Difference in oxygen uptake in skeletal muscles between plateau zokor (Myospalax rufescens baileyi) and plateau pika (Ochotona curzoniac) / 生理学报

To investigate the difference between the functions of oxygen uptake in skeletal muscle and living habits of plateau zokor (Myospalax rufescens baileyi) and plateau pika (Ochotona curzoniac), the microvessel densities (MVD) of skeletal muscle of plateau zokor, plateau pika and Sprague-Dawley (SD) rat were measured by immunohistochemical staining; the numerical density on area (N(A)) of mitochondria, and surface density (S(V), external surface area density of mitochondria per unit volume of skeletal muscle fiber) were obtained by stereo microscope technique; mRNA levels of myoglobin (Mb) in skeletal muscle were determined by real-time PCR, and the contents of Mb protein in skeletal muscle were determined by spectro-photometer. The results showed that MVD, N(A) and S(V) of mitochondria in skeletal muscle of plateau pika were significantly lower than those of plateau zokor and SD rat (P<0.05). The mRNA levels of Mb gene in skeletal muscle of plateau zokor and plateau pika were notably higher than that of SD rat (P<0.05). There were significant differences in the contents of Mb among these three species, and plateau zokor and SD rat presented the highest and the lowest value, respectively (P<0.05). The results suggest that even though plateau zokor inhabits in the hypoxia environment, most of its skeletal muscle fiber are red muscle fiber. While most of skeletal muscle fibers of plateau pika are white muscle fibers. This kind of white muscle has low MVD, N(A) and S(V) of mitochondria and less content of Mb compared with the red one, suggesting it obtains most energy from aerobic oxidation. The above-mentioned differences in skeletal muscles may be related to not only the different species, but also the different living habits of these two high altitude species.

Hypoxic adaptation of the hearts of plateau zokor (Myospalax baileyi) and plateau pika (Ochotona curzoniae) / 生理学报

Plateau zokor (Myospalax baileyi) and plateau pika (Ochotona curzniae) are native to the Qinghai-Tibet plateau. To study their adaptive mechanisms, the ratios of heart weight to body weight (HW/BW) and right to left ventricular plus septum weights [RV/(LV+S)] were determined; the microvessel density (MVD) of cardiac muscle were measured by immunohistochemical staining; the numerical density on area (N(A)), volume density (V(V)), specific surface (δ), and surface density (S(V)) of mitochondria were obtained by microscopy and stereology; the contents of myoglobin (Mb) and lactic acid (LD), and the activity of lactate dehydrogenase (LDH) in cardiac muscle were analyzed by spectrophotometer. The results showed that the HW/BW of plateau zokor [(4.55±0.26)%] and plateau pika [(4.41±0.38)%] was significantly greater than that of Sprague-Dawley (SD) rat [(3.44±0.41)%] (P<0.05), but the RV/(LV+S) [(22.04±1.98)%, (25.53±3.41)%] was smaller than that of SD rats [(44.23±3.87)%] (P<0.05). The MVD and N(A) of cardiac muscle were 1688.631±250.253 and 0.768±0.123 in SD rat, 2002.888±367.466 and 0.868±0.159 in plateau pika and 2 990.643±389.888 and 1.012±0.133 in plateau zokor. The V(V) of mitochondria in plateau zokor (0.272±0.045) was significantly lower than that in plateau pika (0.343±0.039) and SD rat (0.321±0.048) (P<0.05), while the δ of mitochondria in plateau zokor (9.409±1.238) was higher than that in plateau pika (6.772±0.892) and SD rat (7.287±1.373) (P<0.05). The S(V) of mitochondria in plateau pika (2.322±0.347) was not obviously different from that in plateau zokor (2.468±0.380) and SD rat (2.227±0.377), but that in plateau zokor was significantly higher than that in SD rat (P<0.05). The contents of Mb in cardiac muscle of plateau zokor [(763.33±88.73) nmol/g] and plateau pika [(765.96±28.47) nmol/g] were significantly higher than that of SD rat [(492.38±72.14) nmol/g] (P<0.05), the content of LD in plateau zokor [(0.57±0.06) mmol/L] was obviously higher than that in plateau pika [(0.45±0.06) mmol/L] and SD rat [(0.48±0.02) mmol/L] (P<0.05), and the activity of LDH in plateau zokor [(16.90±2.00) U/mL] and plateau pika [(20.55±2.46) U/mL] were significantly lower than that in SD rat [(38.26±6.78) U/mL] (P<0.05). The percentage of LDH-H in cardiac muscle decreased in order in plateau zokor, plateau pika and SD rat. In conclusion, plateau zokor and plateau pika adapt better to hypoxia than SD rat by increasing the SV of mitochondria, MVD and content of Mb in the cardiac muscle. However, the parameters of mitochondria in the two high-altitude animals are different possibly because of the differences of habitats and habits.