Abstract
Skinned muscle fibers provide a powerful means to assess the functional effects of compounds that modulate the sarcomere. The main drawback of this preparation as an assay system is its low-throughput nature. As part of an effort to optimize small molecule activators of the skeletal sarcomere for therapeutic applications in conditions where muscle weakness is a feature, an automated system was designed that can simultaneously run multiple types of isometric force assays. Six identical units, controlled through a single software interface, run a variety of assay protocols. Each unit independently measures the force of a single suspended fiber as it is submerged into various solutions in a temperature controlled block. Assay protocols are unique for each tissue type and desired measurement. Fiber quality is automatically assessed by switching between fully contracting and fully relaxing pCa solutions. If sufficiently robust, fibers are tested by indexing between solutions of varying pCa or compound concentration. In each new solution, the software monitors the rate of force generation and when the fiber has reached a force plateau, automatically moves to the next solution. Control pCa profiles of rabbit psoas fibers measured over a year and a half period show typical variation of < 0.1 pCa unit from historic values. This capability has allowed characterization of several hundred compounds aiding with the selection of a troponin activator as a development candidate for diseases characterized by muscle weakness.
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