Fig. 5.

Dorsal raphe neurons express a pH- and halothane-sensitive K⁺ conductance with properties of TASK channels. Dorsal raphe neurons were recorded under whole-cell voltage clamp in slices of rat midbrain. A, As expected for serotonergic dorsal raphe neurons, 5-HT (100 μm) evoked an outward shift in membrane current at holding potential of −60 mV. Extracellular acidification (from pH 7.3 to pH 6.0) evoked an inward shift in holding current. After wash into control pH 7.3 solution, halothane (1.25 mm) evoked an outward shift in current, and, in the presence of halothane, the current shift induced by reacidifying the bath solution was enhanced in amplitude.B, Examples of current responses to incrementing voltage steps (Δ −10 mV) from −60 mV that were used to constructI–V relationships (taken at times corresponding to those indicated in A); note that currents were essentially completely activated before the end of the capacitive transient (i.e., they were instantaneous) and were non-inactivating.C, Averaged I–V relationships of pH-sensitive currents (diamonds) were derived by subtracting currents recorded in the acidified bath (b) from those obtained under control conditions (a); the pH-sensitive current in the presence of halothane (squares) was likewise derived by subtracting currents recorded before (c) and after (d) bath acidification during continued exposure to halothane (±SEM; n = 14). D, Subtracting pH-sensitive currents obtained in the presence of halothane from those obtained under control conditions yielded the averagedI–V relationship of the joint halothane- and pH-sensitive component of dorsal raphe current (±SEM;n = 14). Those I–V data were well fitted to the GHK equation, consistent with involvement of an open-rectifier TASK-like current.