Effects Of Toosendanin On Calcium Channel, Intracellular Free-Ca～(2+) Concentration And Ca～(2+)-sensitivity Of Neurotransmitter Release Machinery

Toosendanin (C30H38O11, FW 574, TSN), a triterpenoid derivative, is an active B B B B B Bingredient extracted from the bark of Melia toosendan Seib et Zucc which is used inChinese traditional medicine as an anthelmintic vermifuge against ascarids. It wasdemonstrated to be a selective presynaptic blocker in neuromuscular junction andcentral synapses. It also had antibotulismic effect and could induce celldifferentiation and apoptosis. In view of the tight relation between TSN actions andCa2+, the effects of TSN on calcium currents in motor nerve terminals, intracellular P Pfree-Ca2+ concentration ([Ca2+]i) and the Ca2+-sensitivity of release machinery were P P P P B B P Pstudied to elucidate the action mechanism of TSN. The main results obtained weredescribed as followed: 1. By use of perineurial recording technique in cutaneous pectoris of frog, weobserved the effects of TSN on calcium currents in motor nerve terminals. The resultshowed that TSN increased slow component of calcium current in frog and thiseffect disappeared in the presence of nifedipine, a specific blocker of L-type calciumchannel. 2. The effects of TSN on regulation of [Ca2+]i in NG108-15 cell were P P B Binvestigated by laser confocal microscopic calcium imaging. TSN induced increasein high K+-evoked Ca2+ transient and in resting [Ca2+]i in differentiated NG108-15 P P P P P P B B 3摘要cells. The effect depended on extracellular free-Ca2+ and could be blocked by P Pnifedipine. 3. TSN obviously inhibited the glutamate (Glu), a principally excitatoryneurotransmitter in central synapses, release evoked by KCl depolarization in aconcentration- and time-dependent manner. The effect mainly resulted from TSN-induced block of the Ca2+-dependent transmitter release. After TSN application the P PGlu release evoked by elevating [Ca2+]i with A23187 also significantly decreased. P P B B Based on the results above, it was proposed that through facilitating the L-typecalcium channels on peripheral and central synapses TSN cause increase in [Ca2+]i P P B Band result in intracellular Ca2+ overload, which might be responsible for the TSN- P Pinduced loss of the release machinery sensitivity to Ca2+ and the final inhibition of P Pneurotransmitter release. The increase in [Ca2+]i may also be involved in the P P B Bantibotulismic effect of TSN and the TSN-induced cell differentiation and apoptosis.