Modulation of miniature inhibitory postsynaptic currents by isoflurane in rat dissociated neurons with glycinergic synaptic boutons.

The effects of a volatile anesthetic, isoflurane, on glycinergic miniature inhibitory postsynaptic currents (IPSCs) were investigated in mechanically dissociated rat trigeminal nucleus neurons with intact glycinergic interneuronal presynaptic nerve terminals. The nystatin-perforated patch recording configuration was used to record the miniature IPSCs under voltage-clamp conditions. Isoflurane shifted in a parallel fashion the glycine (Gly) concentration-response curve of enzymatically dissociated neurons to the left without changing the maximum response. Isoflurane reversibly increased the frequency of the miniature IPSCs and prolonged the decay time constant without affecting the mean amplitude. The increase in the frequency of miniature IPSCs in the presence of isoflurane was also observed in Ca(2+)-free external solution. Thapsigargin prohibited the facilitatory effect of isoflurane on the miniature IPSC frequency. It is concluded that isoflurane increases the Ca(2+) concentration in the glycinergic presynaptic nerve terminal by enhancing the release and/or suppressing the uptake of Ca(2+) into stores.