Fig. 4. Gs-GPCRs use two separable calcium release mechanisms, both of which depend on prior Gq priming.

Calcium mobilization in HEK293 and HEK-∆AC3/6 cells following the two consecutive addition protocol. Images show representative real-time Ca²⁺ recordings, concentration-effect curves derived therefrom, and bar chart quantification for the enhancement of cytosolic Ca²⁺ by the calcium ionophore A23187 (5 µM). a, b Ca²⁺ responses in HEK293 cells in the absence or presence of (a) 10 µM PKA-inhibitor (PKI14-22) or (b) 25 µM EPAC-inhibitor (HJC0197) after priming with 100 µM ATP and followed by addition of Iso. c, d Fsk-Ca²⁺ in HEK293 cells with and without prior Gq priming. e, f Iso- and Fsk-induced cytosolic Ca²⁺ increase in HEK293 (e) and HEK-∆AC3/6 cells (f) after ATP priming. Representative calcium traces are means + SEM. Quantified data are mean values ± SEM for n independent biological experiments (a–c: n = 3; d: n = 4; e: Iso n = 4, Fsk n = 9; f: n = 4), each performed in duplicate. Source data are provided as a Source Data file.