The wavelength dependence of optically recorded action potentials in the atrial muscles of the bullfrog (Rana catesbeiana).

The action potentials from frog atrial muscles that had been stained with either merocyanine rhodanine or merocyanine oxazolone dyes were recorded optically. Then the dependence of the maximum rising phase of the optically recorded action potential on the wavelength of the incident beam was analyzed. The atrial muscle stained with two kinds of dyes showed no wavelength dependence in the duration of the rising phase (defined in Fig. 1) in the maximum rising phase of the action potential. These results were consistent with the structure of the membrane system of the frog heart. However, for the atrial muscles stained with merocyanine oxazolone dye, the optical signals recorded at 718 nm of the incident beam showed a second rising phase after the initial rapid rising phase of the optical signal, and this phase was not observed in the optical signals recorded at other wavelengths.