HIGH INTRACELLULAR CL- CONCENTRATIONS DEPRESS G-PROTEIN-MODULATED IONIC CONDUCTANCES

Numerous G-protein-modulated ionic conductances are present in central neurons and play major roles in regulating neuronal excitability. Acc ordingly, endogenous factors that alter the operation of these conduct ances may have profound effects on neuronal function. We now report th at several G-protein-modulated ionic conductances in hippocampal neuro ns are very much altered when Cl- is the predominant anion in the reco rding electrode. We used both sharp-electrode and whole-cell technique s in rat hippocampal slices to determine whether hippocampal CA1 pyram idal cell properties are altered by KCl-filled, as compared with KCH3S O3 or K-gluconate-filled, electrodes. We studied the effects of the an ions on synaptically evoked GABA(B) responses and baclofen-and seroton in-induced currents as well as on a voltage-activated cation current, I-h. High intracellular concentrations of chloride ([Cl-](i)) depresse d all the responses without altering resting cell properties. Intermed iate [Cl-](i) reduced baclofen-induced currents rents as well as I-h i n a dose-dependent manner. In KCH3SO3-filled cells, equimolar substitu tion of GTP gamma S for Tris-GTP results in activation of a K+ conduct ance that hyperpolarizes cells and lowers their input resistance. Thes e effects of GTP gamma S were blocked in KCl-filled cells. In view of the tight coupling between the G-protein and activation of the GABA(B) -activated K+ conductance, the effect of Cl- ions is likely to be exer ted either on the G-protein or the K+ channel itself. We observed subs tantial effects of Cl-i(-) at concentrations that are believed to exis t during development in the CNS as well as during pathological conditi ons, such as spreading depression. Thus, the results we describe must be taken into consideration during such physiological and pathological conditions as well as in experimental studies of G-protein-modulated conductances.