Fig. 1. Halothane opens background K+channels and hyperpolarizes specific neurons. (A ) Anesthetic concentrations of halothane reversibly block the endogenous firing activity of a pacemaker neuron in Lymnaea . (Adapted with permission from Franks and Lieb. 9) (B ) Current–voltage relations for a typical Lymnaea isolated anesthetic-sensitive neuron in the presence of 1.4 mm halothane. The current–voltage relations in control (before the addition of halothane) and after washout are illustrated. (Adapted with permission from Lopes et al. 11)