Different effects of toosendanin on perineurially recorded Ca2+ currents in mouse and frog motor nerve terminals

By perineurial recording, the effects of toosendanin (TSN), a presynaptic b locker, on nerve terminal calcium currents (I-Ca) were observed in innervat ed triangularis sterni of the mouse and cutaneous pectoris of the frog. It was found that TSN blocked the slow component of I-Ca insensitive to nifedi pine and omega -conotoxin-GVIA, and increasing the extracellular Ca2+ conce ntration partially antagonized the inhibitory effect in mouse motor nerve t erminals. However, in the frog, TSN increased the slow component of I-Ca an d this effect disappeared in the presence of nifedipine in perfusion soluti on. Based on previous data showing that the slow component of I-Ca. were me diated by different subtypes of calcium channels in mouse and frog motor ne rve terminals, we presume that TSN could exercise different effects on vari ous subtypes of calcium channels. (C) 2001 Elsevier Science Ireland Ltd. an d the Japan Neuroscience Society. All rights reserved.