Effects of dantrolene and its derivatives on Ca2+ release from the sarcoplasmic reticulum of mouse skeletal muscle fibres

1 We analysed the effect of dantrolene (Dan) and five newly synthesized derivatives (GIFs) on Ca2+ release from the sarcoplasmic reticulum (SR) of mouse skeletal muscle. 2 In intact muscles, GIF-0185 reduced the size of twitch contraction induced by electrical stimulation to the same extent as Dan. GIF-0082, an azido-functionalized Dan derivative, also inhibited twitch contraction, although the extent of inhibition was less than that of Dan and of GIF-0185. 3 In skinned fibres, Dan inhibited Ca2+-induced Ca2+ release (CICR) under Mg2+-free conditions at room temperature. In contrast, GIF-0082 and GIF-0185 showed no inhibitory effect on CICR under the same conditions. 4 Dan-induced inhibition of CICR was not affected by the presence of GIF-0082, whereas it was diminished in the presence of GIF-0185. 5 GIF-0082 and GIF-0185 significantly inhibited clofibric acid (Clof)-induced Ca2+ release, as did Dan. 6 Several Dan derivatives other than GIF-0082 and GIF-0185 showed an inhibitory effect on twitch tension but not on the CICR mechanism. All of these derivatives inhibited Clof-induced Ca2+ release. 7 The magnitudes of inhibition of Clof-induced Ca2+ release by all Dan derivatives were well correlated with those of twitch inhibition. This supports the notion that the mode of Clof-induced opening of the RyR-Ca2+ release channel may be similar to that of physiological Ca2+ release (PCR). 8 These results indicate that the difference in opening modes of the RyR-Ca2+ release channel is recognized by certain Dan derivatives.