The Effect of Replacement of Potassium by Cesium Ions on Neuromuscular Blockade of the Rat Phrenic Nerve – Diaphragm Preparation In Vitro

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Abstract
The effect of potassium replacement by cesium in the rat diaphragm preparations has been investigated using conventional intracellular recording techniques; end-plate potentials (EPP's) recorded in modified Krebs' solution with lowered Ca2+ and high Mg2+ were increased until twitching in response to indirect stimulation was restored. This increase in amplitude of the EPP was not acccompanied by any change in the magnitude or frequency of miniature end-plate potentials (MEPP's) suggesting that Cs+ is acting presynaptically to increase evoked release of transmitter. Similar augmentations of EPP's were observed in preparations paralyzed with d-tubocurarine, gallamine, pancuronium, or decamethonium. Parallel studies showed that the mechanical response of the preparations returned towards control values after K+ substitution by Cs+ in diaphragms that were blocked by the above agents but not those blocked by hemicholinium.The results are consistent with the conclusion that the presynaptic action of cesium can overcome directly any effect that the clinically used blocking agents may have on presynaptic sites and that the increased release of transmitter by cesium is sufficient to overcome indirectly the depressant effects of the blocking agents at postsynaptic end-plate receptors.

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