Effects Of Carbon Dioxide On The Respiratory And Circulation Activities Of Myospalax Baileyi

The plateau zokor?Myospalax baileyi?is one of the endemic species of Qinghai-Tibetan Plateau belonging to the genus Myospalax of the family of Spalacidae,and mainly lives in the eastern areas of the Qinghai-Tibet Plateau at altitude from 2000 to 4000 meters.The plateau zokor inhabits in the sealed burrow most of the time in its life,which is characterized by hypoxia?the content of oxygen is 20%lower than the atmosphere in the same area?and hypercania?the concentration of CO₂ is 30 times higher than that in the atmosphere in the same region,even up to48 times?.Moreover,the content of oxygen and carbon dioxide in burrows showed seasonal differences,but the plateau zokor showed excellent adaptability to the extreme condition.In the present study,we compared the respiratory frequency,blood pressure,heart rate and ventilation under air,hypercapnia and normoxic?5%CO₂+O₂ and 10%CO₂+O₂?,and hypercapnia?5%CO₂and 10%CO₂?inhalation between plateau zokors and rats.And blood-gas was measured in air and hypercapnia.Our results showed that plateau zokors had higher PCO₂,HCO₃^-,tCO₂ than rats.However,the p H,respiratory frequency,blood pressure and heart rate of plateau zokors were obviously lower than those of rats.The PO₂ of zokors increased faster than rats with elevation of inspired CO₂.The increment of ventilation of rats increased with the enhancement of carbon dioxide levels in inhalation gas.On the contrary,the increment of ventilation in zokors was reduced.In conclusion,the responses to acute hypercapnic in the plateau zokors were attenuated,and they had a strong tolerance to hypercapnic.Carbonic anhydrase as a versatile enzyme participates in many physiological process,especially accelerating the emission of carbon dioxide in the lungs and regulating the pH.In this experiment,we compared the amino acid sequence and the secondary structure of carbonic anhydrase of erythrocyte in plateau zokors and rats.Additionally,the three-dimensional structure of carbonic anhydrase was predicted by homology modeling.The results showed that the pocket of carbonic anhydrase in plateau zokor was significantly bigger than that in rat.The structural change may increase the affinity of the enzyme to carbon dioxide.Thereby,the change accelerated the hydration reaction of carbon dioxide,and enhanced adaptation to low oxygen and high carbon dioxide environment in the plateau zokor.