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Activity of the mitochondrial calcium uniporter varies greatly between tissues.

Fieni F, Lee SB, Jan YN, Kirichok Y - Nat Commun (2012)

Bottom Line: Similarly, in Drosophila flight muscle, mitochondrial calcium uniporter activity is barely detectable compared with that in other fly tissues.As mitochondria occupy up to 40% of the cell volume in highly metabolically active heart and flight muscle, low mitochondrial calcium uniporter activity is likely essential to avoid cytosolic Ca(2+) sink due to excessive mitochondrial Ca(2+) uptake.Simultaneously, low mitochondrial calcium uniporter activity may also prevent mitochondrial Ca(2+) overload in such active tissues exposed to frequent cytosolic Ca(2+) activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, California 94158, USA.

ABSTRACT
The mitochondrial calcium uniporter is a highly selective channel responsible for mitochondrial Ca(2+) uptake. The mitochondrial calcium uniporter shapes cytosolic Ca(2+) signals, controls mitochondrial ATP production, and is involved in cell death. Here using direct patch-clamp recording from the inner mitochondrial membrane, we compare mitochondrial calcium uniporter activity in mouse heart, skeletal muscle, liver, kidney and brown fat. Surprisingly, heart mitochondria show a dramatically lower mitochondrial calcium uniporter current density than the other tissues studied. Similarly, in Drosophila flight muscle, mitochondrial calcium uniporter activity is barely detectable compared with that in other fly tissues. As mitochondria occupy up to 40% of the cell volume in highly metabolically active heart and flight muscle, low mitochondrial calcium uniporter activity is likely essential to avoid cytosolic Ca(2+) sink due to excessive mitochondrial Ca(2+) uptake. Simultaneously, low mitochondrial calcium uniporter activity may also prevent mitochondrial Ca(2+) overload in such active tissues exposed to frequent cytosolic Ca(2+) activity.

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Mitochondrial Ca2+ conductance in Drosophila flight muscle(a) Representative transmitted (left) and fluorescent (right) image of a French press-derived mitoplast isolated from flies expressing GFP targeted to the mitochondrial matrix of the flight muscle (Mef2>MitoGFP). Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM is less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow; compare to Fig. 1 inset). (b) Left panel: Representative mitochondrial Ca2+ current recorded from a Drosophila flight muscle mitoplast in different concentrations of bath Ca2+: 5 mM (green), 1 mM (red), and 100 μM (blue), and 5 mM Ca2+ plus 200 nM RuR (black). Voltage-ramp protocol is indicated on top. Right panel: Representative mitochondrial Ca2+ current recorded from a Drosophila not flight muscle mitoplast in the presence of different concentrations of Ca2+ in the bath: 1 mM (red) and 100 μM (blue), and 1 mM Ca2+ plus 200 nM RuR (black). (c) Left panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 100 μM in flight muscle (n= 8) and not flight muscle tissues (n=3). Right panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 1 mM in flight muscle (n= 21) and not flight muscle tissues (n=6). Current amplitudes were measured at 5 ms after stepping the membrane from 0 to −160 mV (see the voltage protocol). Statistical data are represented as mean ± SEM.
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Figure 6: Mitochondrial Ca2+ conductance in Drosophila flight muscle(a) Representative transmitted (left) and fluorescent (right) image of a French press-derived mitoplast isolated from flies expressing GFP targeted to the mitochondrial matrix of the flight muscle (Mef2>MitoGFP). Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM is less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow; compare to Fig. 1 inset). (b) Left panel: Representative mitochondrial Ca2+ current recorded from a Drosophila flight muscle mitoplast in different concentrations of bath Ca2+: 5 mM (green), 1 mM (red), and 100 μM (blue), and 5 mM Ca2+ plus 200 nM RuR (black). Voltage-ramp protocol is indicated on top. Right panel: Representative mitochondrial Ca2+ current recorded from a Drosophila not flight muscle mitoplast in the presence of different concentrations of Ca2+ in the bath: 1 mM (red) and 100 μM (blue), and 1 mM Ca2+ plus 200 nM RuR (black). (c) Left panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 100 μM in flight muscle (n= 8) and not flight muscle tissues (n=3). Right panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 1 mM in flight muscle (n= 21) and not flight muscle tissues (n=6). Current amplitudes were measured at 5 ms after stepping the membrane from 0 to −160 mV (see the voltage protocol). Statistical data are represented as mean ± SEM.

Mentions: We first studied Ca2+ currents in mitoplasts isolated from Drosophila flight muscle, which is of particular interest because this organ contracts at high frequencies. We obtained mitoplasts from thoraces of a Drosophila line in which the targeted mitochondrial expression of green fluorescent protein (GFP) in muscles was driven by crossing a UAS-MitoGFP line with a muscle specific Mef2-Gal4 line (see Methods for details). Flight muscle mitochondria from this line express GFP in the matrix; hence, mitoplasts originating from it fluoresce. Drosophila thoraces were cleaned of legs to reduce contamination from leg muscle mitochondria. Figure 6a shows a typical flight muscle GFP-fluorescent mitoplast used for patch-clamp recordings. Similar to mouse mitoplasts, Drosophila mitoplasts were obtained using the French press procedure and normally showed the same figure 8-shaped morphology (compare Fig. 6a and Fig. 1inset). The lobe that contained only the IMM was distinguishable from the optically denser lobe that was covered with the OMM and contained two membranes (Fig. 6a, white and red arrows, respectively).


Activity of the mitochondrial calcium uniporter varies greatly between tissues.

