INTRODUCTION AND OBJECTIVES: Botulinum neurotoxin-A (BoNT/A) is one of novel therapeutic agents for urinary dysfunction including OAB. The inhibitory mechanism of BoNT/A in the bladder is considered mainly as that it cleaves synaptosome-associated protein of 25,000 daltons (SNAP-25), resulting in failure of acetylcholine exocytosis from efferent nerve terminals. On the other hand, we reported that BoNT/A had inhibitory effects on muscle contraction and L-type voltage-gated Ca channel (VGCC) activity in detrusor smooth muscle (AUA 2009). In this study, we further investigated the effects of BoNT/A on T-type VGCC in rat detrusor smooth muscle. METHODS: Bladder smooth muscle strips were obtained from female rats. Single myocytes were obtained by enzymatic digestion, and VGCC was investigated using barium as a charge carrier in whole-cell patch-clamp methods. We administrated BoNT/A light chain (BoNT/A-LC) or a peptide that designed as C-terminus 9 amino-acids of SNAP-25 (SNAP-25C) directory into the cytosol through a patch pipette. RESULTS: In control condition with normal pipette solution, T-type inward currents were evoked by depolarization to 40 mV from the holding potential of 90 mV, and the currents were not inhibited by nifedipine 5 M, a L-type VGCC blocker but abolished by NiCl2 500 M. We monitored the time course of peak amplitude of T-type inward currents. After 16 min intracellular perfusion of control pipette solution, the peak amplitude of T-type current did not change (relative value to control, 1.1 0.12, n 6). However, after 16 min perfusion of BoNT/ A-LC 100 nM, the peak amplitude of T-type current was significantly increased (relative value to control, 1.6 0.082, n 6). Similar result was demonstrated by intracellular perfusion of SNAP-25C 1 M (relative value to control, 1.4 0.16, n 6). Time to peak of T-type current was prolonged after intracellular perfusion of BoNT/A-LC or SNAP25C. In the analysis of steady-state inactivation of T-type VGCC in the presence of nifedipine 5 M, the Vh value in BoNT/A-LC 100 nM or SNAP-25C 1 M intracellular administrated group was significantly deeper than that in control group ( 52 2.5 mV (n 6) in control group, 62 0.66 mV (n 6) in BoNT/A-LC group and 66 3.6 mV (n 5) in SNAP-25C 1 M group). CONCLUSIONS: These results suggest that BoNT/A changes the ion channel kinetics of T-type VGCC in detrusor smooth muscle, and this effect seems to be mediated by cleaved SNAP-25 Cterminus. The negative shift of Vh values of T-type VGCC after BoNT/A treatment might contribute to a BoNT/A-induced reduction in detrusor muscle contractility in OAB patients.