Calcium transient activity in cultured murine neural crest cells is regulated at the IP3 receptor

In a previous study we have shown that cultured neural crest cells exhibit spontaneous calcium transients and that these events are required for neurogenesis. In this study, we examine the mechanism that generates these calcium transients. Extracellular Ca2+ modulates calcium transient activity. Lanthanum (La3+), a general calcium channel antagonist and zero extracellular Ca2+, reduces the percentage of cells exhibiting calcium transients (26.2 and 40.5%, respectively) and decreases calcium spiking frequency (4.5 to 1.0 and 2.5 to 1.0 spikes/30 min, respectively). Intracellular calcium stores also contribute to the generation of calcium transients. Depleting the calcium stores of the endoplasmic reticulum (ER) reduces the percentage of active cells (15.7%) and calcium spiking frequency (2.8 to 1.5 spikes/30 min). Ryanodine (100 mu M), which blocks calcium release regulated by the ryanodine receptor (RyR), had no effect on calcium transient activity. Blocking inositol 1,4,5-triphosphate receptor (IP3R)-dependent calcium release, with elevated extracellular Mg2+ (20 mM), abolished calcium transient activity. Mg2+ did not block caffeine-sensitive calcium release (RyR-dependent) or voltage dependent calcium channels. Mg2+ also suppressed thimerosal-induced calcium oscillations (IP3R-dependent). Small increases in the intracellular calcium concentration ([Ca2+](i)), increases the percentage of active cells and the calcium spiking frequency, while larger increases in [Ca2+](i) block the transients. Reducing intracellular IP3 levels reduces the percentage of active cells and the calcium spiking frequency. We conclude that the mechanism for generating spontaneous calcium transients in cultured neural crest cells fits the model for IP3R-dependent calcium excitability of the ER. (C) 2000 Elsevier Science B.V. All rights reserved.