Effects of pseudomonas toxin A, diphtheria toxin, and cholera toxin on electrical characteristics of turtle bladder.

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Abstract
Rapidly developing changes in the short-circuiting current (Isc), conductance (G) and potential (PD) of turtle bladders in Na-rich or Na-free media are seen after the mucosal addition, at 10 nM, of each of 3 toxins containing ADP-ribosylation activity: P. aeruginosa toxin A, diphtheria toxin and cholera toxin. Toxin A irreversibily decreased the Isc, PD and G of bladders in Na-rich media and the Isc and PD of bladders in Na-free media. Diphtheria or cholera toxin reversibly increased Isc and PD (not G) but only in Na-free media. Toxin A effects in turtle bladder, like those in other host cell systems, were eliminated by pre-exposure of this toxin to heat, specific antitoxin or dithiothreitol and urea. Because exposure to this last condition increases the ADP-ribosylation activity of toxin A, the proenzyme may be the required transport-inhibiting toxin A form. Effects of all 3 toxins occurred rapidly, possibly before any intracellular ADP-ribosylation reactions are initiated. Whereas a recognition toxin binding to receptors on the apical membrane completely accounts for reversible effects of diphtheria or cholera toxin, this and additional toxin-membrane interactions (e.g., translocation) are needed to account for the irreversible toxin effects.