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 mutant strains of Paramecium Were studied. From measurements of survival and cell motility under the continuous application of light in the presence of MB, the mutant strains remained alive for about three times longer than the wild-type strain. Although the resting potential of the mutant cells was similar to that of wild-type cells, the continuous photodynamic action shifted the membrane potentials of the mutant and wild-type cells to a depolarized level and a hyperpolarized level, respectively, from that before light application. Under voltage clamping, the mutant cells reduced not only the outward current elicited by the photodynamic action but also the outward tail current elicited by the preceding pulse of hyperpolarization. We conclude that the mutant strain is defective in the activation of Ca(2+)-dependent K+ channels. This defect might cause a reduction in the Ca2+ influx because of the suppression of the membrane hyperpolarization, which results in the elongation of survival time under the photodynamic action.
Saitow
F
F
Department of Biophysical Engineering, Osaka University, Japan.
Nakaoka
Y
Y
D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000528:radiation effects; D007473:Ion Channels / Q000187:drug effects*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008027:Light; D008564:Membrane Potentials / Q000528:radiation effects; D008751:Methylene Blue / Q000494:pharmacology*; D010247:Paramecium / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D018462:Photobiology; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects; D024681:Potassium Channels, Calcium-Activated
D007473:Ion Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D017319:Photosensitizing Agents; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011188:Potassium; D008751:Methylene Blue