[The postsynaptic effects of substance P in the frog neuromuscular synapse]

The effect of substance P on the end-plate currents (EPC) and miniature EPC (MEPC) was studied in the "cut" sartorius muscle of the frog using voltage-clamp technique after acetylcholinesterase inhibition. Substance P in the concentration 5.10(-7)-1.10(-6) mol/l had no effect on the amplitude and time course of the single EPC and MEPC, but promoted significant prolongation of EPC decay during repetitive nerve stimulation (10/s), which indicated development of postsynaptic potentiation. Elevation of the substance P concentration to 5.10(-6) mol/l has led to the shortening of single EPS decay and more significant depression of the EPC amplitude in trains. This effect was connected with a decrease of the postsynaptic membrane sensitivity to acetylcholine, i. e. development of desensitization.