Rat duodenal smooth muscle contractile responses to angiotensin II are dependent on calmodulin.

1. Isolated duodenal segments were pretreated with either of the calmodulin inhibitors proadifen or trifluoroperazine and the subsequent contractile force and frequency response to angiotensin II monitored. 2. Both proadifen and trifluoroperazine decreased the spontaneous contractile force and frequency in isolated perfused duodenal segments and attenuated the force generation following exposure to angiotensin II. Proadifen and trifluoroperazine also altered the qualitative behaviour of duodenal segments. 3. These results suggest that the action of angiotensin II on duodenal smooth muscle motility is dependent on calmodulin. Furthermore, the change in qualitative behaviour of duodenal segments following treatment with calmodulin inhibitors suggest that the function of intrinsic intestinal neurons is also altered.