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Control of mitochondrial motility and distribution by the calcium signal: a homeostatic circuit.

Yi M, Weaver D, Hajnóczky G - J. Cell Biol. (2004)

Bottom Line: By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range.The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility.This decrease followed the spatial and temporal pattern of the [Ca2+]c signal.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.

ABSTRACT
Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules. By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range. Maximal movement was obtained at resting [Ca2+]c with complete arrest at 1-2 microM. Movement was fully recovered by returning to resting [Ca2+]c, and inhibition could be repeated with no apparent desensitization. The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility. This decrease followed the spatial and temporal pattern of the [Ca2+]c signal. Diminished mitochondrial motility in the region of the [Ca2+]c rise promotes recruitment of mitochondria to enhance local Ca2+ buffering and energy supply. This mechanism may provide a novel homeostatic circuit in calcium signaling.

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Relationship between [Ca2+]c and mitochondrial motility. (A) Stepwise increases in [Ca2+]c induce stepped decreases in mitochondrial motility. MitoYFP-expressing and fura2-loaded cells were incubated in Ca2+-free ECM supplemented with 2 mM EGTA, 2 μM Tg, and 10 μM of Iono for 12 min. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells exposed to stepped increases in extracellular CaCl2 from 0 to 15 mM. [Ca2+]c was calibrated in terms of nanomoles using in vitro calibration of fura2. (B) Dose–response relationship between [Ca2+]c and mitochondrial motility. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells as described for A. Mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each [CaCl2]. Mean ± SEM are marked by filled circles (n = 68 cells from 40 experiments). The IC50 ≈ 400 nM, indicating that mitochondrial motility is controlled in the physiological range of [Ca2+]c. (C) Mitochondrial motility (red line) and [Ca2+]c (black line) were recorded in single cells stimulated by varying doses of VP (0.1–100 nM). In addition, the mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each VP concentration and are plotted in B (empty circles and dashed line; n = 44 cells from 28 experiments).
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fig2: Relationship between [Ca2+]c and mitochondrial motility. (A) Stepwise increases in [Ca2+]c induce stepped decreases in mitochondrial motility. MitoYFP-expressing and fura2-loaded cells were incubated in Ca2+-free ECM supplemented with 2 mM EGTA, 2 μM Tg, and 10 μM of Iono for 12 min. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells exposed to stepped increases in extracellular CaCl2 from 0 to 15 mM. [Ca2+]c was calibrated in terms of nanomoles using in vitro calibration of fura2. (B) Dose–response relationship between [Ca2+]c and mitochondrial motility. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells as described for A. Mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each [CaCl2]. Mean ± SEM are marked by filled circles (n = 68 cells from 40 experiments). The IC50 ≈ 400 nM, indicating that mitochondrial motility is controlled in the physiological range of [Ca2+]c. (C) Mitochondrial motility (red line) and [Ca2+]c (black line) were recorded in single cells stimulated by varying doses of VP (0.1–100 nM). In addition, the mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each VP concentration and are plotted in B (empty circles and dashed line; n = 44 cells from 28 experiments).

Mentions: When EGTA and Iono were added together to nonstimulated cells to lower the [Ca2+]c no change in mitochondrial movement activity was observed (n = 4; unpublished data), suggesting that the motility was maximal at the resting level of [Ca2+]c (50–100 nM). To quantitate the [Ca2+]c dependence of the inhibition of mitochondrial motility, [Ca2+]c and motility were measured in cells that were incubated in a Ca2+ free buffer supplemented with EGTA, thapsigargin (Tg), an inhibitor of the sarco-endoplasmic reticulum Ca2+ pump and Iono to ensure rapid equilibration of the cytosol with the extracellular [Ca2+], and then varying amounts of CaCl2 were added (Fig. 2, A and B). As shown in Fig. 2 A, stepwise increases in [Ca2+]c were accompanied with stepwise decreases in mitochondrial motility. The inhibition of motility was plotted against the [Ca2+]c (Fig. 2 B, filled circles). The majority of the Ca2+-induced attenuation of mitochondrial motility was obtained in the sub-micromolar range of [Ca2+]c (IC50 ≈ 400 nM), indicating that mitochondrial motility is controlled in the physiological range of [Ca2+]c.


Control of mitochondrial motility and distribution by the calcium signal: a homeostatic circuit.

