Figure 2. Free Ca2+ concentration-response curves (0.01–10 micro Meter) generated by free Ca2+ alone (Ca2+ control) and during activation of GTP-binding proteins with 3 micro Meter guanosine 5'O-(3-thiotriphosphate)(GTP gamma S; n = 6)(A) and protein kinase C with 1 micro Meter phorbol 12,13-dibutyrate (PDBu; n = 6)(B) in the presence and absence of 0.99 +/- 0.04 mM halothane (GTP gamma S + H; PDBu + H, respectively) in beta-escin-permeabilized canine tracheal smooth muscle strips. Values are normalized as a percentage of maximal force induced by 10 micro Meter free Ca2+ determined in the same tissues. Data are expressed as mean values +/- SD.