Figure 3. Concentration-response curves generated by guanosine 5'-O-(3-thiotriphosphate)(GTP gamma S)(0.001–31.6 micro Meter; n = 5) at a constant submaximal [Ca²+]ⁱof 0.1 micro Meter (A) and by phorbol 12,13-dibutyrate (PDBu)(0.001–3 micro Meter; n = 5) at a constant submaximal [Ca²+]ⁱof 0.3 micro Meter (B) in the absence (control) and presence of 0.97 +/- 0.13 mM halothane in beta-escin-permeabilized 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.