Effect of purified Clostridium difficile toxins on intestinal smooth muscle. II. Toxin B.

In the companion paper [Am. J. Physiol. 256 (Gastrointest. Liver Physiol. 19): G759-G766, 1989] we showed that highly purified Clostridium difficile toxin A had a profound effect on intestinal smooth muscle after in vivo but not in vitro exposure. In this study we assessed the effects of in vivo and in vitro exposure to C. difficile toxin B on simultaneous measurements of intracellular membrane potential and contractility in rabbit ileal smooth muscle. Direct exposure of ileal smooth muscle to toxin B (0.1-60 micrograms/ml) in vitro caused membrane depolarization and inhibition of action potential frequency, amplitude, and peak voltage, but no effect on slow wave frequency or amplitude was seen. Toxin exposure also resulted in inhibition of the amplitude of carbachol-induced contractions, with phasic contractions being significantly more sensitive to the effect of toxin B than tonic contractions over the complete dose range. The electromechanical effects of toxin B were not affected by prior administration of tetrodotoxin, atropine, hexamethonium, or phentolamine. In contrast, toxin B administered in vivo into an isolated ileal loop had no effect on spontaneous electromechanical properties of excised smooth muscle strips. Our results indicate that direct exposure in vitro of ileal smooth muscle to C. difficile toxin B causes membrane depolarization in association with inhibition of electromechanical activity. This effect, in combination with the indirect effects of toxin A, may contribute to altered intestinal motility during diarrhea caused by C. difficile.