Influence of calcium removal from bath solution on isolated rat duodenum contractions.

In this study whether extracellular Ca++ is essential to produce an increase of tension of isolated rat duodenum by ACh, 5-HT, AVP and KCl-, was examined. KCl- and AVP-evoked contractions were almost totally prevented by Ca++ removal from bath solution. The increase of tension of isolated duodenum caused by ACh or 5-HT was totally prevented after adding nifedipine, a Ca++ channel blocker, into Ca free solution. Our results suggest that ACh or 5-HT utilizes intracellular as well as extracellular sources of Ca++ to produce contraction in rat duodenum, whereas AVP-or KCl evoked contraction was mainly due to influx of Ca from extracellular sources.