Action of decamethonium iodide (C 10) on the demarcation potential of cat's muscle / B. Delisle Burns, W.-D.-M. Paton and M. Vianna Dias.

  • Burns, B. Delisle (Benedict Delisle)
Date:
[1949?]
Catalogue details

Licence: In copyright

Credit: Action of decamethonium iodide (C 10) on the demarcation potential of cat's muscle / B. Delisle Burns, W.-D.-M. Paton and M. Vianna Dias. Source: Wellcome Collection.

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    Because Cio has a distinct anticholinesterase action, we have tested t effect of eserine and prostigmine on the DP. These two substances, in dos producing a large increase of the twitch tension and causing strong fascic lations, did not depress the demarcation potential significantly. We have also compared the action of potassium chloride by this techniq; with that of C10. At least 1 to 2 mg. KC1 intraarterially were necessary produce a decrease of DP comparable to that caused by 2 /xg. Ci0. Pentamethonium iodide (C5) by itself did not alter the DP, even in lai doses. It had, however, a weak antagonistic effect on the action of Cio; given first it will diminish (but not prevent) the fall of DP caused by 0 and if given during such a fall, it moderated it slightly. But these effe require big doses, and are small in magnitude compared with the effect i such doses on the neuromuscular block due to Cio. Z)-tubocurarine chloride, in paralysing doses, induced occasionally a sn increase (not more than 5 p. 100) in the DP, but often did not affect} and never reduced it. On the other hand, in doses of 20-200 /xg. ini arterially, it prevented the depolarizing action of Cio; and, if injected dur a fall of DP due to Cio, could reverse this fall and accelerate recove Its actions therefore resemble those of C5, but it is considerably more ef tive. The localization of the depolarization which we have observed in tibi was studied on the cat’s gracilis, which offers a simple muscle preparat with localized end-plate regions and a nerve-free distal extremity [Brc:<! and Burns, 1949]. We observed that, in the uninjured muscle, afters injection of Cio a potential difference appeared between the end-plate re§ and the neighbouring parts of the muscle, the end-plates becoming relati negative. We have found, further, that in the presence of this depolariza of the end-plate region, the muscle fibre stimulated directly gave rise tc action potential propagated as far as the end-plate region, but that the ac potential did not pass this point. After a dose of d-tubocurarine chlo producing an equally profound neuromuscular block, conduction along ; muscle fibre was unaltered. These experiments will be published in full elsewehre. CONCLUSIONS. ti Cio presents a definite and typical depolarizing action on skeletal mt which is localized to the end-plate regions. The fact that this depolarize prevents propagation of the action potential along the muscle fibre sug; £s that it is also responsible for the neuromuscular block caused by Cio. u the other hand, the lack of parallelism between the antagonisms of C5 tc jj^ on neuromuscular block and on demarcation potential indicates thal relation between the block and the depolarization is not a simple one.