Secondary Ca2+ overload indicates early neuronal injury which precedes staining with viability indicators.

Spinal neurons, lethally challenged with excitatory amino acids (EAAs) or with high-K+, underwent a biphasic rise in free intracellular calcium concentration ([Ca2+]i). In contrast to the initial rise in [Ca2+]i which recovered, the secondary, irreversible [Ca2+]i increase was unaffected by antagonists of EAA receptors or Ca2+ channels. Also, it correlated highly with cell death, but preceded vital staining with trypan blue and ethidium homodimer, reflecting damaged cellular Ca2+ regulation rather than plasma membrane leakiness. Our findings suggest that delayed Ca2+ overload is the end-product rather than the cause of Ca(2+)-triggered neurotoxic processes.