Comparative Studies On Metabolism Of Mitochondria Isolated From Different Tissues Of Silurus Meridionalis,Carassius Auratus And Megalobrama Amblycephala In The Presence Of Various Substrates

In order to propose the suitable substrates for the experimental studies on the comparison of mitochondrial metabolic function among different fish species or different tissues and to evaluate the differences in mitochondrial respiratory function for different tissues or different species,respiration rates of mitochondria isolated from liver(Hepatopancreas),kidney,heart,brain and red muscle of S.meridionalis,C.auratus and M.amblycephala were measured in the presence of different substrates(complex I linked substrates: pyruvate + malate,glutamate +malate;complex II linked substrates:β-hydroxybutyrate,succinate;mixture of all substrates above),respectively.The preference of substrate utilization of mitochondria isolated from various tissues was investigated.And activities of cytochrome coxidase(CCO)in various tissues were also estimated.The main results were as follows:1.In the presence of the β-hydroxybutyrate,the respiratory control rate(RCR)of mitochondria in each tissue of S.meridionalis,C.auratus and M.amblycephala ranged from 1.19-2.61,i.e.,the β-hydroxybutyrate was not utilized effectively during mitochondrial oxidative phosphorylation.2.The coupling efficiency of mitochondria in each tissue of three fish species with complex Ⅰlinked substrates were higher than that with complex Ⅱ linked substrate.3.The RCR values of mitochondria of each fish species were all above 4 with all substrates except for β-hydroxybutyrate.And their coupling efficiencies were relatively higher compared with other tissues.4.The state 3 rates in each tissue mitochondria of three fish species varied with type of substrates,suggesting the obvious preference of substrate utilization.Furthermore,such substrate preference was also found in the same tissue mitochondria among different fish species.5.In general,state 3 rates of mitochondria with mixture as substrate were higher than that with single substrate.6.State 3 rates of mitochondria in heart with mixture as substrate were significantly higher than that in the kidney,liver(Hepatopancreas),brain and red muscle(P < 0.05).State 3rates of mitochondria in red muscle of C.auratus and M.amblycephala were significantly higher than that in brain,hepatopancreas and kidney(P < 0.05).But there was no significant difference for this index among brain,liver(Hepatopancreas)and kidney of each experimental fish.7.State 3 rates of mitochondria in heart of M.amblycephala were significantly higher than those from S.meridionalis and C.auratus,respectively(P < 0.05).The index of cardiac mitochondria of C.auratus was significantly higher in comparison with S.meridionalis(P< 0.05).There was no difference for state 3 rates of mitochondria in red muscle between the S.meridionalis and C.auratus.State 3 rates of mitochondria in kidney,liver(hepatopancreas)and brain varied greatly among three fish species.8.Except for hepatopancreas of M.amblycephala,state 4 rates of mitochondria for the same tissues with complex Ⅱ linked substrate were significantly higher than those with single substrate(P < 0.05).State 4 rates of mitochondria were relatively low with complex Ⅱlinked substrate in same tissue for all species.9.For all fish species,the activities of CCO in heart were the highest,followed by red muscle.The activities of CCO in brain,liver(hepatopancreas)and kidney were relatively low.There were significant differences in the CCO activity of cardiac mitochondria among different fish species.The order of the index was as follows: M.amblycephala>C.auratus>S.meridionalis.Statistical analysis showed that the differences of CCO activity among the three species were significant(P < 0.05).The main conclusions were as follows:1.The mitochondria isolated from heart,kidney,liver(Hepatopancreas),brain and red muscle of S.meridionalis,C.auratus and M.amblycephala all exhibited substrate preferences.Mitochondria in same tissue of different species also showed different preferences for substrate utilization.In the presence of complex Ⅰ linked substrates,mitochondria possessed higher coupling efficiency and lower leak rate,which were opposite to complex Ⅱ linked substrates.2.The maximum respiration rates of mitochondria in each tissue of S.meridionalis,C.auratus and M.amblycephala in the presence of substrate mixture were generally higher than that with single substrate.The oxygen consumption rate of state 3 measured under the condition of substrate mixture could reflect the maximum metabolic capacity of mitochondria.3.The differences of state 3 rates and activities of CCO in various tissues of S.meridionalis,C.auratus and M.amblycephala showed similarly trend: metabolic rates of mitochondria in heart were the highest,followed by red muscle,and the metabolic level of mitochondria in brain,kidney and liver(hepatopancreas)were relatively low.4.Feeding habits differences of species were not reflected in mitochondrial substrate preferences.5.The levels of maximum oxygen consumption of mitochondria isolated from heart in the presence of substrate mixture could reflect the difference in locomotor performance among different species.The fish with stronger capacity for sustained swimming should have higher metabolic rates of the mitochondria in the heart.