Yi M, Weaver D, Hajnóczky G - J. Cell Biol. (2004)

Relationship between [Ca2+]c and mitochondrial motility. (A) Stepwise increases in [Ca2+]c induce stepped decreases in mitochondrial motility. MitoYFP-expressing and fura2-loaded cells were incubated in Ca2+-free ECM supplemented with 2 mM EGTA, 2 μM Tg, and 10 μM of Iono for 12 min. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells exposed to stepped increases in extracellular CaCl2 from 0 to 15 mM. [Ca2+]c was calibrated in terms of nanomoles using in vitro calibration of fura2. (B) Dose–response relationship between [Ca2+]c and mitochondrial motility. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells as described for A. Mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each [CaCl2]. Mean ± SEM are marked by filled circles (n = 68 cells from 40 experiments). The IC50 ≈ 400 nM, indicating that mitochondrial motility is controlled in the physiological range of [Ca2+]c. (C) Mitochondrial motility (red line) and [Ca2+]c (black line) were recorded in single cells stimulated by varying doses of VP (0.1–100 nM). In addition, the mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each VP concentration and are plotted in B (empty circles and dashed line; n = 44 cells from 28 experiments).
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Related In: Results  -  Collection

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fig2: Relationship between [Ca2+]c and mitochondrial motility. (A) Stepwise increases in [Ca2+]c induce stepped decreases in mitochondrial motility. MitoYFP-expressing and fura2-loaded cells were incubated in Ca2+-free ECM supplemented with 2 mM EGTA, 2 μM Tg, and 10 μM of Iono for 12 min. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells exposed to stepped increases in extracellular CaCl2 from 0 to 15 mM. [Ca2+]c was calibrated in terms of nanomoles using in vitro calibration of fura2. (B) Dose–response relationship between [Ca2+]c and mitochondrial motility. Simultaneous measurements of [Ca2+]c and mitochondrial motility were performed in single cells as described for A. Mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each [CaCl2]. Mean ± SEM are marked by filled circles (n = 68 cells from 40 experiments). The IC50 ≈ 400 nM, indicating that mitochondrial motility is controlled in the physiological range of [Ca2+]c. (C) Mitochondrial motility (red line) and [Ca2+]c (black line) were recorded in single cells stimulated by varying doses of VP (0.1–100 nM). In addition, the mean mitochondrial motility inhibition and mean [Ca2+]c were calculated for each VP concentration and are plotted in B (empty circles and dashed line; n = 44 cells from 28 experiments).
Mentions: When EGTA and Iono were added together to nonstimulated cells to lower the [Ca2+]c no change in mitochondrial movement activity was observed (n = 4; unpublished data), suggesting that the motility was maximal at the resting level of [Ca2+]c (50–100 nM). To quantitate the [Ca2+]c dependence of the inhibition of mitochondrial motility, [Ca2+]c and motility were measured in cells that were incubated in a Ca2+ free buffer supplemented with EGTA, thapsigargin (Tg), an inhibitor of the sarco-endoplasmic reticulum Ca2+ pump and Iono to ensure rapid equilibration of the cytosol with the extracellular [Ca2+], and then varying amounts of CaCl2 were added (Fig. 2, A and B). As shown in Fig. 2 A, stepwise increases in [Ca2+]c were accompanied with stepwise decreases in mitochondrial motility. The inhibition of motility was plotted against the [Ca2+]c (Fig. 2 B, filled circles). The majority of the Ca2+-induced attenuation of mitochondrial motility was obtained in the sub-micromolar range of [Ca2+]c (IC50 ≈ 400 nM), indicating that mitochondrial motility is controlled in the physiological range of [Ca2+]c.

Bottom Line: By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range.The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility.This decrease followed the spatial and temporal pattern of the [Ca2+]c signal.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.

ABSTRACT
Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules. By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range. Maximal movement was obtained at resting [Ca2+]c with complete arrest at 1-2 microM. Movement was fully recovered by returning to resting [Ca2+]c, and inhibition could be repeated with no apparent desensitization. The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility. This decrease followed the spatial and temporal pattern of the [Ca2+]c signal. Diminished mitochondrial motility in the region of the [Ca2+]c rise promotes recruitment of mitochondria to enhance local Ca2+ buffering and energy supply. This mechanism may provide a novel homeostatic circuit in calcium signaling.

Show MeSH
Related in: MedlinePlus