The effects of substance P on neuromuscular transmission in the frog

The effects of substance P (SP) on cholinergic transmission were studied at the neuromuscular junction of frogs by intracellular and voltage-clamp recording methods. Bath application of SP increased the amplitude of end-plate potential (e.p.p.) evoked in either low-Ca2+ -high Mg2+ or curare-containing solution. SP at a concentration of 0.1-1 microM produced a dose-dependent increase in the quantal content of the e.p.p., while having no significant effects on the quantal size. The frequency of m.e.p.p. was increased by SP. SP (1 microM) did not change the sensitivity of nicotinic receptors at the end-plate. These results suggest that SP presynaptically facilitates the neuromuscular transmission, increasing the evoked release of ACh from motor nerve terminals.