Nitric oxide affects sarcoplasmic calcium release in skeletal myotubes

In the present study, we used real-time confocal microscopy to examine the effects of two nitric oxide (NO) donors on acetyl-choline (ACh; 10 μM)- and caffeine (10 mM)-induced intracellular calcium concentration ([Ca²⁺]_i) responses in C₂C₁₂ mouse skeletal myotubes. We hypothesized that NO reduces [Ca²⁺]_i in 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⁺]_i level and resulted in a dose-dependent reduction in the amplitude of ACh-induced [Ca²⁺]_i responses (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⁺]_i response. 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.