Glycolytic type I white muscle fibres lack butyrylcholinesterase activity at acetylcholinergic end plates.

Type I white fibres constitute the pale band of the pigeon serratus metapatagialis (SMP) muscle. The histochemical activity of succinate dehydrogenase (SDH), lactate dehydrogenase (LDH), acetylcholinesterase (AChE) and butyryl cholinesterase (BuChE) was studied in these unique muscle fibres. The muscle fibres possess low SDH but reciprocally high LDH activity. These tonic glycolytic fibres displayed high AChE activity at the myoneural junctions, but the latter lacked BuChE activity. Both AChE and BuChE activities were, however, present at the neuromuscular junctions of the twitch muscle fibres of the SMP muscle. Since BuChE is a precursor in AChE synthesis, the slow-tonic muscle fibres probably depend solely on the AChE transported axonally.