Fig. 3. Activation of the G-protein-coupled M5 muscarinic receptor results in stimulation of Ba²⁺ entry in wild-type but not in IP₃R-KO DT40 cells. Ba²⁺ influx was measured in single Fura-2-loaded wild-type (WTDT40) or IP₃R-KO (dotted line) DT40 cells transfected with the human M5 muscarinic receptor. The cells were maintained in nominally Ca²⁺-free medium, exposed to 100 µM carbachol, and then Ba²⁺ (10 mM) was added where indicated. The relatively higher ratio values in this experiment are due to the use of a different Ca²⁺ measuring system; in this series, a photon counting system was used, while in the other series, an imaging system was used. Representative traces from three independent experiments are shown.