The ATP-operated P2X4 receptor is localized in the T-tubule membranes of skeletal muscle

The aim of the study was to investigated in skeletal muscle the expression, localization and possible function of P2X4 receptor, an extracellular ATP-operated channel mainly permeable to Ca2+. By RT-PCR and Western blot analysis we have demonstrated that P2X4 is expressed in several rat tissues, including skeletal muscle. A specific antibody detected a protein band of about 60 kDa whose level was higher in slow-than in fast-twitch muscles. P2X4 receptor is highly glycosylated because digestion with N-glycosidase F reduced the mass of the 60-kDa protein to about 45 kDa. Confocal immunofluorescence in longitudinal sections revealed that P2X4 receptor is transversally distributed and co-localized with the DHP receptor. This finding indicates that P2X4 decorates T-tubule membranes and raises the possibility that this ATP-gated cation channel may contribute to ECcoupling of skeletal muscle. In vitro experiments showed that stimulation of muscle fibers evokes the release of ATP, while tension recordings evidenced an ATP-dependent potentiation of contractility, particularly in fast-twitch muscles. The financial support of TELETHON ITALY (grants n. 1286) is gratefully acknowledged.