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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 different mouse tissuesWhole-mitoplast current recorded before (black traces) and after (red traces) application of 100 μM Ca2+ to the bath solution. Currents were elicited by a voltage-ramp protocol (shown above) from different mouse tissues (as indicated). Note that brown fat mitoplasts were isolated from mice deficient for uncoupling protein 1 (UCP1, see methods). Whole-mitoplast IMCU was normalized to the membrane capacitance (Cm) in all tissues examined. Picture in inset, representative transmitted DIC image of a mouse heart mitoplast obtained with French press. Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM was less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow). Bottom right panel: Histogram showing average IMCU current densities in 100 μM Ca2+ in different tissues. Current amplitudes were measured at 5 ms after stepping from 0 mV to −160 mV (see the voltage protocol). Note the low IMCU current density in heart compared to other tissues. Statistical data are represented as mean ± SEM.
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Figure 1: Mitochondrial Ca2+ conductance in different mouse tissuesWhole-mitoplast current recorded before (black traces) and after (red traces) application of 100 μM Ca2+ to the bath solution. Currents were elicited by a voltage-ramp protocol (shown above) from different mouse tissues (as indicated). Note that brown fat mitoplasts were isolated from mice deficient for uncoupling protein 1 (UCP1, see methods). Whole-mitoplast IMCU was normalized to the membrane capacitance (Cm) in all tissues examined. Picture in inset, representative transmitted DIC image of a mouse heart mitoplast obtained with French press. Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM was less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow). Bottom right panel: Histogram showing average IMCU current densities in 100 μM Ca2+ in different tissues. Current amplitudes were measured at 5 ms after stepping from 0 mV to −160 mV (see the voltage protocol). Note the low IMCU current density in heart compared to other tissues. Statistical data are represented as mean ± SEM.

Mentions: Figure 1 (see picture in the inset) shows a differential interference contrast (DIC) image of a mouse heart mitoplast obtained with the French press method. In 150 mM KCl solution, mitoplasts generated with the French press method normally have a figure 8-shaped form, as the IMM protrudes through one of small ruptures in the OMM to produce a bilobed vesicle. The lobe of the mitoplast covered with remnants of the OMM (inset, red arrow) appeared optically denser (as it contained two membranes) than the lobe consisting of the IMM only (inset, white arrow). After strorage on ice for several hours, mitoplasts assumed a round shape with the remnants of the OMM attached from one side (the so-called “cap” region). We found that the newly prepared figure 8-shaped mitoplasts were the best choice for the formation of the whole-mitoplast mode, while the success rate in the formation of this mode with older round-shaped mitoplasts was lower.


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 different mouse tissuesWhole-mitoplast current recorded before (black traces) and after (red traces) application of 100 μM Ca2+ to the bath solution. Currents were elicited by a voltage-ramp protocol (shown above) from different mouse tissues (as indicated). Note that brown fat mitoplasts were isolated from mice deficient for uncoupling protein 1 (UCP1, see methods). Whole-mitoplast IMCU was normalized to the membrane capacitance (Cm) in all tissues examined. Picture in inset, representative transmitted DIC image of a mouse heart mitoplast obtained with French press. Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM was less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow). Bottom right panel: Histogram showing average IMCU current densities in 100 μM Ca2+ in different tissues. Current amplitudes were measured at 5 ms after stepping from 0 mV to −160 mV (see the voltage protocol). Note the low IMCU current density in heart compared to other tissues. Statistical data are represented as mean ± SEM.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3818247&req=5

Figure 1: Mitochondrial Ca2+ conductance in different mouse tissuesWhole-mitoplast current recorded before (black traces) and after (red traces) application of 100 μM Ca2+ to the bath solution. Currents were elicited by a voltage-ramp protocol (shown above) from different mouse tissues (as indicated). Note that brown fat mitoplasts were isolated from mice deficient for uncoupling protein 1 (UCP1, see methods). Whole-mitoplast IMCU was normalized to the membrane capacitance (Cm) in all tissues examined. Picture in inset, representative transmitted DIC image of a mouse heart mitoplast obtained with French press. Note the figure 8-shaped form of the mitoplast. The lobe of the mitoplast containing only the IMM was less dense (white arrow) and clearly distinguishable from the lobe covered with the OMM (red arrow). Bottom right panel: Histogram showing average IMCU current densities in 100 μM Ca2+ in different tissues. Current amplitudes were measured at 5 ms after stepping from 0 mV to −160 mV (see the voltage protocol). Note the low IMCU current density in heart compared to other tissues. Statistical data are represented as mean ± SEM.
Mentions: Figure 1 (see picture in the inset) shows a differential interference contrast (DIC) image of a mouse heart mitoplast obtained with the French press method. In 150 mM KCl solution, mitoplasts generated with the French press method normally have a figure 8-shaped form, as the IMM protrudes through one of small ruptures in the OMM to produce a bilobed vesicle. The lobe of the mitoplast covered with remnants of the OMM (inset, red arrow) appeared optically denser (as it contained two membranes) than the lobe consisting of the IMM only (inset, white arrow). After strorage on ice for several hours, mitoplasts assumed a round shape with the remnants of the OMM attached from one side (the so-called “cap” region). We found that the newly prepared figure 8-shaped mitoplasts were the best choice for the formation of the whole-mitoplast mode, while the success rate in the formation of this mode with older round-shaped mitoplasts was lower.

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