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Block of light responses of salamander rods by pertussis toxin and reversal by nicotinamide
Author(s) -
Falk G.,
Shiells R.A.
Publication year - 1988
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(88)80812-3
Subject(s) - visual phototransduction , pertussis toxin , adp ribosylation , toxin , biophysics , nicotinamide , phospholipase c , chemistry , microbiology and biotechnology , biochemistry , biology , pharmacology , retinal , g protein , enzyme , nad+ kinase , receptor
Transducin is the substrate for a pertussis toxin‐catalyzed ADP‐ribosylation in isolated retinal rod disk membranes [(1984) J. Biol. Chem. 259, 23–26]. The effects of the toxin on the light responses of intact dark‐adapted rods were studied. Applied close to a rod outer segment in a retinal slice, pertussis toxin depolarized the rod by a few millivolts and produced a long‐lasting depression of light responses, effects which depended on penetration of toxin into rods. Nicotinamide, an inhibitor of ADP‐ribosylation, not only blocked the action of the toxin, but also reversed the effects once established. The action of nicotinamide itself on rods indicates the presence of endogenous ADP‐ribosyltransferases which may constitute a control system modulating phototransduction. Inhibition of phospholipase C by neomycin had only transient effects indicating that the cGMP, rather than a phosphoinositide, pathway is primary in vertebrate phototransduction. Rapid reversal of pertussis toxin action suggests possible clinical applications of nicotinamide or congeners to the treatment of disease caused by ADP‐ribosylating bacterial toxins.