Machiels, Herwin A.

In the present study, we used real-time confocal microscopy to examine the effects of two nitric oxide (NO) donors on acetylcholine (ACh; 10 μM)- and caffeine (10 mM)-induced intracellular calcium concentration ([Ca2+]i) responses in C2C12mouse skeletal myotubes. We hypothesized that NO reduces [Ca2+]iin activated skeletal myotubes through oxidation of thiols associated with the sarcoplasmic reticulum Ca2+-release channel. Exposure to diethylamine NONOate (DEA-NO) reversibly increased resting [Ca2+]ilevel and resulted in a dose-dependent reduction in the amplitude of ACh-induced [Ca2+]iresponses (25 ± 7% reduction with 10 μM DEA-NO and 78 ± 14% reduction with 100 μM DEA-NO). These effects of DEA-NO were partly reversible after subsequent exposure to dithiothreitol (10 mM). Preexposure to DEA-NO (1, 10, and 50 μM) also reduced the amplitude of the caffeine-induced [Ca2+]iresponse. Similar data were obtained by using the chemically distinct NO donor S-nitroso- N-acetyl-penicillamine (100 μM). These results indicate that NO reduces sarcoplasmic reticulum Ca2+release in skeletal myotubes, probably by a modification of hyperreactive thiols present on the ryanodine receptor channel.