System for automatic activation of skinned muscle fibers

A system is described for automatically changing the solutions surrounding skinned muscle fibers at a controlled temperature. The system consists of a complex muscle chamber and solenoid valve-controlled vacuum-driven syringe pumps. The chamber has a muscle trough, a conduit for circulating coolant, and channels for precooling solutions. After traveling through the cooling channels, the solutions are injected into one end of the muscle trough and removed by suction at the other. The volume of the trough (approximately 40 microliter) is kept as low as possible to minimize the amount of solution required for complete solution exchange (approximately 400 microliter). Solution changes are complete within 400 ms. The timing of the sequence of solution changes is precisely controlled by digital timers that activate the solenoid valves of the pumps. By exposing the fibers briefly to a high concentration of free calcium and then changing to a buffered calcium solution, it is possible to achieve steady tension levels in 1-2 s, even when partially activating the fibers. Such rapid partial activation is possible because the exposure to free calcium can be precisely timed. The timers also allow the solution changes to be synchronized with other perturbations.