Estimate of the chloride concentration in a central glutamatergic terminal: A gramicidin perforated-patch study on the calyx of held

The function of presynaptic terminals is regulated by intracellular Cl ^-, the levels of which modify vesicular endocytosis and transmitter refilling and mediate the effects of presynaptic ligand-gated Cl^- channels. Nevertheless, the concentration of Cl^- in a central nerve terminal is unknown, and it is unclear whether terminals can regulate Cl ^- independently of the soma. Using perforated-patch recording in a mammalian synapse, we found that terminals accumulate Cl^- up to 21mM, between four and five times higher than in their parent cell bodies. Changing [Cl^-] did not alter vesicular glutamate content in intact terminals, unlike in vitro experiments. Thus, glutamatergic terminals maintain an elevated Cl^- concentration without compromising synaptic transmission.