Fieni F, Lee SB, Jan YN, Kirichok Y - Nat Commun (2012)

Mitochondrial Ca2+ conductance in Drosophila flight muscle(a) Representative transmitted (left) and fluorescent (right) image of a French press-derived mitoplast isolated from flies expressing GFP targeted to the mitochondrial matrix of the flight muscle (Mef2>MitoGFP). Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM is less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow; compare to Fig. 1 inset). (b) Left panel: Representative mitochondrial Ca2+ current recorded from a Drosophila flight muscle mitoplast in different concentrations of bath Ca2+: 5 mM (green), 1 mM (red), and 100 μM (blue), and 5 mM Ca2+ plus 200 nM RuR (black). Voltage-ramp protocol is indicated on top. Right panel: Representative mitochondrial Ca2+ current recorded from a Drosophila not flight muscle mitoplast in the presence of different concentrations of Ca2+ in the bath: 1 mM (red) and 100 μM (blue), and 1 mM Ca2+ plus 200 nM RuR (black). (c) Left panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 100 μM in flight muscle (n= 8) and not flight muscle tissues (n=3). Right panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 1 mM in flight muscle (n= 21) and not flight muscle tissues (n=6). Current amplitudes were measured at 5 ms after stepping the membrane from 0 to −160 mV (see the voltage protocol). Statistical data are represented as mean ± SEM.
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Figure 6: Mitochondrial Ca2+ conductance in Drosophila flight muscle(a) Representative transmitted (left) and fluorescent (right) image of a French press-derived mitoplast isolated from flies expressing GFP targeted to the mitochondrial matrix of the flight muscle (Mef2>MitoGFP). Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM is less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow; compare to Fig. 1 inset). (b) Left panel: Representative mitochondrial Ca2+ current recorded from a Drosophila flight muscle mitoplast in different concentrations of bath Ca2+: 5 mM (green), 1 mM (red), and 100 μM (blue), and 5 mM Ca2+ plus 200 nM RuR (black). Voltage-ramp protocol is indicated on top. Right panel: Representative mitochondrial Ca2+ current recorded from a Drosophila not flight muscle mitoplast in the presence of different concentrations of Ca2+ in the bath: 1 mM (red) and 100 μM (blue), and 1 mM Ca2+ plus 200 nM RuR (black). (c) Left panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 100 μM in flight muscle (n= 8) and not flight muscle tissues (n=3). Right panel: Histogram comparing average densities of Drosophila mitochondrial Ca2+ current at 1 mM in flight muscle (n= 21) and not flight muscle tissues (n=6). Current amplitudes were measured at 5 ms after stepping the membrane from 0 to −160 mV (see the voltage protocol). Statistical data are represented as mean ± SEM.
Mentions: We first studied Ca2+ currents in mitoplasts isolated from Drosophila flight muscle, which is of particular interest because this organ contracts at high frequencies. We obtained mitoplasts from thoraces of a Drosophila line in which the targeted mitochondrial expression of green fluorescent protein (GFP) in muscles was driven by crossing a UAS-MitoGFP line with a muscle specific Mef2-Gal4 line (see Methods for details). Flight muscle mitochondria from this line express GFP in the matrix; hence, mitoplasts originating from it fluoresce. Drosophila thoraces were cleaned of legs to reduce contamination from leg muscle mitochondria. Figure 6a shows a typical flight muscle GFP-fluorescent mitoplast used for patch-clamp recordings. Similar to mouse mitoplasts, Drosophila mitoplasts were obtained using the French press procedure and normally showed the same figure 8-shaped morphology (compare Fig. 6a and Fig. 1inset). The lobe that contained only the IMM was distinguishable from the optically denser lobe that was covered with the OMM and contained two membranes (Fig. 6a, white and red arrows, respectively).

Bottom Line: Similarly, in Drosophila flight muscle, mitochondrial calcium uniporter activity is barely detectable compared with that in other fly tissues.As mitochondria occupy up to 40% of the cell volume in highly metabolically active heart and flight muscle, low mitochondrial calcium uniporter activity is likely essential to avoid cytosolic Ca(2+) sink due to excessive mitochondrial Ca(2+) uptake.Simultaneously, low mitochondrial calcium uniporter activity may also prevent mitochondrial Ca(2+) overload in such active tissues exposed to frequent cytosolic Ca(2+) activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, California 94158, USA.

ABSTRACT
The mitochondrial calcium uniporter is a highly selective channel responsible for mitochondrial Ca(2+) uptake. The mitochondrial calcium uniporter shapes cytosolic Ca(2+) signals, controls mitochondrial ATP production, and is involved in cell death. Here using direct patch-clamp recording from the inner mitochondrial membrane, we compare mitochondrial calcium uniporter activity in mouse heart, skeletal muscle, liver, kidney and brown fat. Surprisingly, heart mitochondria show a dramatically lower mitochondrial calcium uniporter current density than the other tissues studied. Similarly, in Drosophila flight muscle, mitochondrial calcium uniporter activity is barely detectable compared with that in other fly tissues. As mitochondria occupy up to 40% of the cell volume in highly metabolically active heart and flight muscle, low mitochondrial calcium uniporter activity is likely essential to avoid cytosolic Ca(2+) sink due to excessive mitochondrial Ca(2+) uptake. Simultaneously, low mitochondrial calcium uniporter activity may also prevent mitochondrial Ca(2+) overload in such active tissues exposed to frequent cytosolic Ca(2+) activity.

Show MeSH
Related in: MedlinePlus