The origin of the anticholinesterase-induced repetitive activity of the phrenic nerve-diaphragm preparation of the rat in vitro

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Abstract
1 Action potentials have been recorded in contracting muscle cells of the phrenic nerve-diaphragm preparation from rats. After the organophosphorous anticholinesterase, ecothiopate, some cells fired repetitive action potentials. In 0.1 mm [Mg2+]o the repetitive activity was generated presynaptically or postsynaptically, and in 1 mm [Mg2+]o, probably only postsynaptically. 2 The repetitive action potentials in muscle were generated ectopically about 0.2 mm away from the usual site. 3 In mm [Mg2+]o, spontaneous action potentials in muscle were generated presynaptically. These were often followed by repetitive action potentials generated either presynaptically or postsynaptically. 4 The initiation of centripetal action potentials in the phrenic nerve was coincident with the repetitive firing in the muscle. 5 The results are discussed in relation to the manner of generation of repetitive activity in nerve and muscle after anticholinesterases.