Fig. 3. Effect of halothane on inositol triphosphate (IP3) receptor channels in intact (A ) and β-escin–permeabilized (B ) airway smooth muscle (ASM) cells. During conditions of blocked Ca2+influx and efflux, halothane induced a transient intracellular Ca2+concentration ([Ca2+]i) response even when IP3receptor channels were blocked by a membrane permeant inhibitor, Xestospongin D (XeD). These data indicate that halothane increases sarcoplasmic reticulum Ca2+release also through ryanodine receptor (RyR) channels. The decrease in the [Ca2+]iresponse to halothane during these conditions is consistent with figure 3, indicating the IP3receptor component. Amplitude bar for (A ) only. MAC = minimum alveolar concentration.