COMPARATIVE STUDIES ON METABOLISM OF MITOCHONDRIA ISOLATED FROM VARIOUS TISSUES OF SOUTHERN CATFISH,SILURUS MERIDIONALIS CHEN

YAN Yu-Lian and XIE Xiao-Jun(Key Laboratory of Freshwater Fish Reproduction and Development(Ministry of Education),School of Life Sciences,Southwest University,Chongqing 400715)

Respiration rates of mitochondria;Mitochondrial content;Cytochrome c oxidase(CCO);Citrate synthase(CS);Silurus meridionalis Chen

To investigate diversity of mitochondrial contents and metabolic features in various tissues,the respiration rates of mitochondria and activities of cytochrome c oxidase(CCO) in heart,kidney,liver,brain and white muscle of southern 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°C,respectively.At 27.5°C,state 3 rates were 69.94 in heart,30.98 in kidney,32.36 in liver,18.89 in brain,and 7.34 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 indi-cated that either state 3 rates or activities of CCO showed the similar comparative trends among the five tissues.Either of the two values were significantly higher in heart than those in the other four tissues(P<0.05),and significantly lower in white muscle than those in the others(P<0.05).The two values in brain were significantly lower than those in kidney and liver,but there was no significant difference between kidney and liver.The global mitochondrial contents were evaluated by the activity of citrate synthase(CS) in various tissues in the present study.At 27.5°C,the values were 17.93 in heart,7.20 in kidney,8.42 in liver,6.12 in brain,and 1.35 U/mg in white muscle,respectively.Heart presented the significantly highest value compared with the other four tissues,and white muscle presented the significantly lowest value(P<0.05).There was no significant difference for activities of CS among kidney,liver and brain.From 7.5 to 32.5℃,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 control ratio(RCR) almost were less than 4 at low(7.5℃—10℃) and high(35℃—37.5℃) temperature rang.RCR for white muscle at 7.5℃ and for heart at 37.5℃ presented very low values of 1.85 and 1.86,respectively.Based on the present results,it could be suggested that activity of CS could be used as an indirect index to compare mitochondrial content among various tissues in the southern catfish.And the mitochondrial content and metabolic capacity were significantly variable among different tissues.Heart presents with the higher mitochondrial content,higher metabolic capacity,and lower 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 brain characterized by middle mitochondrial content,middle metabolic capacity of mitochondria and a higher tolerable capacity against the either extremely low or high temperatures.