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Abstract:
The effect of phalloidin (Ph) and some of its derivatives on isometric tension and spectrum of mechanical relaxation times of single fibres was under investigation. It was shown that Ph had a great effect only at low levels of Ca2+-activation, evoking multi-phase changes of isometric tension and a sharp rise of the rate constant of delayed tension development up to value close to that for control fibres at high [Ca2+]. As to their efficiency to change Ca2+-sensitive parameters of the fibres, phallotoxins can be arranged as follows: Ph approximately equal to Ph-sulfone greater than Ph-sulfoxide B approximately equal to dethio-Ph greater than Ph-sulfoxide A greater than or equal to seco-Ph. There is a qualitative correlation of this sequence with the actin stabilising properties for all these substances with the exception of dethio-Ph. These findings are discussed from the viewpoint of two different "on" actin states, only one of them being Ph-sensitive.
