Fig. 2. Measurement of Ca²⁺ release and Ca²⁺ influx in cells from wild-type and SERCA2^+/– mice. In (A–C), cells from wild-type (solid lines) or SERCA2^+/– mice (dashed lines) were incubated in Ca²⁺-free medium prior to stimulation with 1 mM carbachol. After reduction of [Ca²⁺]_i to a stable level, the cells were incubated with a solution containing 2 mM CaCl₂ to estimate the rate of Ca²⁺ influx. In (B) and (C), the cells were treated with 5 µM thapsigargin to inhibit any remaining SERCA pump activity prior to initiation of Ca²⁺ influx. To measure directly Ca²⁺ uptake and release from internal stores, pancreatic acini from wild-type (D and F) or SERCA2^+/– mice (E and F) were permeabilized by addition of cells to an SLO-containing medium. When medium Ca²⁺ was reduced to a stable level, incremental concentrations of IP₃ were added to estimate the extent and potency of IP₃-mediated Ca²⁺ release.