Amplitude Distribution of Calcium Sparks in Confocal Images: Theory and Studies with an Automatic Detection Method

Abstract

Determination of the calcium spark amplitude distribution is of critical importance for understanding the nature of elementary calcium release events in striated muscle. In the present study we show, on general theoretical grounds, that calcium sparks, as observed in confocal line scan images, should have a nonmodal, monotonic decreasing amplitude distribution, regardless of whether the underlying events are stereotyped. To test this prediction we developed, implemented, and verified an automated computer algorithm for objective detection and measurement of calcium sparks in raw image data. When the sensitivity and reliability of the algorithm were set appropriately, we observed highly left-skewed or monotonic decreasing amplitude distributions in skeletal muscle cells and cardiomyocytes, confirming the theoretical predictions. The previously reported modal or Gaussian distributions of sparks detected by eye must therefore be the result of subjective detection bias against small amplitude events. In addition, we discuss possible situations when a modal distribution might be observed.

Improved spark and ember detection using stationary wavelet transforms

“…The implementation of the traditional method is a modified version of the algorithm given in a previous work (Cheng et al 1999). In brief, the original F(x,t) image is filtered with a 3x3 median filter.…”

“…First, the background was approximated by a generated noise with Gaussian distribution (e.g. Cheng et al 1999;Wegner et al 2006). This is a good approximation for images with low levels of shot noise.…”

“…The goal of these algorithms is to detect and then isolate the area of each event from the noisy background, and, finally, to extract the characteristic parameters of the events. Most of these methods are based on a double threshold algorithm (this will be referred to as the conventional method) proposed by Cheng et al (1999). Modified versions of the algorithm were used in several studies (Ríos et al 2001;Zhou et al 2003;Sebille et al 2005;Picht et al 2007).…”

Homer Protein Increases Activation of Ca2+ Sparks in Permeabilized Skeletal Muscle

“…Line scan images were computer processed to automatically identify and store spark locations using a relative threshold algorithm as described by Cheng et al (16) and analyzed as previously described by our laboratory (13,17). Identified Ca 2ϩ sparks were analyzed for frequency of occurrence (events⅐sarcomere Ϫ1 ⅐sec Ϫ1 ), and for the following spatio-temporal properties: rise time (10 -90% ⌬F/F; ms), full-duration at half-maximal ⌬F/F (FDHM; ms), full-width at halfmaximal ⌬F/F (FWHM; m) and amplitude (peak ⌬F/F).…”

“…is well known that RyR-dependent SR Ca 2ϩ release is modulated by endogenous ions such as Ca 2ϩ and Mg 2ϩ (16,24,25). In addition, RyR-dependent Ca 2ϩ release is also modulated by regulatory proteins such as calmodulin (26,27) and FKBP12 (28,29), which associate at distinct binding sites on the RyR (30,31).…”