Figure 5. Carbachol-activated currents in HEK cells expressing the Lck-STIM1-C construct. (A) Mean (± SE) carbachol-activated Ca²⁺ currents measured at -80 mV in HEK cells expressing the m3 muscarinic receptor. Shown are the total agonist-activated currents (gray), and the same currents recorded in cells after depletion of ER Ca²⁺ stores by intracellular adenophostin A (black) in untransfected control cells (control) and in STIM1 siRNA-treated cells expressing the Lck-STIM1-C construct. (B) Mean (± SE) I/V curves for the total agonist-activated currents (gray), and adenophostin-insensitive currents (black) in control cells and (C) the same for the Lck-STIM1-C expressing cells (see text for details). (D) Mean (± SE) curves comparing the activation kinetics of carbachol-activated currents in m3-HEK cells expressing the Lck-STIM1-C construct compared with those in wild-type m3-HEK cells. Total currents were normalized to their final maximal values to allow direct comparison of their respective rates of activation following addition of carbachol (10 µM) at time zero.