Fig. 2. Effect of carbachol concentration on elevation of [Ca²⁺]_i due to store-operated influx of Ca²⁺ in individual ß-cells. Pancreatic ß-cells were loaded with fura-2 in hyperpolarizing medium containing 400 µM diazoxide, 20 mM glucose and 1.28 mM Ca²⁺. The same medium lacking indicator but containing 50 µM methoxyverapamil was present at the beginning of the representative experiment shown in A. The Ca²⁺ concentration was then changed between 1.28 (gray), 0 (white; Ca²⁺-free+2 mM EGTA) and 10 mM (black), as indicated by the upper bars; 0.3-100 µM carbachol was introduced as shown by the lower bars. B shows the dose-response relationship for carbachol-induced elevation of [Ca²⁺]_i in the presence of 10 mM Ca²⁺. A singe observation is shown at 0.3 µM carbachol and means±s.e.m. for six observations at the other concentrations. The solid line shows a fit of the 25 individual data points in the 0.3-30 µM carbachol range to a logistic function (r=0.977; P<0.0001); the broken line shows that the effect decreases at 100 µM carbachol.