Electrophysiology of the GABAergic synapses

GABA is the most widely distributed inhibitory transmitter in the brain, and it acts commonly by augmenting chloride permeability. When resting membrane potential (Vm) is equal to chloride equilibrium potential (EC1) GABA tends to keep Vm to its resting value. In some synapses, a pump carries chloride actively out of the cell and EC1 is different from Vm. An increased permeability leads to a hyperpolarization. In presynaptic inhibition a chloride pump brings chloride ions actively inside the cell and an increased permeability leads to a depolarization. GABAA receptors are associated with chloride channels, whereas GABAB receptors cause a selective decrease of a voltage sensitive calcium channels which operates at synaptic terminals.