The inhibitory effect of neurotensin on the motor activity of rabbit ileum: dependence on the ionic environment

The possible ionic mechanisms underlying the inhibitory effect of neurotensin on the spontaneous phasic contractions of the longitudinal muscle of the isolated rabbit ileum were studied by varying the ionic environment. Neurotensin (0.06-60 nM) reduced and abolished the phasic contractions in a concentration-dependent manner. The effect of neurotensin was transient, and the phasic contractions began to recover after 1-3 min although neurotensin was not washed out. The response to neurotensin was very sensitive to alterations in the ionic composition of the bath medium. The changes in the effect of neurotensin brought about by changes in [Na+], [K+], [Ca2+], and [Cl-] suggest that neurotensin hyperpolarizes the smooth muscle. In addition, the effect of combined changes in [Ca2+] and [Cl-] points to a specific role of these ions in the action of neurotensin.