title: Fast and slow inactivation of sodium channels: effects of photodynamic modification by methylene blue.
abstract: Illumination of crayfish giant axons, during internal perfusion with 0.5 mM methylene blue (MB), produces photodynamic effects that include (i) reduction in total sodium conductance, (ii) shifting of the steady-state inactivation curve to the right along the voltage axis, (iii) reduction in the effective valence of steady-state inactivation and, (iv) potentially complete removal of fast inactivation. Additionally, the two kinetic components of fast inactivation in crayfish axons are differentially affected by MB+light. The intercept of the faster component (tau h1) is selectively reduced at shorter MB+light exposure times. Neither tau h1 nor the slower (tau h2) process was protected from MB+light by prior steady-state inactivation of sodium channels. However, carotenoids provide differing degrees of protection against each of the photodynamic actions listed above, suggesting that the four major effects of MB+light are mediated by changes occurring within different regions of the sodium channel molecule.
authors.affiliation: Bekesy Laboratory of Neurobiology, John A. Burns School of Medicine, University of Hawaii, Honolulu 96822.
authors.forename: J G
authors.initials: JG
authors.lastname: Starkus
authors.forename: M D
authors.initials: MD
authors.lastname: Rayner
authors.forename: A
authors.initials: A
authors.lastname: Fleig
authors.forename: P C
authors.initials: PC
authors.lastname: Ruben
mesh_terms: D000818:Animals; D003400:Astacoidea; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D002338:Carotenoids / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008027:Light; D008433:Mathematics; D008751:Methylene Blue / Q000494:pharmacology*; D008954:Models, Biological; D017319:Photosensitizing Agents / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D013997:Time Factors
chemical_list: D017319:Photosensitizing Agents; D015222:Sodium Channels; D002338:Carotenoids; D008751:Methylene Blue