Analysis of Localized Calcium Alteration During Neural Cell Death

Abstract

Fluctuations in intracellular calcium ion (Ca2+i) levels are believed to participate in a myriad of physiological and pathological intracellular events. In an attempt to investigate localized alterations in Ca2+i dynamics in a cell-based neurodegeneration model, we used Fura-2/AM dye to monitor Ca2+i ion levels in the human SH-SY5Y neuroblastoma cells induced to undergo apoptosis with 500 nM staurosporine (STS) over a 24 h period. Using rapid illumination frequency at 5 Hz per 340/380 nm excitation wavelength pair, streaming image acquisition and analysis of 12 very small regions of interest (ROI) of ∼86.5 μm2 in either peri-nuclear (PN) or distal (DST) cytoplasmic locations, we captured micro-regional signals (“Ca2+i ripples”) at selected eight time points that were analyzed for dynamic changes in peak Ca2+i amplitudes and frequencies across both STS exposure times and CCh treatment with standard methods consisting of nonlinear curve-fitting and fast Fourier transform, respectively, and with a novel method of recurrence quantification analysis. Their results, although at times mixed or conflicting, showed that there may indeed be alterations in local Ca2+i signaling/dynamic which are biologically valid and sometimes differ from the global Ca2+i signaling/dynamic of whole cytoplasms. I propose, then, that, at least for intrinsic apoptosis, an early activation of caspases leads to cleavages of increasingly more IP3 receptors and sarco-/endoplasmic reticulum Ca2+ ATPase of ER which may enhance Ca2+i release by the former and inhibit uptake by the latter. Ultimately, this results in the accumulation of the ion that starts locally and heterogeneously until spreading by waves and becoming more apparent at the whole cytoplasmic scale.