Salinity effects on differential expression of lactate dehydrogenase in the liver and muscle of milkfish when acclimated to hypothermal environments

• Main Authors: Xiu-Wei Zhou, 周修緯
• Other Authors: Tsung-Han Lee
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/33829013736714512449

碩士 === 國立中興大學 === 生命科學系所 === 103 === The euryhaline milkfish (Chanos chanos) is one of the economically important aquaculture teleosts in Taiwan. However, in winter, the cold snap usually cause mass mortality of the cultured milkfish and resulted in severe economic loss of the fishermen. When acclimated to changes in environmental temperatures or salinities, sufficient energy was required through regulating aerobic and anaerobic metabolic pathways to maintain physiological functions. Lactate dehydrogenase (LDH), a tetrameric enzyme, was encoded by two structurally distinct genes, ldha and ldhb. LDH was involved in anaerobic metabolism to facilitate the production of ATP. The lactate dehydrogenase were found to have different functions include LDH-oxidase (LDH-O) and LDH-reductase (LDH-R) activity, that capacity for oxidation of lactate and reduction of pyruvate, respectively. The present study, examined the blood glucose and liver and muscle LDH functions were determined in seawater (SW)- or fresh water (FW)- acclimated milkfish when exposed to hypothermal environments. The blood glucose levels significantly increased in the hypothermal SW-acclimated milkfish. On the contrary, the low blood glucose were found in the FW group. The mRNA abundance of ldhb was expressed mainly in the red muscle, while in white muscle was ldha. The results of this study demonstrated the patterns of ldhb and LDH-O activity in the liver of FW-acclimated milkfish remained compensation for the metabolic rate at lower temperature, while the metabolic rate was reduced in the SW group. Meanwhile, the results indicated that LDH-R activity in red muscle and white muscle of SW-acclimated and FW-acclimated milkfish compensated for anaerobic metabolism for adaption to low-temperature environment. On the other hand, the mRNA levels of monocarboxylate transporter 1 (mct1) in the liver of SW/18°C and FW/18°C milkfish indicated their roles in lactate uptake in the liver. The liver expressed glucose transporter 2 (glut2) to maintain constant blood glucose level at 18 °C. Taken together, the present study inferred that when milkfish were acclimated to hypothermal environments, the lactate produced form muscles through anaerobic metabolism might be converted to blood glucose through the liver.