Abstract
Cellular Ca(2+) signals are often constrained to cytosolic micro- or nano-domains where stochastic openings of Ca(2+) channels cause large fluctuations in local Ca(2+) concentration (Ca(2+) 'noise'). With the advent of TIRF microscopy to image the fluorescence of Ca(2+)-sensitive probes from attoliter volumes it has become possible to directly monitor these signals, which closely track the gating of plasmalemmal and ER Ca(2+)-permeable channels. Nevertheless, it is likely that many physiologically important Ca(2+) signals are too small to resolve as discrete events in fluorescence recordings. By analogy with noise analysis of electrophysiological data, we explore here the use of statistical approaches to detect and analyze such Ca(2+) noise in images obtained using Ca(2+)-sensitive indicator dyes. We describe two techniques - power spectrum analysis and spatio-temporal correlation - and demonstrate that both effectively identify discrete, spatially localized calcium release events (Ca(2+) puffs). Moreover, we show they are able to detect localized noise fluctuations in a case where discrete events cannot directly be resolved.