Abstract
Conditions were developed for rapid deposition of triglyceride in isolated rat hepatocytes. Liver cells from fasted rats were incubated for 90 min at 37 degrees C with 3.0 mM palmitic or oleic acid, 4% bovine serum albumin, 20 mM glucose, 10 mM lactate, and 1 mM pyruvate. When oleic acid was used, numerous cytoplasmic lipid droplets were produced. When hepatocytes were incubated with palmitic acid, similar amounts of triglyceride were synthesized but instead of lipid droplets, a vast accumulation of peculiar spicules permeated the cytoplasm. These inclusions appeared in myriads of swirled threads, thick elongated angular plates, and needles, some of which exhibited longitudinal osmiophilic bands of 250 A thickness. These structures were associated with smooth endoplasmic reticulum. The cells appeared otherwise normal. Polarized light microscopy at 37 degrees C revealed a multiplicity of brilliant white inclusions between crossed polars in cells incubated with palmitic acid. These birefringent structures exhibited 90 degrees periodicity between both maximum brilliance and extinction, indicative of anisotropic crystalline deposits. Molecular species analysis of triglycerides in cells incubated with palmitic acid, together with data on [1-14C]palmitic acid incorporation, demonstrated an almost exclusive synthesis of tripalmitin. Spicules isolated from homogenized hepatocytes displayed needles containing longitudinal single and double osmiophilic bands of 110 A and 260 A thickness, respectively, and lipid spicular aggregates. The isolated spicules were almost pure tripalmitin by analysis. These observations document the formation and development of crystalline triglyceride in living cells and may provide a unique system for the study of cellular lipid synthesis, transport and deposition.
Highlights
Conditions were developed for rapid deposition of triglyceride in isolated rat hepatocytes
In the course of experiments designed to cause the acute accumulation of lipid droplets in hepatocytes, we incubated isolated liver cells with high concentrations of long chain fatty acids together with antiketogenic substrates to inhibit fatty acid oxidation and promote triglyceride synthesis
The observed accumulation of triglyceride radioactivity averaged 45,590 dpm/mg dry wt, which demonstrates incorporation of 193 nmol of palmitic acid. This is equivalent to 64 nmol of triglyceride, in close agreement with the observed increase in triglyceride mass. These results indicate the predominant synthesis of tripalmitin
Summary
Conditions were developed for rapid deposition of triglyceride in isolated rat hepatocytes. When hepatocytes were incubated with palmitic acid, similar amounts of triglyceride were synthesized but instead of lipid droplets, a vast accumulation of peculiar spicules permeated the cytoplasm These inclusions appeared in myriads of swirled threads, thick elongated angular plates, and needles, some of which exhibited longitudinal osmiophilicbands of 250 A thickness. In the course of studies on the metabolism of triglyceride-rich lipid droplets in isolated rat hepatocytes, we noticed a plethora of peculiar crystalline-like structures dispersed throughout the cytoplasm when the cells were incubated with palmitic acid under conditions of rapid triglyceride synthesis. This synthetic process occurs in the outer leaflet of the endoplasmic reticulum bilayer [13]. The present communication describes the formation, ultrastructure, and chemistry of these unusual lipid deposits
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
