#hepatocytes

Membrane Transportation

Which ABC transporter plays a role in cholesterol and phospholipid transport in hepatocytes?

Row labeled Q30 appears truncated but query addresses which ABC transporter handles cholesterol and phospholipid transport in hepatocytes. In canalicular membrane ABCB4 MDR3 is established phosphatidylcholine floppase essential for biliary phospholipid secretion, pairing with bile salt export via ABCB11 and cholesterol export via ABCG5/G8. Its ATP-driven flipping of phosphatidylcholine to outer leaflet allows bile acids to extract lipid into mixed micelles that solubilize cholesterol and buffer bile acid detergent toxicity. At sinusoidal membrane, ABCA1 effluxes cholesterol and phospholipid to apolipoprotein A1 forming nascent HDL, contributing to reverse cholesterol transport. ABCB1 MDR1 exports amphipathic drugs xenobiotics rather than bulk biliary lipids, while SGLT1 and SGLT2 are sodium-glucose cotransporters secondary active members of SLC5 family irrelevant to lipid secretion. Clinically ABCB4 defects produce low-phospholipid bile, cholestasis, cholelithiasis and progressive liver injury, highlighting distinct partitioning of lipid transport functions among hepatic ABC proteins for bile formation and systemic lipoprotein metabolism. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.

Ref: Borst et al., Annu Rev Biochem 2000, ABC transporters in lipid transport; Alberts, Chapter 11.

View Details

Membrane Transportation

Which ABC transporter plays a role in cholesterol and phospholipid transport in hepatocytes?

Cholesterol and phospholipid homeostasis in hepatocytes involves coordinated action of several ABC transporters at canalicular membrane. ABCB4 MDR3 flips phosphatidylcholine from inner to outer leaflet making it available for bile salt extraction forming mixed micelles that protect biliary epithelium and solubilize cholesterol exported by ABCG5/G8 heterodimer. ABCB1 MDR1 primarily exports hydrophobic xenobiotics and drugs, not bulk phospholipid for bile formation, though it can translocate short-chain lipids in vitro. ABCA1, not listed among options but relevant, mediates phospholipid and cholesterol efflux to apolipoprotein A1 for nascent HDL biogenesis at basolateral side. SGLT family members SLC5A1 and SLC5A2 are sodium-glucose symporters secondary active, unrelated to lipid transport. Mutations in ABCB4 cause progressive familial intrahepatic cholestasis type 3 with low biliary phospholipid, cholangitis and cholelithiasis, while ABCG5/G8 defects cause sitosterolemia, demonstrating specific partitioning of cholesterol and phosphatidylcholine pathways among distinct ABC transporters in liver physiology and disease. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.

Ref: Oude Elferink & Paulusma 2007, Hepatic lipid transporters; Nicolaou et al., J Hepatol 2012.

View Details

Membrane Transportation

Which transporter regulates bile phospholipid transport in hepatocytes?

Phosphatidylcholine supply to bile is governed by canalicular ABC transporter ABCB4, also known as multidrug resistance protein 2 or 3 in rodents and humans. This ATP-driven floppase actively translocates endogenous phosphatidylcholine from inner cytoplasmic leaflet to outer exoplasmic leaflet of hepatocyte canalicular membrane. Bile salts secreted via ABCB11 then extract phospholipid into bile forming mixed micelles that solubilize cholesterol and shield ductal epithelium from detergent toxicity of bile acids. ABCB1 MDR1 contributes to hydrophobic xenobiotic efflux but does not move bulk phosphatidylcholine for bile; Na+/K+ ATPase generates sodium gradient but does not directly handle biliary lipids; GLUT family facilitators transport monosaccharides, not phospholipids. Mutations in ABCB4 cause progressive familial intrahepatic cholestasis type 3 and low-phospholipid-associated cholelithiasis, linking transporter dysfunction to gallstone disease, fibrosis and cholestasis, illustrating specific regulation of biliary lipid composition by dedicated floppase rather than generic drug exporter. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.

Ref: Oude Elferink & Paulusma, Pflugers Arch 2007, ABCB4 phosphatidylcholine transport.

View Details

Immunology

Acute phase proteins are mainly produced by

Hepatocytes, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

View Details