Figure 2. SNAP treatment decreases twitch size in an EDL fibre.

Twitch (single pulse) and tetanic responses (50 Hz, 20 pulses) elicited in a skinned EDL fibre before and after exposure to NO^• donor SNAP (2 mm for 2 min), and also after treatment with DTT. Stimulus timing shown under force trace. Responses elicited in standard K-HDTA solution. Lowering free [Mg²⁺] from 1 mm to 15 μm triggered a large and prolonged release of Ca²⁺ from SR. Maximum Ca²⁺-activated force (‘max’) measured at pCa 4.5 (and 1 mm free Mg²⁺). Time scale: 1 s for twitches and tetani, and 10 s for 15 μm free Mg²⁺ and max responses.