phalloidine and Muscle-Weakness

Secophalloidin (SPH) is known to cause in cardiac myofibrils force without Ca(2+) (half-maximal effect approximately 2 mM) followed by irreversible loss of Ca(2+)-activated force. At maximal Ca(2+) activation, SPH increases force (half-maximal effect < 0.1 mM). We found that SPH at low concentration (0.5 mM) did not cause either force activation or force loss at pCa 8.7, but both of these effects did occur when force was activated by Ca(2+). The force loss was prevented when SPH was applied during rigor or in the presence of 2,3-butanedione monoxime (85 mM). Furthermore, studying muscle in which the force was previously reduced by SPH (up to 50%) did not reveal significant changes in Ca(2+) sensitivity and cooperativity of Ca(2+) activation or qualitative alterations in SPH-induced changes in Ca(2+)-activated contraction. Data suggest that the force loss is mediated by cycling cross-bridges, and might reflect a reduction in force generated by individual cross-bridges.

Topics: Actin Cytoskeleton; Adenosine Triphosphate; Animals; Calcium; Calcium Signaling; Cattle; Dose-Response Relationship, Drug; Hydrogen-Ion Concentration; Muscle Contraction; Muscle Weakness; Myocardium; Myocytes, Cardiac; Myosins; Phalloidine; Sus scrofa

Effects of T8993G mutation in mitochondrial DNA (mtDNA), associated with neurogenical muscle weakness, ataxia and retinitis pigmentosa (NARP), on the cytoskeleton, mitochondrial network and calcium homeostasis in human osteosarcoma cells were investigated. In 98% NARP and rho(0) (lacking mtDNA) cells, the organization of the mitochondrial network and actin cytoskeleton was disturbed. Capacitative calcium entry (CCE) was practically independent of mitochondrial energy status in osteosarcoma cell lines. The significantly slower Ca(2+) influx rates observed in 98% NARP and rho(0), in comparison to parental cells, indicates that proper actin cytoskeletal organization is important for CCE in these cells.

Topics: Actins; Ataxia; Benzimidazoles; Calcium; Carbocyanines; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cell Line, Tumor; Cytoskeleton; DNA, Mitochondrial; Fluorescent Dyes; Fura-2; Humans; Image Processing, Computer-Assisted; Immunohistochemistry; Ionophores; Membrane Potentials; Microscopy, Fluorescence; Mitochondrial Myopathies; Muscle Weakness; Mutation; Osteosarcoma; Phalloidine; Retinitis Pigmentosa; Rhodamines; Thapsigargin