Acetylcholine synthesis at the rat neuromuscular junction.

Acetylcholine (ACh) synthesis in homogenates of rat soleus muscles had two components. One component, specifically inhibited by bromoacetylcholine (BrACh), had a Km for choline of 0.26 mM; the other, resistant to BrACh, had a Km for choline of 45 mM. The component with a low Km was absent from denervated muscle, and was identical in kinetic terms to ACh synthesising activity in homogenates of sciatic nerve. It is therefore considered choline acetyltransferase (ChAT)-specific. The use of BrACh as a specific inhibitor of ChAT activity allowed the calculation of ACh synthesis at individual motor end-plates in the soleus muscle of the rat: 2.1 X 10(-3) nmol h-1. Since the number of muscle fibres and the number of motor units are known for this muscle, ACh synthesis per motor unit could be calculated: 0.15 nmol h-1. It is concluded that BrACh can be used as a specific inhibitor of ChAT activity in homogenates of skeletal muscle and that its use will obviate the necessity of dividing biopsied muscle or small rodent muscles into neural and aneural segments.