Functional Difference Of Malate-aspartate Shuttle System In Liver Between Plateau Pika (Ochotona Curzoniae) And Plateau Zokor(Myospalax Rufescens Baileyi)

To explore the adaptive mechanisms of plateau pika to the sprint running activityand of plateau zokor to the enduring digging activity in the hypoxic environment atdifferent altitudes, the functional difference of malate-aspartate shuttle system (MA) inliver of plateau pika and plateau zokor were studied. The ratio of liver weight to bodyweight and the contents of lactic acid in serum were measured; the open reading frame ofcytoplasmic malate dehydrogenase (MDH1), mitochondrial malate dehydrogenase(MDH2) and the partial sequence of aspartate glutamate carrier (AGC) and oxoglutaratemalate carrier (OMC) genes were cloned and sequenced; MDH1, MDH2, AGC and OMCmRNA levels were determined by real-time PCR; the isoenzyme spectrum of MDH andthe activity of MDH1and MDH2in liver of plateau pika and plateau zokor determinedby using of enzymatic methods. The results showed that,(1) the ratio of liver weight tobody weight and the mRNA expression levels of MDH1and MDH2in liver of plateaupika at defferent altitudes had no defference (P>0.05); the activity of MDH2in liver ofpika at higher altitude was significant higher than that of lower altitude, but had nodifference of MDH1; at the same altitude, the mRNA expression levels and the activity ofMDH1decreased significantly than that of MDH2(P<0.01) in liver of plateau pika;(2)The ratio of liver weight to body weight and the mRNA expression levels of MDH1andMDH2in liver of plateau zokor at defferent altitudes had no defference (P>0.05); in liverof plateau zokor at lower altitude, the mRNA expression level of MDH2decreasedsignificantly than that of higher altitude (P<0.01), and the expression levels of MDH1had no difference between the two altitudes (P>0.05); at higher altitude, the activity ofMDH2was significant higher than MDH1, but that was not deffererent at lower altitude(P>0.05).(3)①The ratio of liver weight to body weight in liver of plateau zokor wasmarkedly higher than that of plateau pika (P<0.01), but the contents of lactic acid inserum of plateau pika was significantly higher than that of plateau zokor (P<0.01);②MDH1and MDH2mRNA levels as well as their enzymatic activity in liver of plateauzokor were significantly higher than that of plateau pika (P<0.01or P<0.05), AGCmRNA level of the zokor was significantly higher than that of the pika (P<0.01), whileno difference was found at OMC mRNA level between them (P>0.05);③mRNA level and enzymatic activitiy of MDH1was significantly lower than that of MDH2in liver ofpika (P<0.01), MDH1mRNA level of plateau zokor was markedly higher than that ofMDH2(P<0.01), but the activity had no difference between MDH1and MDH2in liverof zokor (P>0.05). Theses results indicates that the plateau pika gets glycogen for theirsprint running activity by increasing the process of gluconeogenesis, converts the lacticacid quickly produced in their skeletal muscle by anaerobic glycolysis, while plateauzokor obtains ATP in the enduring digging activity by enhancing the function of MA.