High-speed ultrasensitive instrumentation for myofibril mechanics measurements.

A novel instrument for measuring the mechanics of a single myofibril is described. The principle of the transducer operation is to attach a myofibril to a very fine wire suspended in a magnetic field. Feedback circuits pass current through the wire to maintain the length constant when the myofibril contracts. The wire position is measured optoelectronically at a resolution below 1 A. The myofibril measurement system consists of two independent transducers and is capable of resolving tension down to 0.5 ng/square root Hz and controlling the myofibril length with a 10-microseconds rise time. Optical and electronic designs of the system and calibration and adjustment procedures are described. Experimental chamber design, a flow controller, and an environmental noise cancellation scheme are also discussed.