Figure 4. Halothane reversibly inhibits thromboxane A2(TXA2) receptor functioning. (A) Examples of ICl(Ca) induced by U-46619 (10 sup -6 M) in oocytes expressing TXA2receptors. The charge movement in response to U-46619 is 8.6 micro C. Halothane concentrations are indicated and correspond to 1, 2, and 3 minimum alveolar concentrations, resulting in charge movements of 3.9, 1.7, and 0.8 micro C, respectively. (B) Halothane inhibits ICl(Ca) responses to TXA sub 2 agonist U-46619 (10 sup -6 M) in a concentration-dependent manner. Curve fitting using the Hill equation revealed a half-maximal inhibitory concentration (IC50) of 0.47 +/- 0.05 mM (0.83%) and a Hill coefficient of 1.6 +/- 0.2. (C) ICl(Ca) induced by U-46619 (10 sup -6 M) to determine the reversibility of halothane inhibition. Three consecutive measurement were made in each oocyte. The first bar represents control measurements (9.36 +/- 1.86 micro C). The second bar shows the inhibitory effect of 1.07 mM halothane (2.5%). ICl(Ca) was reduced to 17% of control (1.59 +/- 0.86 micro C). The third bar shows recovery after 10 min of perfusion with Tyrode's solution without anesthetic (9.58 +/- 1.98 micro C).