THE EFFECT OF CÆSIUM IONS ON NEUROMUSCULAR TRANSMISSION IN THE FROG

¹ Department of Pharmacology, University of Edinburgh Medical School, Edinburgh, Scotland

The effect of Cs⁺ on neuromuscutlar transmission in the frog has been investigated. In both K⁺-containing and K⁺-free solutions, the presence of Cs⁺ allowed a gradual increase in the amplitude of the evoked end-plate potential (e.p.p.) which was due to an increase in the output of transmitter. However, after prolonged exposure to Cs⁺ in K⁺-free solutions, the duration of the e.p.p. was increased and its amplitude progressively reduced, eventually to zero. The effects of Cs⁺ were reversible. The results are consistent with the idea that exposure to Cs⁺ ions allows their entry into nerve terminals in exchange for K⁺ ions, thereby resulting in an increased duration of the projunctional action potential.