Fig. 4. Effect of CPA 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) and 0 (white; Ca2+-free+2 mM EGTA), as indicated by the upper bars, and 0.3-30 µM CPA was introduced as shown by the lower bars. B shows the dose-response relationship for CPA-induced elevation of [Ca2+]i in the presence of 1.28 mM Ca2+. Means±s.e.m. for 4-5 observations are shown. The solid line shows a fit of the 19 individual data points in the 0.3-10 µM CPA range to a logistic function (r=0.984; P<0.0001) and the broken line that the effect decreases at 30 µM CPA.
