Dye absorption changes in single muscle fibers: an application of an automatic balancing circuit.

It is very difficult to record small potential changes in the presence of a large background voltage that drifts. This is particularly true in recording optical changes during excitation of nerve and muscle because the optical changes are usually very small compared with the background. We describe a convenient circuit, which is useful under these circumstances. This circuit automatically balances the background drift. Using this circuit we recorded light absorption changes during excitation of single muscle fibers stained with a fluorescence dye merocyanine 540. The optical change consists of three components. The first component presumably reflects the action potential of the surface membrane and the T-system. The second and the third components are perhaps the movement artifacts from latency relaxation followed by contraction.