Fig. 5. The contribution to apical membrane NHE3-EGFP recovery after photobleaching of intracellular NHE3-EGFP was negligible when non-JN NHE3 was studied but was significant in the above-JN region. Fluorescence recovery was studied after 30 minutes exposure at 4°C to the water-soluble cross-linking reagent, BS³ (10 mM). NHE3-EGFP recovery was performed on the intracellular JN (cyto-JN) (A), apical plasma membrane above-JN (B) and non-JN (C) domains. The mobile fractions (D) and diffusion coefficients (E) of the NHE3-EGFP domains were determined by FRAP. Data shown are mean±s.e.m. * P values compared with cyto-JN are shown (unpaired t-test). n=7 for cyto-JN and non-JN; n=6 for above-JN.