Facilitation of frog neuromuscular transmission by sodium fluoride.

1. The effects of sodium fluoride (NaF, 5 mM) alone or in combination with theophylline (1.5 mM) or imidazole (1.5 mM) on the amplitude of the endplate potential (e.p.p.), frequency of the miniature endplate potential (m.e.p.p.), and the quantal content of the e.p.p. of bullfrog muscle were investigated. The effects of forskolin (1 microM) and papaverine (1 microM) on the m.e.p.p. frequency were also studied. 2. NaF caused an increase of 22% in the amplitude of the e.p.p. This NaF-induced increase was enhanced by theophylline (to 51%) and reduced by imidazole (to 10%). 3. Papaverine (0.1-3 microM) increased the frequency of m.e.p.ps. Forskolin at 1 microM raised the m.e.p.p. frequency by 13%. The effect was increased to 31% by 1 microM papaverine. NaF also raised the m.e.p.p. frequency by 90%. This action too was increased by theophylline (2.6 fold) and by papaverine (2.1 fold); however, it was reduced by imidazole (1.3 fold). 4. NaF increased the quantal content of the e.p.p. by 28%. This effect was enhanced by theophylline to 44%, while it was diminished by imidazole. 5. These results suggest that an increase in the transmitter release via an elevation of cyclic AMP may be involved in the facilitation of neuromuscular transmission by NaF.