[Changes in the force-pCa characteristics of the striated muscles of the skate after treatment with phalloidin].

The pCa/tension relationship of glycerinated skate thoracic fin muscle was found to fit well in the Hill equation. Phalloidin has been shown to decrease calcium sensitivity (shift of pK to the lower pCa by 0.27 +/- 0.08), tension at saturated pCa by 22 +/- 5%, and Hill coefficient by 0.37 +/- 0.21. As F-actin structural motility is restricted by phalloidin, these results are in agreement with the idea of participation of F-actin conformational changes in its switching by calcium ions and in ensuring cooperativity of this process.