Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding.
Intracellular forms of chylomicrons, very low density lipoprotein (VLDL) and high density lipoprotein (HDL) have previously been isolated from the rat intestine. These intracellular particles are likely to be nascent precursors of secreted lipoproteins. To study the distribution of intracellular apo...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Elsevier
1988-09-01
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| Series: | Journal of Lipid Research |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S0022227520384534 |
| _version_ | 1818650576928374784 |
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| author | A M Magun B Mish R M Glickman |
| author_facet | A M Magun B Mish R M Glickman |
| author_sort | A M Magun |
| collection | DOAJ |
| description | Intracellular forms of chylomicrons, very low density lipoprotein (VLDL) and high density lipoprotein (HDL) have previously been isolated from the rat intestine. These intracellular particles are likely to be nascent precursors of secreted lipoproteins. To study the distribution of intracellular apolipoprotein among nascent lipoproteins, a method to isolate intracellular lipoproteins was developed and validated. The method consists of suspending isolated enterocytes in hypotonic buffer containing a lipase inhibitor, rupturing cell membranes by nitrogen cavitation, and isolating lipoproteins by sequential ultracentrifugation. ApoB and apoA-I mass are determined by radioimmunoassay and newly synthesized apolipoprotein characterized following [3H]leucine intraduodenal infusion. Intracellular chylomicron, VLDL, low density lipoprotein (LDL), and HDL fractions were isolated and found to contain apoB, and apoA-IV, and apoA-I. In the fasted animal, less than 10% of total intracellular apoB and apoA-I was bound to lipoproteins and 7% of apoB and 35% of apoA-I was contained in the d 1.21 g/ml infranatant. The remainder of intracellular apolipoprotein was in the pellets of centrifugation. Lipid feeding doubled the percentage of intracellular apoA-I bound to lipoproteins and increased the percentage of intracellular apoB bound to lipoproteins by 65%. Following lipid feeding, the most significant increase was in the chylomicron apoB and HDL apoA-I fractions. These data suggest that in the fasting state, 90% of intracellular apoB and apoA-I is not bound to lipoproteins. Lipid feeding shifts intracellular apolipoprotein onto lipoproteins, but most intracellular apolipoprotein remains non-lipoprotein bound. The constant presence of a large non-lipoprotein-bound pool suggests that apolipoprotein synthesis is not the rate limiting step in lipoprotein assembly or secretion. |
| first_indexed | 2024-12-17T01:52:25Z |
| format | Article |
| id | doaj.art-3e7470d5c13147c09b079bfcc975091d |
| institution | Directory Open Access Journal |
| issn | 0022-2275 |
| language | English |
| last_indexed | 2024-12-17T01:52:25Z |
| publishDate | 1988-09-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Journal of Lipid Research |
| spelling | doaj.art-3e7470d5c13147c09b079bfcc975091d2022-12-21T22:08:01ZengElsevierJournal of Lipid Research0022-22751988-09-0129911071116Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding.A M Magun0B Mish1R M Glickman2Gastrointestinal Unit, Columbia University College of Physicians and Surgeons, New York, NY 10032.Gastrointestinal Unit, Columbia University College of Physicians and Surgeons, New York, NY 10032.Gastrointestinal Unit, Columbia University College of Physicians and Surgeons, New York, NY 10032.Intracellular forms of chylomicrons, very low density lipoprotein (VLDL) and high density lipoprotein (HDL) have previously been isolated from the rat intestine. These intracellular particles are likely to be nascent precursors of secreted lipoproteins. To study the distribution of intracellular apolipoprotein among nascent lipoproteins, a method to isolate intracellular lipoproteins was developed and validated. The method consists of suspending isolated enterocytes in hypotonic buffer containing a lipase inhibitor, rupturing cell membranes by nitrogen cavitation, and isolating lipoproteins by sequential ultracentrifugation. ApoB and apoA-I mass are determined by radioimmunoassay and newly synthesized apolipoprotein characterized following [3H]leucine intraduodenal infusion. Intracellular chylomicron, VLDL, low density lipoprotein (LDL), and HDL fractions were isolated and found to contain apoB, and apoA-IV, and apoA-I. In the fasted animal, less than 10% of total intracellular apoB and apoA-I was bound to lipoproteins and 7% of apoB and 35% of apoA-I was contained in the d 1.21 g/ml infranatant. The remainder of intracellular apolipoprotein was in the pellets of centrifugation. Lipid feeding doubled the percentage of intracellular apoA-I bound to lipoproteins and increased the percentage of intracellular apoB bound to lipoproteins by 65%. Following lipid feeding, the most significant increase was in the chylomicron apoB and HDL apoA-I fractions. These data suggest that in the fasting state, 90% of intracellular apoB and apoA-I is not bound to lipoproteins. Lipid feeding shifts intracellular apolipoprotein onto lipoproteins, but most intracellular apolipoprotein remains non-lipoprotein bound. The constant presence of a large non-lipoprotein-bound pool suggests that apolipoprotein synthesis is not the rate limiting step in lipoprotein assembly or secretion.http://www.sciencedirect.com/science/article/pii/S0022227520384534 |
| spellingShingle | A M Magun B Mish R M Glickman Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding. Journal of Lipid Research |
| title | Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding. |
| title_full | Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding. |
| title_fullStr | Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding. |
| title_full_unstemmed | Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding. |
| title_short | Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding. |
| title_sort | intracellular apoa i and apob distribution in rat intestine is altered by lipid feeding |
| url | http://www.sciencedirect.com/science/article/pii/S0022227520384534 |
| work_keys_str_mv | AT ammagun intracellularapoaiandapobdistributioninratintestineisalteredbylipidfeeding AT bmish intracellularapoaiandapobdistributioninratintestineisalteredbylipidfeeding AT rmglickman intracellularapoaiandapobdistributioninratintestineisalteredbylipidfeeding |