THE PHOTODYNAMIC-ACTION OF METHYLENE-BLUE ON THE ION CHANNELS OF PARAMECIUM CAUSES CELL-DAMAGE

The photodynamic effects of methylene blue (MB) on wild-type and mutan t strains of Paramecium Were studied. From measurements of survival an d cell motility under the continuous application of light in the prese nce of MB, the mutant strains remained alive for about three times lon ger than the wild-type strain. Although the resting potential of the m utant cells was similar to that of wild-type cells, the continuous pho todynamic action shifted the membrane potentials of the mutant and wil d-type cells to a depolarized level and a hyperpolarized level, respec tively, from that before light application, Under voltage clamping, th e mutant cells reduced not only the outward current elicited by the ph otodynamic action but also the outward tail current elicited by the pr eceding pulse of hyperpolarization. We conclude that the mutant strain is defective in the activation of Ca2+-dependent K+ channels. This de fect might cause a reduction in the Ca2+ influx because of the suppres sion of the membrane hyperpolarization, which results in the elongatio n of survival time under the photodynamic action.