Cooperative and stochastic calcium releases from multiple calcium puff sites generate calcium microdomains in intact HeLa cells

Abstract

Ca2+ microdomains or locally restricted Ca2+ increases in the cell have recently been reported to regulate many essential physiological events. Ca2+ increases through the inositol 1,4,5-trisphosphate(IP3)receptor(IP3R)/Ca2+ release channels contribute to the formation of a class of such Ca2+ microdomains, which were often observed and referred to as Ca2+ puffs in their isolated states. In this report, we visualized IP3-evoked Ca2+ microdomains in histamine-stimulated intact HeLa cells using a total internal reflection fluorescence microscope, and quantitatively characterized the spatial profile by fitting recorded images to a two-dimensional Gaussian distribution. Ca2+ concentration profiles were marginally spatially anisotropic, with the size increasing linearly even after the amplitude began to decline. We found the event centroid drifted with an apparent diffusion coefficient of 4.20 ± 0.50 μm2/s, which is significantly larger than those estimated for IP3Rs. The sites of maximal Ca2+ increase, rather than initiation or termination sites, were detected repeatedly at the same location. These results indicate that Ca2+ microdomains in intact HeLa cell are generated from spatially distributed multiple IP3R clusters or Ca2+ puff sites, rather than a single IP3R cluster reported in cells loaded with Ca 2+ buffers. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc.