Inhibition of glutamate‐induced delayed calcium deregulation by 2‐APB and La3+ in cultured cortical neurones

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Abstract
Exposure of neurones in culture to excitotoxic levels of glutamate results in an initial transient spike in [Ca2+]i followed by a delayed, irreversible [Ca2+]i rise governed by rapid kinetics, with Ca2+ originating from the extracellular medium. The molecular mechanism responsible for the secondary Ca2+ rise is unknown. Here, we report that the delayed Ca2+ entry in cortical neurones is diminished by 2‐aminoethoxydiphenyl borate (2‐APB: IC50 = 62 ± 9 µm) and La3+ (IC50 = 7.2 ± 3 µm), both known to inhibit transient receptor potential (TRP) and store‐operated Ca2+ (SOC) channels. Application of thapsigargin, however, failed to exacerbate the delayed Ca2+ deregulation, arguing against a store depletion event as the stimulus for induction of the secondary [Ca2+]i rise. In addition, these neurones did not exhibit SOC entry. Unexpectedly, application of ryanodine or caffeine significantly inhibited glutamate‐induced delayed Ca2+ deregulation. In basal Ca2+ entry experiments, La3+ and 2‐APB modulated the rapid rise in [Ca2+]i caused by exposure of neurones to Ca2+ after pre‐incubating in a calcium‐free medium. This basal Ca2+ influx was mitigated by extracellular Mg2+ but not aggravated by thapsigargin, ryanodine or caffeine. These results indicate that 2‐APB and La3+ influence non‐store‐operated Ca2+ influx in cortical neurones and that this route of Ca2+ entry is involved in glutamate‐induced delayed Ca2+ deregulation.