title: Ca(2+) release events in cardiac myocytes up close: insights from fast confocal imaging.
abstract: The spatio-temporal properties of Ca(2+) transients during excitation-contraction coupling and elementary Ca(2+) release events (Ca(2+) sparks) were studied in atrial and ventricular myocytes with ultra-fast confocal microscopy using a Zeiss LSM 5 LIVE system that allows sampling rates of up to 60 kHz. Ca(2+) sparks which originated from subsarcolemmal junctional sarcoplasmic reticulum (j-SR) release sites in atrial myocytes were anisotropic and elongated in the longitudinal direction of the cell. Ca(2+) sparks in atrial cells originating from non-junctional SR and in ventricular myocytes were symmetrical. Ca(2+) spark recording in line scan mode at 40,000 lines/s uncovered step-like increases of [Ca(2+)]i. 2-D imaging of Ca(2+) transients revealed an asynchronous activation of release sites and allowed the sequential recording of Ca(2+) entry through surface membrane Ca(2+) channels and subsequent activation of Ca(2+)-induced Ca(2+) release. With a latency of 2.5 ms after application of an electrical stimulus, Ca(2+) entry could be detected that was followed by SR Ca(2+) release after an additional 3 ms delay. Maximum Ca(2+) release was observed 4 ms after the beginning of release. The timing of Ca(2+) entry and release was confirmed by simultaneous [Ca(2+)]i and membrane current measurements using the whole cell voltage-clamp technique. In atrial cells activation of discrete individual release sites of the j-SR led to spatially restricted Ca(2+) release events that fused into a peripheral ring of elevated [Ca(2+)]i that subsequently propagated in a wave-like fashion towards the center of the cell. In ventricular myocytes asynchronous Ca(2+) release signals from discrete sites with no preferential subcellular location preceded the whole-cell Ca(2+) transient. In summary, ultra-fast confocal imaging allows investigation of Ca(2+) signals with a time resolution similar to patch clamp technique, however in a less invasive fashion.
authors: Deptartment of General Physiology of the Nervous System, A. A. Bogomoletz Institute of Physiology, Kiev, Ukraine.
authors: Vyacheslav M
authors: VM
authors: Shkryl
authors: Lothar A
authors: LA
authors: Blatter
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002415:Cats; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000502:physiology
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium
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