Abstract
To investigate diversity of mitochondrial contents and metabolic features in various tissues, the respirationrates of mitochondria and activities of cytochrome c oxidase (CCO) in heart, kidney, liver, brain and white muscle ofsouthern catfish (Silurus meridionalis Chen) were measured at temperatures of 7.5, 10, 12.5, 17.5, 22.5, 27.5, 32.5, 35,and 37.5℃, respectively. At 27.5℃, state 3 rates were 69.94 in heart, 30.98 in kidney, 32.36 in liver, 18.89 in brain, and7.34 nmol O2 / min · mg in white muscle, respectively. And activities of CCO were 676.54 nmol O2 / min · mg in heart,compared with 327.46 in kidney, 294.34 in liver, 153.23 in brain, and 65.73 in white muscle. Statistical analysis indicatedthat either state 3 rates or activities of CCO showed the similar comparative trends among the five tissues. Eitherof the two values were significantly higher in heart than those in the other four tissues (P 0.05), and significantlylower in white muscle than those in the others (P 0.05). The two values in brain were significantly lower than those inkidney and liver, but there was no significant difference between kidney and liver. The global mitochondrial contentswere evaluated by the activity of citrate synthase (CS) in various tissues in the present study. At 27.5℃, the values were17.93 in heart, 7.20 in kidney, 8.42 in liver, 6.12 in brain, and 1.35 U / mg in white muscle, respectively. Heart presentedthe significantly highest value compared with the other four tissues, and white muscle presented the significantly lowestvalue (P 0.05). There was no significant difference for activities of CS among kidney, liver and brain. From 7.5 to32.5℃, either state 3 rates or activities of CCO increased respectively with increasing temperature in all of the five tissues.But both indexes in heart began to decline dramatically from 32.5℃ to 37.5℃. Values of the respiratory controlratio (RCR) almost were less than 4 at low (7.5℃—10℃) and high (35℃—37.5℃) temperature rang. RCR for whitemuscle at 7.5℃ and for heart at 37.5℃ presented very low values of 1.85 and 1.86, respectively. Based on the presentresults, it could be suggested that activity of CS could be used as an indirect index to compare mitochondrial contentamong various tissues in the southern catfish. And the mitochondrial content and metabolic capacity were significantlyvariable among different tissues. Heart presents with the higher mitochondrial content, higher metabolic capacity, andlower tolerable capacity against the extremely high temperatures. White muscle showed the lower mitochondrial content,lower metabolic capacity, and lower tolerable capacity against the extremely low temperature. Kidney, liver and braincharacterized by middle mitochondrial content, middle metabolic capacity of mitochondria and a higher tolerable capacityagainst the either extremely low or high temperatures.
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