TY - JOUR
T1 - Heterogeneity of calcium clock functions in dormant, dysrhythmically and rhythmically firing single pacemaker cells isolated from SA node
AU - Kim, Mary S.
AU - Maltsev, Alexander V.
AU - Monfredi, Oliver
AU - Maltseva, Larissa A.
AU - Wirth, Ashley
AU - Florio, Maria Cristina
AU - Tsutsui, Kenta
AU - Riordon, Daniel R.
AU - Parsons, Sean P.
AU - Tagirova, Syevda
AU - Ziman, Bruce D.
AU - Stern, Michael D.
AU - Lakatta, Edward G.
AU - Maltsev, Victor A.
N1 - Funding Information:
This research was supported by the Intramural Research Program of the National Institutes of Health, National Institute on Aging . Sean Parsons was supported the Canadian Institutes of Health Research ( MOP12874 ) and the Natural Sciences and Engineering Research Council ( 386877 ). O. Monfredi was supported by a clinical lectureship from the National Institute for Health Research, United Kingdom . K. Tsutsui was supported by Japan Society for the Promotion of Science Research Fellowship for Japanese Biomedical and Behavioral Researchers at the National Institutes of Health. We acknowledge the statistical support of Dr. Christopher Morrell.
Publisher Copyright:
© 2018
PY - 2018/9
Y1 - 2018/9
N2 - Current understanding of how cardiac pacemaker cells operate is based mainly on studies in isolated single sinoatrial node cells (SANC), specifically those that rhythmically fire action potentials similar to the in vivo behavior of the intact sinoatrial node. However, only a small fraction of SANC exhibit rhythmic firing after isolation. Other SANC behaviors have not been studied. Here, for the first time, we studied all single cells isolated from the sinoatrial node of the guinea pig, including traditionally studied rhythmically firing cells (‘rhythmic SANC’), dysrhythmically firing cells (‘dysrhythmic SANC’) and cells without any apparent spontaneous firing activity (‘dormant SANC’). Action potential-induced cytosolic Ca 2+ transients and spontaneous local Ca 2+ releases (LCRs) were measured with a 2D camera. LCRs were present not only in rhythmically firing SANC, but also in dormant and dysrhythmic SANC. While rhythmic SANC were characterized by large LCRs synchronized in space and time towards late diastole, dysrhythmic and dormant SANC exhibited smaller LCRs that appeared stochastically and were widely distributed in time. β-adrenergic receptor (βAR) stimulation increased LCR size and synchronized LCR occurrences in all dysrhythmic and a third of dormant cells (25 of 75 cells tested). In response to βAR stimulation, these dormant SANC developed automaticity, and LCRs became coupled to spontaneous action potential-induced cytosolic Ca 2+ transients. Conversely, dormant SANC that did not develop automaticity showed no significant change in average LCR characteristics. The majority of dysrhythmic cells became rhythmic in response to βAR stimulation, with the rate of action potential-induced cytosolic Ca 2+ transients substantially increasing. In summary, isolated SANC can be broadly categorized into three major populations: dormant, dysrhythmic, and rhythmic. We interpret our results based on simulations of a numerical model of SANC operating as a coupled-clock system. On this basis, the two previously unstudied dysrhythmic and dormant cell populations have intrinsically partially or completely uncoupled clocks. Such cells can be recruited to fire rhythmically in response to βAR stimulation via increased rhythmic LCR activity and ameliorated coupling between the Ca 2+ and membrane clocks.
AB - Current understanding of how cardiac pacemaker cells operate is based mainly on studies in isolated single sinoatrial node cells (SANC), specifically those that rhythmically fire action potentials similar to the in vivo behavior of the intact sinoatrial node. However, only a small fraction of SANC exhibit rhythmic firing after isolation. Other SANC behaviors have not been studied. Here, for the first time, we studied all single cells isolated from the sinoatrial node of the guinea pig, including traditionally studied rhythmically firing cells (‘rhythmic SANC’), dysrhythmically firing cells (‘dysrhythmic SANC’) and cells without any apparent spontaneous firing activity (‘dormant SANC’). Action potential-induced cytosolic Ca 2+ transients and spontaneous local Ca 2+ releases (LCRs) were measured with a 2D camera. LCRs were present not only in rhythmically firing SANC, but also in dormant and dysrhythmic SANC. While rhythmic SANC were characterized by large LCRs synchronized in space and time towards late diastole, dysrhythmic and dormant SANC exhibited smaller LCRs that appeared stochastically and were widely distributed in time. β-adrenergic receptor (βAR) stimulation increased LCR size and synchronized LCR occurrences in all dysrhythmic and a third of dormant cells (25 of 75 cells tested). In response to βAR stimulation, these dormant SANC developed automaticity, and LCRs became coupled to spontaneous action potential-induced cytosolic Ca 2+ transients. Conversely, dormant SANC that did not develop automaticity showed no significant change in average LCR characteristics. The majority of dysrhythmic cells became rhythmic in response to βAR stimulation, with the rate of action potential-induced cytosolic Ca 2+ transients substantially increasing. In summary, isolated SANC can be broadly categorized into three major populations: dormant, dysrhythmic, and rhythmic. We interpret our results based on simulations of a numerical model of SANC operating as a coupled-clock system. On this basis, the two previously unstudied dysrhythmic and dormant cell populations have intrinsically partially or completely uncoupled clocks. Such cells can be recruited to fire rhythmically in response to βAR stimulation via increased rhythmic LCR activity and ameliorated coupling between the Ca 2+ and membrane clocks.
KW - Local calcium release
KW - Pacemaker
KW - Ryanodine receptor
KW - Sarcoplasmic reticulum
KW - Sinoatrial node
KW - β Adrenergic receptor
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U2 - 10.1016/j.ceca.2018.07.002
DO - 10.1016/j.ceca.2018.07.002
M3 - Article
C2 - 30092494
AN - SCOPUS:85050980089
SN - 0143-4160
VL - 74
SP - 168
EP - 179
JO - Cell Calcium
JF - Cell Calcium
ER -