Characteristics and physiological role of surfactant-like particles secreted by entrocytes.

Intestinal epithelium secretes novel unilamellar membranes having characteristics similar to lung surfactants and thus has been named Surfactant-like particles (SLP). The chemical analysis of the membranes revealed cholesterol/phospholipid molar ratio of 0.68-0.78, which is much distinct from that of the underlying microvillus membranes (1.34-1.49). The membrane contains 4-6 proteins with a molar weight of 30-120 kDa and is enriched with alkaline phosphatase, contains low amounts of disaccharidases but no Na+, K(+)-ATPase activity. The secretion of SLP is stimulated by fat feeding. Chronic ethanol ingestion also induces the formation of SLP in rat intestine. A number of physiological functions have been attributed to SLP, which include: (i) as a protective lubricant in intestinal lumen, (ii) a role in triacylglycerol transport, (iii) as a vehicle for the transport of luminal proteins into blood, (iv) as a stratum for the adhesion of microorganisms in intestinal lumen, and (v) a role in trans-signalling mechanism across the basolateral surface of enterocytes.