Synthesis and secretion of apolipoproteins by pig intestinal mucosa in organ culture. Lack of inhibition of apolipoprotein A-I secretion by colchicine.
Pig duodeno-jejunal mucosa was maintained in organ culture for up to 24 h in Eagle's minimum essential medium containing 10% foal serum. Viability was controlled by determination of alkaline phosphatase and sucrase activity in the tissue. [14C]Leucine incorporation into proteins decreased 3-fold between 2 and 24 h. Newly synthesized secreted proteins were analyzed by SDS-polyacrylamide gel electrophoresis of the whole culture medium. Apolipoprotein A-I specifically measured by immunoelectrophoresis represented 10-20% of newly secreted proteins. Only 10% of apolipoprotein A-I secreted was recovered with the lipoprotein fraction (d less than 1.21). Recombination of the medium with porcine lipoproteins or DMPC vesicles prior to ultracentrifugation allowed, respectively, the recovery of 40 and 80% of apolipoprotein A-I secreted. The lipoprotein fractions also contained some apolipoproteins B and C and, after DMPC recombination, an apolipoprotein of Mr 45 000, most likely apolipoprotein A-IV, representing about 3.5% of newly secreted proteins. The d greater than 1.21 fractions all contained a high Mr protein, identified as IgA, and an unidentified protein of Mr approximately 45 000. The addition of colchicine (125 microM) to the culture medium did not significantly modify either tissue enzyme activities or [14C]leucine incorporation. It reduced total secretion by about 40% between 2 and 8 h of incubation, without interfering with apolipoprotein A-I secretion, which then represented up to 35% of secretion products. This raises the question of the mode of secretion of apolipoprotein A-I, which may be related to the high proportion of its which is secreted free.
D000818:Animals; D016632:Apolipoprotein A-I; D001053:Apolipoproteins / Q000096:biosynthesis / Q000378:metabolism*; D003078:Colchicine / Q000494:pharmacology*; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D007122:Immunoelectrophoresis; D007413:Intestinal Mucosa / Q000378:metabolism*; D008074:Lipoproteins / Q000096:biosynthesis; D009924:Organ Culture Techniques; D014176:Protein Biosynthesis; D013552:Swine
D016632:Apolipoprotein A-I; D001053:Apolipoproteins; D008074:Lipoproteins; D003078:Colchicine; D004134:Dimyristoylphosphatidylcholine