A purinergic signal transduction pathway in mammalian skeletal muscle cells in culture.

The effects of adenosine 5'-triphosphate (ATP) on human and mouse skeletal muscle fibres in primary culture were investigated. ATP-evoked changes in intracellular calcium concentration ([Ca(2+)](i)) were measured and compared with those induced by agonists of the nicotinic acetylcholine (Ach)- and P2X purinoreceptors. While ATP was effective on both myoblasts and multi-nucleated myotubes in the micromolar range, Ach failed to induce any change in [Ca(2+)](i) at early stages of development. In contrast, myofibres with peripheral nuclei showed little response to ATP but responded to Ach with a large change in [Ca(2+)](i). The responsiveness of the myotubes to Ach paralleled that to potassium. The removal of external calcium abolished the response to ATP. P2X receptor agonists mimicked the response to ATP with the order of potency being ATP>2',3'- O-(4-benzoyl)-benzoyl-ATP>beta,gamma-methylene-ATP>alpha,beta-methylene-ATP. Under voltage-clamp conditions ATP induced an inward current that showed little inactivation. These results are consistent with the existence of P2X receptor-mediated signal transduction pathway in cultured mammalian skeletal muscle cells.