Halothane activation of ryanodine receptor 2 (RyR2) and its dependencies on cytoplasmic adenosine triphosphate (ATP) and calmodulin (CaM). Concentration dependence of halothane activation of RyR2 open probability (P_o) in the presence and absence of ATP and in the presence of CaM. Experimental conditions and composition of vehicle solution are given in figure 2. Data show the mean ± SD. The curves show Hill fits to the data. Fit parameters and numbers of experiments are given in table 1.