Distribution and content of microtubules in relation to the transport of lipid. An ultrastructural quantitative study of the absorptive cell of the small intestine.

Abstract

To determine whether microtubules are linked to intracellular transport in absorptive cells of the proximal intestine, quantitative ultrastructural studies were carried out in which microtubule distribution and content were determined in cells from fasting and fed animals. Rats were given a 1-h meal of standard chow, and tissue was taken from the mid-jejunum before, 1/2 h and 6 h after the meal. The microtubule content of apical, Golgi and basal regions of cells was quantitated by point-counting stereology. Microtubules apparently were localized in intracellular regions of enterocytes (apical and Golgi areas) previously shown to be associated with lipid transport and the microtubule content within apical and Golgi regions was significantly (P < 0.01) reduced during transport of foodstuffs. To determine the effect of inhibition of microtubule assembly on transport, colchicine or vinblastine sulfate was administered to postabsorptive rats and the lipid and microtubule content of enterocytes determined 1 and 3 h later. After treatment with these agents, lipid was found to accumulate in apical regions of cells; this event was associated with a significant reduction in microtubule content. Regional distribution of microtubules in enterocytes, decrease in assembled microtubules after a fat-containing meal and accumulation of lipid after administration of antimicrotubule agents suggest that microtubules are related to lipid transport in enterocytes.