Fig. 2. Influence of presenilin-1 on plasma membrane Ca²⁺ uptake via L-type Ca²⁺ channels. Representative curves (left panels) and respective statistics (right panels) of cytosolic Ca²⁺ measurements in INS-1 cells transfected with either control siRNA or siRNA against presenilin-1. Cells were loaded with the cytosolic Ca²⁺ indicator Fura-2/AM and perfused and imaged on the microscope under different conditions. (A) INS-1 cells were perfused with Ca²⁺-containing buffer (+[Ca²⁺]_ex) until the baseline was stable before switching to Ca²⁺-free EGTA-containing buffer (-[Ca²⁺]_ex) as indicated in the graphs. 1 µM of the SERCA inhibitor thapsigargin (Tg) was applied under Ca²⁺-free conditions leading to an increase in cytosolic Ca²⁺. Afterwards, extracellular Ca²⁺ was re-added under the presence of Tg. Bars on the right represent the cytosolic Ca²⁺ increase after Ca²⁺ re-addition, mean ± SEM (Control: n=275/9; siPS-1: n=277/9). (B) INS-1 cells were perfused with Ca²⁺-containing buffer (+[Ca²⁺]_ex) and depolarized with 30 mM K⁺-containing buffer. Bars on the right represent the cytosolic Ca²⁺ increase after depolarization with 30 mM K⁺, mean ± SEM (Control: n=273/9; siPS-1: n=281/9).