Fig. 1. Estimation of store-operated Mn²⁺ influx in an individual ß-cell. The pancreatic ß-cell was 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 experiment. The medium was then supplemented with 200 µM Mn²⁺ (upper bar) and 30 µM carbachol (Carb; lower bars). The cytoplasmic Mn²⁺ concentration (A) is shown above the calculated Ca²⁺-independent fluorescence of fura-2 compensated for fading and loss of indicator (B); the calculated Ca²⁺-independent fluorescence of fura-2 without such compensation (C) and [Ca²⁺]_i (D), which is not reliable after the introduction of Mn²⁺ (shaded area). The broken lines indicate the rate of change in Mn²⁺ concentration (A) and Ca²⁺-independent fluorescence of fura-2 (B,C) before addition of Mn²⁺ (0), immediately after addition of Mn²⁺ (1) and after subsequent addition of 30 µM carbachol (2).