Effects of cytochalasins on the mechanical and membrane responses in the isolated longitudinal myometrium of pregnant rat with reference to the EGTA-resistant contraction.

Effects of cytochalasins B and D (CB, CD) were examined for the contractions of the longitudinal myometrium of pregnant rat exposed to Krebs solution, 40 mM K Krebs, and Ca-free (40 mM K) solution containing 5 mM Mg. The Ca-free contraction was evoked by applying 3 mM ATP. Application of CB caused a prompt inhibition of the contractions: 3 microM CB depressed the twitch contraction generated in Krebs solution by 12%, the K-contracture by 6%, and the ATP-induced contraction in the Ca-free solution by 59%. CD (3 microM) depressed the K-contracture by 31%, and the ATP-induced contraction in the Ca-free solution by 81%. CB and CD in 3 microM hyperpolarized the membrane and depressed the generation of action potential. From the above results, it was discussed that depressant effects of cytochalasins on twitch contractions in Krebs solution are at least in part due to the depression of membrane excitability, whereas contractions evoked in high K solutions are depressed by cytochalasins due to their effects on cytoskeleton.