兼受快肌和慢肌神经支配的大鼠慢肌或快肌纤维的肌-腱接头都没有乙酰胆碱敏感性

在大鼠慢肌比目鱼肌(SOL)肌纤维的肌-腱接头(MTJ)上有较高的乙酰胆碱(ACh)敏感牲,而快肌伸趾长肌(EDL)的 MTJ却没有。SOL 肌纤维受 EDL神经交叉支配后,其 MTJ的 ACh敏感性消失,此点 Miledi等已有报道。本文首先验证了与此相对称的结果,即EDL 肌纤维受 SOL神经交叉支配后,其 MTJ获得与正常 SOL肌纤维 MTJ相似的 ACh敏感性,从而进一步肯定了MTJ 的ACh 敏感性的出现是由特殊神经支配决定的。本文的主要结果是:兼受 SOL神经和 EDL神经支配的EDL和SOL的纤维,其MTJ都没有AGh 敏感性。这一结果的兴趣,不但在于它显示当两种神经支配同时存在时,快肌神经的影响压倒慢肌神经,而且还在于此结果与以往用其他指标进行的双神经支配肌纤维实验的结果形成鲜明的对照:用 M-ATPase 组织化学染色和Z带宽度等变化为指标,在双神经支配肌纤维中,慢肌神经的影响总压倒快肌神经。我们也观察了长期电刺激对MTJ ACh敏感性的影响。SOL经“慢”型刺激2—3周后,其 MTJ的 ACh敏感性虽有降低,但不及“快”型刺激显著。综合各种有关的观察,本文对双神经支配肌纤维的 MTJ没有 ACh敏感性这一主要结果的解释进行了讨论。

THERE IS NO ACETYLCHOLINE SENSITIVITY AT THE MYOTENDINOUS JUNCTION OF FAST-OR SLOW-MUSCLE FIBRES WITH COMBINED FAST-AND SLOW-MUSCLE NERVE SUPPLIES IN RATS

At the myotendinous junction (MTJ) the slow-twitch muscle soleus (SOL)of the rat has considerable acetylcholine (ACh) sensitivity, whereas the fast-twitchmuscle extensor digitorum longus (EDL) has practically none. Miledi et al.showed that in SOL cross-innervated by EDL nerve, MTJ ACh sentitivity is lost.In the present work, it was observed that ACh sensitivity, comparable to that foundat normal SOL MTJs can be made to appear at MTJs of EDL when cross-innervatedby SOL nerve. Therefore, it is further confirmed that the emergence of MTJACh sensitibity is determined by special innervation. Our main result is thatMTJ ACh sensitivity can not be found on either EDL or SOL fibres if they receiveinnervation from both SOL nerve and EDL nerve, an observation showing evidentlythe dominance of the fast-muscle nerve over the slow-muscle nerve in determiningMTJ ACh activity when both nerves coexist. This is also in striking contrast withthe previous observation that the influence from slow-muscle nerve always dominatesthat of fast-muscle nerve if M-ATPase histochemical staining and ultrastructuralfeatures like Z-band width of doubly innervated fibres are used as criteria. Wealso observed the effect of long-term electrical stimulation on MTJ ACh sensitivity.Although 'slow' pattern stimulation for 2 or 3 weeks is shown to depress ACh sen-sitivity at SOL MTJs, it is less effective than 'fast' pattern stimulationt. Theexplanation for the absence of MTJ ACh sensitivity on doubly innervated fibresare discussed in light of these results.