Author + information
- Received June 1, 2020
- Revision received June 19, 2020
- Accepted June 24, 2020
- Published online August 17, 2020.
- Rostislav Bychkov, PhD,
- Magdalena Juhaszova, PhD,
- Kenta Tsutsui, MD, PhD,
- Christopher Coletta, MS,
- Michael D. Stern, MD,
- Victor A. Maltsev, PhD and
- Edward G. Lakatta, MD∗ ()
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
- ↵∗Address for correspondence:
Dr. Edward G. Lakatta, Laboratory of Cardiovascular Science, NIA/NIH, Biomedical Research Center, 251 Bayview Boulevard, Baltimore, Maryland 21224.
Objectives This study sought to identify subcellular Ca2+ signals within and among cells comprising the sinoatrial node (SAN) tissue.
Background The current paradigm of SAN impulse generation: 1) is that full-scale action potentials (APs) of a common frequency are initiated at 1 site and are conducted within the SAN along smooth isochrones; and 2) does not feature fine details of Ca2+ signaling present in isolated SAN cells, in which small subcellular, subthreshold local Ca2+ releases (LCRs) self-organize to generate cell-wide APs.
Methods Immunolabeling was combined with a novel technique to detect the occurrence of LCRs and AP-induced Ca2+ transients (APCTs) in individual pixels (chronopix) across the entire mouse SAN images.
Results At high magnification, Ca2+ signals appeared markedly heterogeneous in space, amplitude, frequency, and phase among cells comprising an HCN4+/CX43− cell meshwork. The signaling exhibited several distinguishable patterns of LCR/APCT interactions within and among cells. Rhythmic APCTs that were apparently conducted within the meshwork were transferred to a truly conducting HCN4−/CX43+ network of striated cells via narrow functional interfaces where different cell types intertwine, that is, the SAN anatomic/functional unit. At low magnification, the earliest APCT of each cycle occurred within a small area of the HCN4 meshwork, and subsequent APCT appearance throughout SAN pixels was discontinuous and asynchronous.
Conclusions The study has discovered a novel, microscopic Ca2+ signaling paradigm of SAN operation that has escaped detection using low-resolution, macroscopic tissue isochrones employed in prior studies: synchronized APs emerge from heterogeneous subcellular subthreshold Ca2+ signals, resembling multiscale complex processes of impulse generation within clusters of neurons in neuronal networks.
This work was supported by the Intramural Research Program of the National Institutes of Health, National Institute on Aging. The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
The authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
- Received June 1, 2020.
- Revision received June 19, 2020.
- Accepted June 24, 2020.