Photodynamic alteration of Eosin Y-sensitized lobster giant axons was compared under conditions of calcium-rich and calcium-free media, to see whether the conflicting reported descriptions of the photodynamic effect can be resolved in terms of variations in calcium content of the bathing medium. Both a voltage clamp analysis (sucrose gap technique) and a microelectrode analysis (nonclamped axons) were used. In calcium-free media the characteristic photodynamic alterations of sodium channels (reduction in maximum conductance; increase in time to peak current) occurred at 40% slower rates than in calcium-rich media, while the characteristic decrease in potassium current was unaffected by the calcium content. Photodynamic alteration depolarized nonvoltage clamped axons in both media, and there was an initial rapid depolarization phase in calcium-free media. All of these changes in both media were irreversible. In calcium-free media photodynamic alteration usually induced repetitive firing. The firing showed apparent reversibility, since it stopped after a period of time and could usually be reinitiated upon further illumination. It is proposed that decalcification does not alter the basic nature of the photodynamic effect, but complicates the axon response by its own independent effects.
ASJC Scopus subject areas
- Cell Biology