Cytoplasmic Ca2+ oscillations evoked by acetylcholine or intracellular infusion of inositol trisphosphate or Ca2+ can be inhibited by internal Ca2+.

In single internally perfused mouse pancreatic acinar cells, changes in the free intracellular Ca2+ concentration ([Ca2+]i) were monitored by measuring the Ca2(+)-dependent transmembrane Cl- current under voltage-clamp conditions. Cytoplasmic Ca2+ oscillations were induced by external acetylcholine (ACh) application, internal infusion of inositol (1,4,5) trisphosphate or its non-metabolizable analogue inositol trisphosphorothioate or by intracellular Ca2+ infusion. Such [Ca2+]i oscillations could be rapidly inhibited by external application of the Ca2+ ionophore ionomycin (10-100 nM). Cytoplasmic Ca2+ oscillations could also be evoked by external caffeine (1 mM) application when the internal perfusion solution did not contain any Ca2+ chelator. In such cases intracellular Ca2+ infusion transiently abolished the [Ca2+]i oscillations. We conclude that although Ca2(+)-induced Ca2+ release is the cause of the ACh-evoked [Ca2+]i oscillations, there is also a negative feed-back since Ca2+ can inhibit Ca2+ release initiated by Ca2+.