J. Neurochem. (2011) 117, 231–243.
Although Zn2+ homeostasis in neurons is tightly regulated and its destabilization has been linked to a number of pathologies including Alzheimer’s disease and ischemic neuronal death, the primary mechanisms affecting intracellular Zn2+ concentration ([Zn2+]i) in neurons exposed to excitotoxic stimuli remain poorly understood. The present work addressed these mechanisms in cultured hippocampal neurons exposed to glutamate and glycine (Glu/Gly). [Zn2+]i and intracellular Ca2+ concentration were monitored simultaneously using FluoZin-3 and Fura-2FF, and intracellular pH (pHi) was studied in parallel experiments using 2′,7′-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein. Glu/Gly applications under Na+-free conditions (Na+ substituted with N-methyl-d-glucamine+) caused Ca2+ influx, pHi drop, and Zn2+ release from intracellular stores. Experimental maneuvers resulting in a pHi increase during Glu/Gly applications, such as stimulation of Na+-dependent pathways of H+ efflux, forcing H+ efflux via gramicidin-formed channels, or increasing extracellular pH counteracted [Zn2+]i elevations. In the absence of Na+, the rate of [Zn2+]i decrease could be correlated with the rate of pHi increase. In the presence of Na+, the rate of [Zn2+]i decrease was about twice as fast as expected from the rate of pHi elevation. The data suggest that Glu/Gly-induced cytosolic acidification promotes [Zn2+]i elevations and that Na+ counteracts the latter by promoting pHi-dependent and pHi-independent mechanisms of cytosolic Zn2+ clearance.