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. Accordingly, endogenous factors that alter the operation of these conductances may have profound effects on neuronal function. We now report that several G-protein-modulated ionic conductances in hippocampal neurons are very much altered when Cl- is the predominant anion in the recording electrode. We used both sharp-electrode and whole-cell techniques in rat hippocampal slices to determine whether hippocampal CA1 pyramidal cell properties are altered by KCl-filled, as compared with KCH3SO3- or K-gluconate-filled, electrodes. We studied the effects of the anions on synaptically evoked GABAB responses and baclofen- and serotonin-induced currents as well as on a voltage-activated cation current, Ih. High intracellular concentrations of chloride ([Cl-]i) depressed all the responses without altering resting cell properties. Intermediate [Cl-]i reduced baclofen-induced currents as well as Ih in a dose-dependent manner. In KCH3SO3-filled cells, equimolar substitution of GTPgammaS for Tris-GTP results in activation of a K+ conductance that hyperpolarizes cells and lowers their input resistance. These effects of GTPgammaS were blocked in KCl-filled cells. In view of the tight coupling between the G-protein and activation of the GABAB-activated K+ conductance, the effect of Cl- ions is likely to be exerted either on the G-protein or the K+ channel itself. We observed substantial effects of Cli- at concentrations that are believed to exist during development in the CNS as well as during pathological conditions, 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.