exclusively in the non-raft fraction demonstrating that NHERF proteins differentially associate with the raft and non-raft pools of NHE3. NHE3 raft association was NHERF2-dependent as in the absence of NHERF2, raft-associated NHE3 was virtually absent. Using a mouse model for increased membrane glycosphingolipid ratio, increased NHE3-dependent small intestinal fluid absorption in vivo, as well as overall NHE3 in rafts was observed; suggesting a positive correlation between NHE3 function and raft association.

Conclusions: 

The data suggests that PDZ-scaffolding proteins are involved in the retention of membrane proteins within raft platforms. Moreover, the differential regulation of NHE3 by NHERF PDZ-adapters might be the result of specific NHERFs interacting with physically separated pools of NHE3.