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Crosstalk between mitochondrial and sarcoplasmic reticulum Ca2+ cycling modulates cardiac pacemaker cell automaticity.

Yaniv Y, Spurgeon HA, Lyashkov AE, Yang D, Ziman BD, Maltsev VA, Lakatta EG - PLoS ONE (2012)

Bottom Line: Concurrent with inhibition of mitochondrial Ca(2+) influx or efflux, the SR Ca(2+) load, and LCR size, duration, amplitude and period (imaged via confocal linescan) significantly increased or decreased, respectively.Changes in total ensemble LCR Ca(2+) signal were highly correlated with the change in the SR Ca(2+) load (r(2) = 0.97).A change in SANC Ca(2+) (m) flux translates into a change in the AP firing rate by effecting changes in Ca(2+) (c) and SR Ca(2+) loading, which affects the characteristics of spontaneous SR Ca(2+) release.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America.

ABSTRACT

Background: Mitochondria dynamically buffer cytosolic Ca(2+) in cardiac ventricular cells and this affects the Ca(2+) load of the sarcoplasmic reticulum (SR). In sinoatrial-node cells (SANC) the SR generates periodic local, subsarcolemmal Ca(2+) releases (LCRs) that depend upon the SR load and are involved in SANC automaticity: LCRs activate an inward Na(+)-Ca(2+) exchange current to accelerate the diastolic depolarization, prompting the ensemble of surface membrane ion channels to generate the next action potential (AP).

Objective: To determine if mitochondrial Ca(2+) (Ca(2+) (m)), cytosolic Ca(2+) (Ca(2+) (c))-SR-Ca(2+) crosstalk occurs in single rabbit SANC, and how this may relate to SANC normal automaticity.

Results: Inhibition of mitochondrial Ca(2+) influx into (Ru360) or Ca(2+) efflux from (CGP-37157) decreased [Ca(2+)](m) to 80 ± 8% control or increased [Ca(2+)](m) to 119 ± 7% control, respectively. Concurrent with inhibition of mitochondrial Ca(2+) influx or efflux, the SR Ca(2+) load, and LCR size, duration, amplitude and period (imaged via confocal linescan) significantly increased or decreased, respectively. Changes in total ensemble LCR Ca(2+) signal were highly correlated with the change in the SR Ca(2+) load (r(2) = 0.97). Changes in the spontaneous AP cycle length (Ru360, 111 ± 1% control; CGP-37157, 89 ± 2% control) in response to changes in [Ca(2+)](m) were predicted by concurrent changes in LCR period (r(2) = 0.84).

Conclusion: A change in SANC Ca(2+) (m) flux translates into a change in the AP firing rate by effecting changes in Ca(2+) (c) and SR Ca(2+) loading, which affects the characteristics of spontaneous SR Ca(2+) release.

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SR load estimation from rapid caffeine application.Effects of a rapid application (“spritz”) of caffeine (indicated by the arrow) onto SANC (A) in control, or (B) in the presence of Ru360 or (C) CGP-37157. (D) Average effects of Ru360 or CGP-37157 on peak AP-induced cytosolic Ca2+ prior to a caffeine spritz (left), and the subsequent caffeine-induced cytosolic Ca2+ transient (right) (n = 12, for each group). (The caffeine response can be usually measured only once in a given SANC, because following caffeine application a prolonged period is required for AP firing rate to return to the control AP firing rate. Therefore, the effects of caffeine before (i.e. control) and following application of drugs that affect Ca2+m flux were measured in different cells).
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pone-0037582-g003: SR load estimation from rapid caffeine application.Effects of a rapid application (“spritz”) of caffeine (indicated by the arrow) onto SANC (A) in control, or (B) in the presence of Ru360 or (C) CGP-37157. (D) Average effects of Ru360 or CGP-37157 on peak AP-induced cytosolic Ca2+ prior to a caffeine spritz (left), and the subsequent caffeine-induced cytosolic Ca2+ transient (right) (n = 12, for each group). (The caffeine response can be usually measured only once in a given SANC, because following caffeine application a prolonged period is required for AP firing rate to return to the control AP firing rate. Therefore, the effects of caffeine before (i.e. control) and following application of drugs that affect Ca2+m flux were measured in different cells).

