Requirement of intestinal Ca²⁺ oscillations on extracellular Ca²⁺. Representative experiment showing the effect of extracellular Ca²⁺ removal on Ca²⁺ oscillations. Calcium-free extracellular solution was buffered with 1 mM EGTA. Removal of bath Ca²⁺ causes rapid inhibition of Ca²⁺ oscillations and drop in total fluo-4 fluorescence (similar results were observed in five out five intestines). Addition of Ca²⁺ back to the bath causes a rapid increase in fluo-4 fluorescence and recovery of Ca²⁺ oscillations (similar results were observed in four out of four intestines).