title: Pacing-induced non-uniform ca(2+) dynamics in rat atria revealed by rapid-scanning confocal microscopy.
abstract: Intracellular Ca(2+) ([Ca(2+)]i) dynamics in isolated myocytes differ between the atria and ventricles due to the distinct t-tubular distributions. Although cellular aspects of ventricular [Ca(2+)]i dynamics in the heart have been extensively studied, little is known about those of atrial myocytes in situ. Here we visualized precise [Ca(2+)]i dynamics of atrial myocytes in Langendorff-perfused rat hearts by rapid-scanning confocal microscopy. Of 16 fluo-4-loaded hearts imaged during pacing up to 4-Hz, five hearts showed spatially uniform Ca(2+) transients on systole among individual cells, whereas no discernible [Ca(2+)]i elevation developed during diastole. In contrast, the remaining hearts showed non-uniform [Ca(2+)]i dynamics within and among the cells especially under high-frequency (4 Hz) excitation, where subcellular cluster-like [Ca(2+)]i rises or wave-like [Ca(2+)]i propagation occurred on excitation. Such [Ca(2+)]i inhomogeneity was more pronounced at high-frequency pacing, showing beat-to-beat Ca(2+) transient alternans. Despite such non-uniform dynamics, cessation of burst pacing of the atria was not followed by emergence of spontaneous Ca(2+) waves, indicating minor Ca(2+)-releasing potentials of the sarcoplasmic reticulum (SR). In summary, rat atria display a propensity to show non-uniform [Ca(2+)]i dynamics on systole due to impaired Ca(2+)-release from the SR and paucity of t-tubules. Our results provide an important basis for understanding atrial pathophysiology.
authors.affiliation: Department of Pathology and Cell Regulation, Kyoto Prefectural University of Medicine, Graduate School of Medical Science , Kyoto, 602-8566, Japan.
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Department of Pathology and Cell Regulation, Kyoto Prefectural University of Medicine, Graduate School of Medical Science , Kyoto, 602-8566, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Department of Pathology and Cell Regulation, Kyoto Prefectural University of Medicine, Graduate School of Medical Science , Kyoto, 602-8566, Japan ; Department of Pathology, National Cerebral and Cardiovascular Center, Suita, Osaka 565-8565, Japan.
authors.forename: Taka-Aki
authors.initials: TA
authors.lastname: Matsuyama
authors.affiliation: Department of Pathology and Cell Regulation, Kyoto Prefectural University of Medicine, Graduate School of Medical Science , Kyoto, 602-8566, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Yamaoka
authors.affiliation: Department of Pathology and Cell Regulation, Kyoto Prefectural University of Medicine, Graduate School of Medical Science , Kyoto, 602-8566, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Takamatsu
keywords: Ca2+ alternans; Ca2+ transient; atrium; rat; transverse tubule