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Fluorescence anisotropy from diphenylhexatriene in rat liver plasma membranes
Abstract:
Rat livers were fractionated to obtain intracellular membrane preparations and a highly purified preparation of bile canaliculi. The fraction containing bile canaliculi was homogenized and subfractionated to give fractions representing fragments of contiguous membrane and of canalicular microvilli. The relative purity and extent of contamination of each preparation was determined. When the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene was incorporated into aliquots of each fraction at the same probe: lipid ratio and the steady-state anisotropy of its fluorescence measured, it was found that the plasma membrane preparations were much more ordered than the intracellular membrane preparations. Of the plasma membrane preparations, that containing the canalicular microvilli was the most ordered, even allowing for any contribution of contaminants. Thus the microvillus membrane of the bile canaliculus appears to be the most ordered domain of the plasma membrane of the hepatocyte. The high order in this domain may be a factor in reducing the susceptibility to bile salt damage during bile secretion, since it is this region which is exposed to high concentrations of bile salts in vivo.
Insights
Hepatocyte plasma membranes, particularly the bile canaliculus microvilli, exhibit higher order than intracellular membranes. This increased order may protect against bile salt damage during secretion.
Area of Science:
- Cell Biology
- Hepatology
- Membrane Biophysics
Background:
- Hepatocytes are the primary cells of the liver, responsible for bile production and secretion.
- Bile canaliculi form a network within the liver that transports bile.
- The structural organization of hepatocyte plasma membranes, especially in bile canaliculi, is crucial for liver function and protection.
Purpose of the Study:
- To investigate the structural order of different hepatocyte membrane domains.
- To compare the order of bile canalicular membranes with intracellular membranes.
- To explore the potential functional implications of membrane order in bile secretion.
Main Methods:
- Rat livers were fractionated to isolate intracellular membranes and bile canaliculi.
- Bile canaliculi were further subfractionated into contiguous membrane and microvilli fractions.
- The fluorescent probe 1,6-diphenyl-1,3,5-hexatriene was used to measure membrane order via fluorescence anisotropy.
Main Results:
- Plasma membrane preparations showed significantly higher order than intracellular membrane preparations.
- The fraction containing canalicular microvilli exhibited the highest degree of membrane order.
- This high order was maintained even after accounting for potential contaminants.
Conclusions:
- The microvillus membrane of the bile canaliculus represents the most ordered domain of the hepatocyte plasma membrane.
- The enhanced order of the bile canalicular microvillus membrane may confer resistance to bile salt-induced damage.
- This structural feature could be a protective mechanism during the high-concentration bile salt environment of bile secretion.