The influence of GDP on Ca2+ uptake by mitochondria of brown adipose tissue from lean and genetically obese (ob/ob) mice.
The specific binding capacity for purine nucleotides in brown-adipose-tissue mitochondria is thought to indicate the capacity of the proton-conductance pathway which leads to uncoupled respiration. This functional relationship was investigated in studies measuring initial Ca2+-uptake rates and membrane potential in the presence or absence of GDP in brown-adipose-tissue mitochondria with different GDP-binding capacities. The mitochondria from pre-obese and obese ob/ob mice were less able than those from lean control mice to dissipate membrane potential in the absence of GDP. Mitochondria from the obese animals also maintained a higher Ca2+-uptake rate without GDP in comparison with the rate found with mitochondria from the lean mice. The GDP-dependence of Ca2+ uptake was greater in brown-adipose-tissue mitochondria from cold-adapted animals than in those from animals kept at 22 degrees C or at thermoneutrality (33 degrees C). It is concluded that Ca2+-uptake rate and membrane-potential values are depressed in the absence of GDP and indicate indirectly the influence of purine nucleotides on maintaining the proton electrochemical gradient in brown-adipose-tissue mitochondria. It is also apparent that the lower GDP-binding capacity in mitochondria from ob/ob mice is related to a decreased ability to dissipate the proton electrochemical gradient.
D002001:Adipose Tissue, Brown / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D005260:Female; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008820:Mice, Obese; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009765:Obesity / Q000378:metabolism*; D013696:Temperature
D006150:Guanine Nucleotides; D006153:Guanosine Diphosphate; D002118:Calcium