title: In situ Ca2+ dynamics of Purkinje fibers and its interconnection with subjacent ventricular myocytes.
abstract: Purkinje fibers play essential roles in impulse propagation to the ventricles, and their functional impairment can become arrhythmogenic. However, little is known about precise spatiotemporal pattern(s) of interconnection between Purkinje-fiber network and the underlying ventricular myocardium within the heart. To address this issue, we simultaneously visualized intracellular Ca(2+) dynamics at Purkinje fibers and subjacent ventricular myocytes in Langendorff-perfused rat hearts using multi-pinhole type, rapid-scanning confocal microscopy. Under recording of electrocardiogram at room temperature spatiotemporal changes in fluo3-fluorescence intensity were visualized on the subendocardial region of the right-ventricular septum. Staining of the heart with either fluo3, acetylthiocholine iodide (ATCHI), or di-4-ANEPPS revealed characteristic structures of Purkinje fibers. During sinus rhythm (about 60 bpm) or atrial pacing (up to 3 Hz) each Purkinje-fiber exhibited spatiotemporally synchronous Ca(2+) transients nearly simultaneously to ventricular excitation. Ca(2+) transients in individual fibers were still synchronized within the Purkinje-fiber network not only under high-K(+) (8 mM) perfusion-induced Purkinje-to-ventricular (P-V) conduction delay, but also under unidirectional, orthodromic P-V block produced by 10-mM K(+) perfusion. While spontaneous, asynchronous intracellular Ca(2+) waves were identified in injured fibers of Purkinje network locally, surrounding fibers still exhibited Ca(2+) transients synchronously to ventricular excitation. In summary, these results are the first demonstration of intracellular Ca(2+) dynamics in the Purkinje-fiber network in situ. The synchronous Ca(2+) transients, preserved even under P-V conduction disturbances or under emergence of Ca(2+) waves, imply a syncytial role of Purkinje fibers as a specialized conduction system, whereas unidirectional block at P-V junctions indicates a substrate for reentrant arrhythmias.
authors.affiliation: Department of Pathology and Cell Regulation, Kyoto Prefectural University of Medicine, Kamigyo-Ku, Kyoto 602-8566, Japan.
authors.forename: Tetsu
authors.initials: T
authors.lastname: Hamamoto
authors.forename: Hideo
authors.initials: H
authors.lastname: Tanaka
authors.forename: Hiroki
authors.initials: H
authors.lastname: Mani
authors.forename: Takuji
authors.initials: T
authors.lastname: Tanabe
authors.forename: Katsuji
authors.initials: K
authors.lastname: Fujiwara
authors.forename: Takuo
authors.initials: T
authors.lastname: Nakagami
authors.forename: Minoru
authors.initials: M
authors.lastname: Horie
authors.forename: Masahito
authors.initials: M
authors.lastname: Oyamada
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Takamatsu
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D004562:Electrocardiography; D004699:Endocardium / Q000378:metabolism; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D018613:Microscopy, Confocal; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011690:Purkinje Fibers / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002413:Cations, Divalent; D002118:Calcium