Effect of stimulation intensity and botulinum toxin isoform on rat bladder strip contractions

The present experiments compared the inhibitory effects of botulinum toxin A (BoNT-A) and botulinum toxin D (BoNT-D) on neurally evoked contractions of rat bladder strips. We examined the effect of fatigue (trains of 100 shocks at 20 Hz every 20 s for 10 min) followed by non-fatigue stimulation (trains of 100 shocks at 20 Hz every 100 s for 20 min) on the onset of effect and potency of the two toxins. For non-fatigue experiments, strips were untreated (n = 4); or incubated with 1.36 nM BoNT-A (n = 4). During fatigue experiments, strips were untreated (n = 5); or treated with either 1.36 nM BoNT-A (n = 6) or 0.8 nM BoNT-D (n = 6). In non-fatigue experiments, BoNT-A produced significant decreases in contractile area after 1 h of stimulation compared to untreated strips (P < 0.05). After three series of fatigue stimulation, differences in recovery amplitude and area between untreated versus BoNT-A, and untreated versus BoNT-D bladder strips, were statistically significant (P < 0.05). The onset of inhibitory effect was quicker in BoNT-D-treated strips, as a significant reduction (P < 0.05) in recovery of contractile area was observed after 1 h of stimulation compared to both untreated and BoNT-A-treated preparations. In addition, treated (BoNT-A and BoNT-D) and untreated bladder strips responded similarly to atropine, suggesting that the effects of BoNT result from inhibition of both acetylcholine and ATP release. Our results demonstrate that BoNT-D may be a more effective agent to inhibit transmitter release from autonomic nerves of the rat lower urinary tract. Moreover, in our hands, non-fatigue stimulation is as effective as fatigue stimulation in inhibiting bladder strip contractions.