| Abstract: | 運動神經元的神經軸所傳遞的神經脈衝傳至神經肌肉接合處 (NMJ) 轉換成化學訊號，並將此訊號通過神經肌肉間隙到達突觸後肌肉膜上之nAChR (Nicotinic acetylcholine receptor)，最終引發骨骼肌的收縮。已知右旋筒箭毒 (d-tubocurarne, d-TC) 是nAChR的阻斷劑，能夠有效的抑制神經引發的骨骼肌收縮、終板電位 (End-plate potentials, Epps) 與微小終板電位 (Miniature-end-plate potentials, Mepps) 之振幅。Suramin為抗錐型蟲的藥物，並且為P2嘌呤受體 (P2-purinoceptor) 的拮抗劑，而suramin與d-TC有相類似的結構。前處理suramin (100 µM) 與suramin的衍生物NF449 (100 µM) 對於d-TC (5 µM) 造成的神經引發骨骼肌收縮、Epps或是Mepps的阻斷，都有顯著的拮抗作用；而與suramin另一個衍生物NF007 (100 µM) 相較之下，沒有有效的影響d-TC造成神經肌肉之阻斷。因此，前處理suramin與NF449不僅能夠拮抗d-TC阻斷神經肌肉傳訊，並且後處理也能扭轉d-TC的阻斷，但是對於突觸後雨傘節神經蛇毒 (α-BTX) 並沒有影響。由於在小雞二頸肌實驗中，suramin和NF449能有效的拮抗d-TC抑制ACh作用於nAChR (d-TC單獨為49.8 ± 3.3 ％ ；前處理suramin則d-TC抑制ACh作用為 67.8 ± 3.4 ％, P = 0.0001；前處理NF449則d-TC抑制ACh作用為 93.2 ± 7.5 ％, P < 0.0001)，結果顯示suramin與NF449能和d-TC在nAChR上競爭。除此之外，藉由肋神經-胸三角肌神經末梢電流之測定，排除了suramin與NF449對於突觸前神經軸鈉和鉀離子流的影響。這些發現顯示suramin與NF449在nAChR上，能有效的對於d-TC造成神經肌肉阻斷產生拮抗作用。我們推測此拮抗作用可能是去干擾或阻礙d-TC作用於nAChR上結合位。
Moter neurons conduct nerve impulses down an axon to the synaptic terminal to induce neurotransmitter release at the axon terminal. The neurotransmitter binds to nicotinic ACh receptor (nAChR) and eventually produce the muscle contraction. As we known a nAChR antagonist, d-tubocurarine (d-TC), can inhibit the amplitudes of nerve-evoke muscle tension, end-plate potential (epp) and miniature end-plate potential (mepp). Suramin is known as an anti-trypanosomal drug and an antagonist of P2-purinoceptor, and it’s chemical structure resembles d-TC. The pretreatment with either suramin (100 µM) or suramin analogue NF449 (100 µM) significantly antagonizes the effects of d-TC (5 µM) on the nerve-evoke muscle tension, epps and mepps. Another suramin analogues, NF007 didn’t have significant effects on neuromuscular transmission blockade induced by d-TC. However, pretreatment with suramin or NF449 does not antagonize the effects of α-bungarotoxin, can irreversible nAChR blocker. Since either suramin or NF449 is able to antagonize the inhibition on nAChR produced by d-TC in the chick biventer-cervicis muscle (d-TC alone, 49.8 ± 3.3 ％ of control；pretreatment with suramin and post-treatment with d-TC, 67.8 ± 3.4 ％ of control, P = 0.0001；pretreatment with NF449 and post-treatment with d-TC, 93.2 ± 7.5 ％ of control, P < 0.0001), it is suggested that the effects of suramin and NF449 are to compete the d-TC binding site on the nAChR. Furthemore, we ruled out the possibility of presynaptic mechanism due to the nerve terminal waveform of triangularis sterni are not affected by suramin and NF449. Our experiments demonstrated that suramin and NF449 but not NF007 can antagonize the inhibition of neuromuscular transmission induced by d-TC. We speculated that the antagonistic effect of suramin and suramin analogues, may be to compete the d-TC binding site of nAChR. |
