Photosensitive signal transduction induces membrane hyperpolarization in Paramecium bursaria.

The protozoan ciliate Paramecium bursaria exhibits membrane hyperpolarization in response to photostimulation, accompanied with an increased swimming speed. The external addition of cyclic nucleotide phosphodiesterase (PDE) inhibitors, either theophylline (1,3-dimethylxanthine) or 3-isobutyl-1-methylxanthin (IBMX), increased in both amplitudes of the membrane hyperpolarization and the increase in swimming speed. Moreover, the addition of membrane permeable cyclic nucleotide analogs, either 8-bromo-adenosine 3',5'-cyclic monophosphate (Br-cAMP) or 8-Br-guanosine 3',5'-cyclic monophosphate (Br-cGMP), increased these amplitudes.