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The concentration of uncoupling protein correlates with Mg2+ activated mitochondrial binding of GDP
1Department of Nutritional Sciences, University of Wisconsin--Madison 53706.
Abstract:
Rats were housed at 4 degrees C for periods of up to 26 days. As little as 2 h of cold exposure caused an increase in the binding of [3H]GDP to mitochondria from brown adipose tissue. Incubation of mitochondria in vitro with 10 mM Mg2+ caused a marked increase in the subsequent binding of GDP to mitochondria from rats housed at 28 degrees C and a smaller increase in that from rats exposed to 4 degrees C for 2 h. Chronic exposure to cold led to an even greater increase in the amount of GDP bound to mitochondria incubated with Mg2+. The time course for the increase in the concentration of uncoupling protein was compared with that for GDP binding to mitochondria with and without Mg2+ treatment. The concentration of uncoupling protein appears to be correlated with the GDP-binding values for mitochondria treated with Mg2+ (r = 0.70) but not with the GDP binding to untreated mitochondria (r = 0.36). Therefore, the binding of GDP to untreated mitochondria may represent thermogenic activity at the time of death, whereas that after treatment with Mg2+ may more closely reflect total thermogenic capacity of the mitochondrion.
Insights
Cold exposure increases brown adipose tissue mitochondrial GDP binding in rats. Magnesium treatment reveals a stronger correlation with uncoupling protein, indicating total thermogenic capacity.
Area of Science:
- Biochemistry
- Physiology
- Thermogenesis
Background:
- Brown adipose tissue (BAT) is crucial for non-shivering thermogenesis.
- Mitochondrial GDP binding is a common indicator of BAT thermogenic capacity.
Purpose of the Study:
- To investigate the effect of cold exposure on mitochondrial GDP binding in rat BAT.
- To compare GDP binding with and without Mg2+ treatment in relation to uncoupling protein concentration.
Main Methods:
- Rats were housed at 4°C or 28°C for varying durations.
- Mitochondria were isolated from brown adipose tissue.
- GDP binding assays were performed with and without Mg2+ pre-incubation.
- Uncoupling protein concentration was measured.
Main Results:
- Cold exposure (even 2 hours) increased [3H]GDP binding to BAT mitochondria.
- Mg2+ pre-incubation significantly enhanced GDP binding, especially after chronic cold exposure.
- Uncoupling protein concentration correlated with Mg2+-treated GDP binding (r=0.70) but not untreated binding (r=0.36).
Conclusions:
- GDP binding to untreated mitochondria may reflect acute thermogenic activity.
- Mg2+-treated GDP binding appears to be a better indicator of the total thermogenic capacity of BAT mitochondria.
- Cold adaptation leads to increased mitochondrial thermogenic potential in brown adipose tissue.