Mentions: Changes in AP triggered Ca2+ transient in response to perturbing Ca2+m flux (Fig. 2C) could change the SR Ca2+ loading. Specifically, inhibition of Ca2+m influx, while reducing [Ca2+]m (Fig. 2A), might result in more Ca2+ within the cytosol available for pumping into the SR; conversely, inhibition of Ca2+m efflux to increase [Ca2+]m might “steal” Ca2+ from the cytosol, resulting in reduced Ca2+ pumping into the SR. To estimate changes in the SR content, brief rapid applications of caffeine were applied (“spritzed”) onto the cell following drug application to perturb Ca2+m flux. Representative examples and average data are presented in Figures 3A–C and Fig. 3D (right bars), respectively. Blocking Ca2+ influx into mitochondria increased the SR Ca2+ load (assessed by change in amplitude of the Ca2+ transient induced by a brief rapid application of caffeine) by 17±5% of control (1.6±0.05 to 1.9±0.08 F/F0; p = 0.01); conversely inhibition of Ca2+ efflux from mitochondria reduced the SR Ca2+ load by 13±2% of control (1.6±0.05 to 1.4±0.03 F/F0; p = 0.03) (Fig. 3D, right bars). Although CGP-37157 reduced the rate of decay of the caffeine-evoked response compared to Ru360, this decrease was not significant. The change in the AP-induced Ca2+ transient amplitude by Ru360 or CGP-37157 prior to caffeine application (Fig. 3D, left bars) is similar to the trend measured by Indo-1 (Table 3). Note that the relative drug-induced changes in the caffeine and AP-induced cytosolic Ca2+ transient amplitudes and changes in Ca2+m and cycle length are all roughly equivalent. Thus, the changes in the amplitude of systolic Ca2+c transient due to manipulation of Ca2+m flux, could, in part at least, be due to changes in the SR Ca2+ load. Although, Ru360 and CGP-37157 tended to increase and decrease, respectively, the PLB phosphorylation at Serine-16 (PKA-dependent site), these effects were not statistically significant (Fig. S4). Note, however, that isoproterenol, employed as a positive control, markedly increases PLB phosphorylation.


Crosstalk between mitochondrial and sarcoplasmic reticulum Ca2+ cycling modulates cardiac pacemaker cell automaticity.

Yaniv Y, Spurgeon HA, Lyashkov AE, Yang D, Ziman BD, Maltsev VA, Lakatta EG - PLoS ONE (2012)

SR load estimation from rapid caffeine application.Effects of a rapid application (“spritz”) of caffeine (indicated by the arrow) onto SANC (A) in control, or (B) in the presence of Ru360 or (C) CGP-37157. (D) Average effects of Ru360 or CGP-37157 on peak AP-induced cytosolic Ca2+ prior to a caffeine spritz (left), and the subsequent caffeine-induced cytosolic Ca2+ transient (right) (n = 12, for each group). (The caffeine response can be usually measured only once in a given SANC, because following caffeine application a prolonged period is required for AP firing rate to return to the control AP firing rate. Therefore, the effects of caffeine before (i.e. control) and following application of drugs that affect Ca2+m flux were measured in different cells).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3362629&req=5

