The effect of rapamycin on single ENaC channel activity and phosphorylation in A6 cells

• Published in: American Journal of Physiology: Cell Physiology 2000-07, Vol.279 (1), p.C81-C88
• Main Authors: Yue, Gang, Edinger, Robert S, Bao, Hui-Fang, Johnson, John P, Eaton, Douglas C
• Format: Article
• Language: English
• Subjects: Drug Interactions; Enzyme Inhibitors - pharmacology; Epithelial Sodium Channels; Immunophilins - genetics; Immunosuppressive Agents - pharmacology; Indoles - pharmacology; Maleimides - pharmacology; Patch-Clamp Techniques; Phosphorylation - drug effects; Protein Kinase C - antagonists & inhibitors; Sirolimus - pharmacology; Sodium Channels - drug effects; Sodium Channels - metabolism; Sodium Channels - physiology; Tacrolimus - pharmacology; Tacrolimus Binding Proteins; Tetradecanoylphorbol Acetate - pharmacology
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.2000.279.1.c81

1  Center for Cell and Molecular Signaling and 2  Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322; and 3  Renal Electrolyte Division, The University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213-2550 Rapamycin and FK-506 are immunosuppressive drugs that bind a ubiquitous immunophilin, FKBP12, but immunosuppressive mechanisms and side effects appear to be different. Rapamycin binds renal FKBP12 to change renal transport. We used cell-attached patch clamp to examine rapamycin's effect on Na + channels in A6 cells. Channel NP o was 0.5 ± 0.08 ( n  = 6) during the first 5 min but fell close to zero after 20 min. Application of 1 µM rapamycin reactivated Na + channels ( NP o  = 0.47 ± 0.1; n =6), but 1 µM FK-506 did not. Also, GF-109203X, a protein kinase C (PKC) inhibitor, mimicked the rapamycin-induced reactivation in a nonadditive manner. However, rapamycin did not reactivate Na + channels if cells were exposed to 1 µM FK-506 before rapamycin. In PKC assays, rapamycin was as effective as the PKC inhibitor; however, epithelial Na + channel (ENaC) phosphorylation was low under baseline conditions and was not altered by PKC inhibitors or activators. These results suggest that rapamycin activates Na + channels by binding FKBP12 and inhibiting PKC, and, in renal cells, despite binding the same immunophilin, rapamycin and FK-506 activate different intracellular signaling pathways. epithelial sodium channel; amiloride-sensitive sodium channels; protein kinase C; single channels