Abstract 18632: Expression and Function of the Ryanodine Receptor Subtype 3 in Cardiac Purkinje Fibers: Potential Target for Selective Treatment of Purkinje Ectopy?
BACKGROUND: Focal “discharges” from the Purkinje network were shown to trigger VTs and VFs in ischemic hearts. In dog model of myocardial infarction, this Purkinje ectopy was attributed to abnormal oscillations of Ca2+ concentration in Purkinje cells (Pcells). The cause of these oscillations is unknown mostly because important features of Ca2+ handling of normal Pcells remain obscure. It was proposed that distinct forms of Ca2+ channels participate to Ca2+ release from endoplasmic reticulum (ER) in canine Pcells, wherein RyR3 was found to co-exist with IP3R and RyR2. Nevertheless, presence of this system of multiple Ca2+ channels has not been explored in other species and the function of this system in Pcells remains unclear. Here, we examined the hypothesis that a specific region of RyR3 Ca2+ release exists in Pcells of large size hearts and forms anatomical and functional coupling between membrane and core ER-Ca2+ releases.
METHODS: Purkinje strands were dissected from hearts of 36 Yucatan swine. Enzymatically dispersed Pcells were loaded with Fluo4. Intracellular Ca2+ dynamics was assessed by 2D confocal imaging (92cells). Function of ER-Ca2+ channels was investigated through effects of selective inhibitors on intracellular Ca2+ transients (65cells). mRNA level was measured in Purkinje fibers by RT-PCR for RyR isoforms 1,2,3 and IP3R (11 animals). Protein expression was characterized by immunofluorescence (34 cells).
RESULTS: Compared to myocardium, 100fold larger RyR3 mRNA level was detected in Purkinje fibers. 3D distribution of RyR3-Ab revealed a concentric RyR3 layer at the cell periphery. Spark rate-pCarelations showed that Ca2+ sensitivity of ER-Ca2+ release at the Pcell periphery was 2fold larger than further in the core. 3 distinct velocities were detected in the typical centripetal Ca2+ propagation of Pcells. RyR3 inhibitor dantrolene (10µM) immediately reduced the Ca2+ release event rate by 50% in the periphery only.
CONCLUSION: RyR3 is a major component of the specific Ca2+ signaling of Pcells of large mammalian heart, suggesting that any RyR3 alteration may cause pro-arrhythmic Ca2+ abnormalities in ischemic heart. Purkinje-specificity of RyR3 highlights a new target for selective treatment of Purkinje-originated dysrhythmia.
- Ion channels
- Excitation-contraction coupling (ECC)
- Heart conduction system
- Ventricular arrhythmia
- © 2012 by American Heart Association, Inc.