Electrophysiological study of the action of neurotensin on the smooth muscle of the guinea-pig taenia coli.

The effects of neurotensin on the membrane potential and conductance, and on the tension of the guinea-pig taenia coli were investigated using the sucrose gap method. In preparations spontaneously active at 37 degrees C, neurotensin (0.5--10 nM) increased the frequency of spikes and induced a smooth muscle membrane depolarization which led to a block of spike discharges. These electrical events were accompanied by phasic and tonic contractions of the smooth muscle. At 20 degrees C the guinea-pig taenia coli exhibited little or no spontaneous activity. Neurotensin (50 nM) rapidly depolarized the smooth muscle membrane and increased its conductance. Concentration--response curves of neurotensin-induced depolarization and contraction gave an EC50 of 1.7 nM and 4.5 nM respectively, with a maximally effective concentration of peptide around 50 nM for both effects. Studies in modified or substituted salt solutions indicated that the neurotensin-induced increase in smooth muscle membrane conductance was primarily due to an increase in Na+ and Ca2+ conductances.