The actions of substance P and serotonin on myenteric neurons in tissue culture

Abstract

Intracellular recordings were made from guinea-pig myenteric neurons in tissue culture. The responses to substance P (SP) and serotonin were compared. Putative transmitters were ejected by pressure from micropipettes. The response to SP was, in the majority of cases, a prolonged depolarization, with a latency of 1-5 s and a duration of 1-2 min. During the depolarization there was an increase in the input resistance of the cells, and the excitability was augmented. In two neurons the response to SP was hyperpolarization followed by depolarization. In about 30% of the cells the response to SP was relatively fast, with a duration of less than 10 s and a latency of less than 100 ms. These responses did not show desensitization. Serotonin induced relatively fast responses only, with durations of 0.3-3 s and latencies of 20-50 ms. These responses were usually depolarizing, but in 3 cells were hyperpolarizing. Two types of behaviour were observed during repetitive ejection of serotonin. Some cells showed strong desensitization while in others there was no desensitization and there was even summation. The actions of SP and serotonin were compared by their ejection in the same experiments. The same general properties described above were observed. It is concluded that the two putative transmitters act via distinct response mechanisms. The SP-induced depolarizations in tissue culture resemble in several respects the slow synaptic potentials recorded previously in myenteric neurons in freshly isolated preparations.