pone-0037582-g003: SR load estimation from rapid caffeine application.Effects of a rapid application (“spritz”) of caffeine (indicated by the arrow) onto SANC (A) in control, or (B) in the presence of Ru360 or (C) CGP-37157. (D) Average effects of Ru360 or CGP-37157 on peak AP-induced cytosolic Ca2+ prior to a caffeine spritz (left), and the subsequent caffeine-induced cytosolic Ca2+ transient (right) (n = 12, for each group). (The caffeine response can be usually measured only once in a given SANC, because following caffeine application a prolonged period is required for AP firing rate to return to the control AP firing rate. Therefore, the effects of caffeine before (i.e. control) and following application of drugs that affect Ca2+m flux were measured in different cells).
Mentions: Changes in AP triggered Ca2+ transient in response to perturbing Ca2+m flux (Fig. 2C) could change the SR Ca2+ loading. Specifically, inhibition of Ca2+m influx, while reducing [Ca2+]m (Fig. 2A), might result in more Ca2+ within the cytosol available for pumping into the SR; conversely, inhibition of Ca2+m efflux to increase [Ca2+]m might “steal” Ca2+ from the cytosol, resulting in reduced Ca2+ pumping into the SR. To estimate changes in the SR content, brief rapid applications of caffeine were applied (“spritzed”) onto the cell following drug application to perturb Ca2+m flux. Representative examples and average data are presented in Figures 3A–C and Fig. 3D (right bars), respectively. Blocking Ca2+ influx into mitochondria increased the SR Ca2+ load (assessed by change in amplitude of the Ca2+ transient induced by a brief rapid application of caffeine) by 17±5% of control (1.6±0.05 to 1.9±0.08 F/F0; p = 0.01); conversely inhibition of Ca2+ efflux from mitochondria reduced the SR Ca2+ load by 13±2% of control (1.6±0.05 to 1.4±0.03 F/F0; p = 0.03) (Fig. 3D, right bars). Although CGP-37157 reduced the rate of decay of the caffeine-evoked response compared to Ru360, this decrease was not significant. The change in the AP-induced Ca2+ transient amplitude by Ru360 or CGP-37157 prior to caffeine application (Fig. 3D, left bars) is similar to the trend measured by Indo-1 (Table 3). Note that the relative drug-induced changes in the caffeine and AP-induced cytosolic Ca2+ transient amplitudes and changes in Ca2+m and cycle length are all roughly equivalent. Thus, the changes in the amplitude of systolic Ca2+c transient due to manipulation of Ca2+m flux, could, in part at least, be due to changes in the SR Ca2+ load. Although, Ru360 and CGP-37157 tended to increase and decrease, respectively, the PLB phosphorylation at Serine-16 (PKA-dependent site), these effects were not statistically significant (Fig. S4). Note, however, that isoproterenol, employed as a positive control, markedly increases PLB phosphorylation.

Bottom Line: Concurrent with inhibition of mitochondrial Ca(2+) influx or efflux, the SR Ca(2+) load, and LCR size, duration, amplitude and period (imaged via confocal linescan) significantly increased or decreased, respectively.Changes in total ensemble LCR Ca(2+) signal were highly correlated with the change in the SR Ca(2+) load (r(2) = 0.97).A change in SANC Ca(2+) (m) flux translates into a change in the AP firing rate by effecting changes in Ca(2+) (c) and SR Ca(2+) loading, which affects the characteristics of spontaneous SR Ca(2+) release.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America.

ABSTRACT

Background: Mitochondria dynamically buffer cytosolic Ca(2+) in cardiac ventricular cells and this affects the Ca(2+) load of the sarcoplasmic reticulum (SR). In sinoatrial-node cells (SANC) the SR generates periodic local, subsarcolemmal Ca(2+) releases (LCRs) that depend upon the SR load and are involved in SANC automaticity: LCRs activate an inward Na(+)-Ca(2+) exchange current to accelerate the diastolic depolarization, prompting the ensemble of surface membrane ion channels to generate the next action potential (AP).

Objective: To determine if mitochondrial Ca(2+) (Ca(2+) (m)), cytosolic Ca(2+) (Ca(2+) (c))-SR-Ca(2+) crosstalk occurs in single rabbit SANC, and how this may relate to SANC normal automaticity.

Results: Inhibition of mitochondrial Ca(2+) influx into (Ru360) or Ca(2+) efflux from (CGP-37157) decreased [Ca(2+)](m) to 80 ± 8% control or increased [Ca(2+)](m) to 119 ± 7% control, respectively. Concurrent with inhibition of mitochondrial Ca(2+) influx or efflux, the SR Ca(2+) load, and LCR size, duration, amplitude and period (imaged via confocal linescan) significantly increased or decreased, respectively. Changes in total ensemble LCR Ca(2+) signal were highly correlated with the change in the SR Ca(2+) load (r(2) = 0.97). Changes in the spontaneous AP cycle length (Ru360, 111 ± 1% control; CGP-37157, 89 ± 2% control) in response to changes in [Ca(2+)](m) were predicted by concurrent changes in LCR period (r(2) = 0.84).

Conclusion: A change in SANC Ca(2+) (m) flux translates into a change in the AP firing rate by effecting changes in Ca(2+) (c) and SR Ca(2+) loading, which affects the characteristics of spontaneous SR Ca(2+) release.

Show MeSH
Related in: MedlinePlus