Synthesis and secretion of apolipoproteins by pig intestinal mucosa in organ culture: lack of inhibition of apolipoprotein A-I secretion by colchicine

Abstract 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. [ 14 C]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 M r 45000, most likely apolipoprotein A-IV, representing about 3.5% of newly secreted proteins. The d > 1.21 fractions all contained a high M r protein, identified as IgA, and an unidentified protein of M r approximately 45000. The addition of colchicine (125 μM) to the culture medium did not significantly modify either tissue enzyme activities or [ 14 C]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 it which is secreted free.