Kidney and heart have a typical combination of monocarboxylate transporter and l
ID: 261724 • Letter: K
Question
Kidney and heart have a typical combination of monocarboxylate transporter and lactate dehydrogenase isofroms for a "consumer" of lactate, i.e. MCT 1 and LDH-H?4?. Liver however has what might seem like mismatched isoforms, i.e. ?MCT 1 and LDH-M4.
??(i) Explain how kidney and heart act as "consumers" of lactate, including an explanation of why MCT 1 and LDH-H4 ?would be the expected isoforms for a "consumer" of lactate. (ii) Explain the role of liver in lactate metabolism, why the liver combination of MCT 1 and LDH-M4 ?might be considered a mismatch, and outline why this apparent mismatch might make sense in terms of the liver's role in lactate metabolism.
Explanation / Answer
Please find the answers below:
Answer i) The lactate metabolism remains one of the major sources of energy that too very frequently in the cells. Particularly, there are two major modes of respiration, aerobic and anaerobic. Whereas aerobic respiration generates more energy per unit substrate, it requires the presence of oxygen. On the other hand, the anaerobic respiration is very quick in nature and does not require much oxygen to take place but generates lesser amount of energy comparatively. Lactate metabolism remains one such mechanism. The kidneys and the heart remain among the major organs where lactate metabolism takes place. The renal cortex and the myocardium are routinely engaged in lactate metabolism since they required large amount of uninterrupted supply of enery and hence, it is very necessary that they are equipped with alternative sources of energy as compared to aerobic respiration. In this regard, these organs have evolutionarily evolved with specific receptors on their cellular surfaces for intake of lactate. The combination of these receptors allow these organs to specifically enter the lactate into their cells and consequent metabolism. The spent lactate and its by-products are continuously released from the heart myocardium and the renal cortex into the circulation and renal filtrate. Thus, presence of this combinatorial receptors is mandatory for lactate uptake and metabolism.
Answer ii) The liver is countinously engaged in lactate metabolism. Liver remains not only the location for metabolism but also eliminates the toxic wastes from the body. Particularly, the Cori's nitrogen cycle is operated in the hepatocytes which switches between cellular lactate and hepatic glucose generation so that uninterrupted supply of energy might be ensured in the body. In order to ensure this, the liver also contains specific hepatocyte receptors for lactate and glucose which are sensitive to circulating levels of these biomolecules. Hence, the mismatch of these receptors on the liver actually accounts for recycling of the raw materials for generation of energy by either aerobic or anaerobic respiration in the body.
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