Keeping Lung Surfactant Where it Belongs: Protein Regulation of Two-Dimensional Viscosity

¹ University of California, Santa Barbara
² Research and Education Institute
³ Univ. of California

^* To whom correspondence should be addressed. E-mail: gorilla{at}engineering.ucsb.edu.

Submitted on August 30, 2004
Revised on December 5, 2004
Accepted on 2 March 2005

	Abstract

Lung surfactant causes the surface tension, , in the alveoli to drop to nearly zero on exhalation; in the upper airways ~ 30 mN/m and constant. Hence, a surface tension gradient exists between alveoli and airways that should lead to surfactant flow out of the alveoli and elimination of the surface tension gradient. However, the lung surfactant specific protein SP-C enhances the resistance to surfactant flow by regulating the ratio of solid to fluid phase in the monolayer, leading to a jamming transition, at which the monolayer transforms from fluid-like to solid-like. The accompanying 3 orders of magnitude increase in surface viscosity helps minimize surfactant flow to the airways, and likely stabilizes the alveoli against collapse.

Key Words: jamming, surface tension, surface viscosity, surfactant protein B, surfactant protein C

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