Figure 3. Effects of DTDP and GSH on twitch, tetani and t-system excitability.

A, twitch and tetanic (50 Hz) responses in an EDL fibre elicited before treatment (control) and after successive treatments with DTDP (100 μm, 30 s), GSH (5 mm, 2 min) and DTT (10 mm, 2 min). Twitch force was decreased by oxidation with DTDP and greatly potentiated by glutathionylation with GSH. These changes were explicable by alterations in Ca²⁺ sensitivity of the contractile apparatus, and were fully reversed by DTT treatment. B, twitch response to single electrical pulses (‘s’) or to pairs of pulses with interpulse intervals of 1–20 ms (shown above responses), before and after each treatment; twitch force increased substantially with interpulse intervals of 4 ms or longer in all cases, indicative of the repriming period required for the second pulse to also trigger an AP. C, twitch responses from B, all expressed relative to the response to a single pulse under control conditions.