PERCHLORATE DIFFERENTIALLY POTENTIATES EXCITATION-CONTRACTION COUPLING OF DIAPHRAGM MUSCLE FROM MDX AND CONTROL MICE

The effects of perchlorate (6-40 mM) on contractile properties and dep olarization-contraction coupling of diaphragm have been tested in musc le fibre bundles from 8 to 12-week-old mdx and control mice. Twitch co ntractile properties were affected by perchlorate to a similar extent in mdx and control muscles. in the absence of perchlorate, voltage-dep endent parameters of both activation and inactivation were similar in mdx and control muscles. In both mdx and control muscles, perchlorate induced a shift of activation and inactivation curves toward more nega tive potentials. However, mdx diaphragm fibres were less sensitive to perchlorate in the low range of concentrations (6-12 mM). These result s are unlikely to be due to a possible effect of the lack of dystrophi n on the excitation-contraction coupling voltage sensor or ryanodine r eceptor. However. necrosis and regeneration occur in mdx mouse diaphra gm and it is postulated that the presence of a high proportion of not fully mature fibres could contribute to the reduced sensitivity of mdx diaphragm fibres to perchlorate.