title: Polymorphism of Ca2+ sparks evoked from in-focus Ca2+ release units in cardiac myocytes.
abstract: Ca2+ sparks are the elementary release events in many types of cells. Here we present a morphometric analysis of Ca2+ sparks (i.e., amplitude and kinetic parameters) using an approach that minimizes the confounding factor of the detection of out-of-focus events. By activation and visualization of Ca2+ sparks from Ca2+ release units under loose-seal patch-clamp conditions, we found that the amplitude and rising rate of in-focus sparks exhibited a broad modal distribution, whereas spark rise time and spatial width appeared to be stereotyped. Spark morphometrics were constant irrespective of the latency of spark production and the time-dependent L-type Ca2+ channel activation. Polymorphism of Ca2+ sparks in terms of variable amplitude and rising rate was evident for events from the same release units, and intra- and interrelease unit variability contributed equally to the overall variability. The rising rate, a reporter of the underlying Ca2+ release flux, displayed a strong positive correlation with spark amplitude, but a negative correlation with spark rise time, an index of Ca2+ release duration. On the basis of Ca2+ spark morphometrics measured here, we suggested a model in which cohorts of variable number of ryanodine receptors are activated in the genesis of Ca2+ sparks, and the ensuing negative feedback overrides the regenerative Ca2+-induced Ca2+ release to extinguish the ongoing Ca2+ spark.
authors.affiliation: Department of Physiology, Medical School of Xi'an Jiaotong University, Xi'an 710061, China.
authors.forename: Jian-Xin
authors.initials: JX
authors.lastname: Shen
authors.forename: ShiQiang
authors.initials: S
authors.lastname: Wang
authors.forename: Long-Sheng
authors.initials: LS
authors.lastname: Song
authors.forename: Taizhen
authors.initials: T
authors.lastname: Han
authors.forename: Heping
authors.initials: H
authors.lastname: Cheng
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D018613:Microscopy, Confocal / Q000379:methods*; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods*; D011110:Polymorphism, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
chemical_list: D002118:Calcium