Figure 1.

Effects of xestospongin-C (Xest-C, 3 and 10 μM) on transient contractions due to Ca²⁺ release from the sarcoplasmic reticulum in α-toxin-skinned muscle fibres. Prior to the experiment the muscle had been conditioned by adding 20 mM caffeine. We then induced contractions with IP₃ (30 μM), GTP (100 μM)+carbachol (10 μM) and caffeine (3 mM) twice to demonstrate the reproducibility of these responses. (A) Typical tracing of the effects of 3 μM xestospongin-C on transient contraction induced by 30 μM IP₃ in Ca²⁺-free solution. (B) Typical tracing of the effects of 3 μM xestospongin-C on a transient contraction induced by 10 μM carbachol in the presence of 100 μM GTP. (C) Typical tracing of the effects of 3 μM xestospongin-C on a transient contraction induced by 3 mM caffeine. (D) The area of force oscillations during a 15 min period was used for quantitative assessment of the effects of caffeine, carbachol and IP₃, and the summarized data of (A), (B) and (C) is shown (n=6 each). **P < 0.01 vs control. 100% represents the first control response before the addition of xestospongin-C.