Mechanical forces modulate alveolar epithelial phenotypic expression.

Physical forces play an important role in modulating lung development, growth, compliance, differentiation and metabolism. Both tonic distension and phasic changes in volume occur during development and after birth. Morphometric studies have shown that alveolar epithelial cells are distended during lung expansion from functional residual capacity. In both in vivo and in vitro model systems, mechanical distension stimulates surfactant secretion. Drawing on the results of developmental anomalies and experiments in vivo, we and others have generated the underlying hypothesis that mechanical distension promotes expression of the type I cell phenotype and inhibits expression that of the type II; contraction has the opposite effects. The results of recent experiments, using both cultured type II cells from adult rodents and fetal lung explant tissue to test this hypothesis, provide support. The molecular and biochemical mechanisms by which physical forces affect lung functions are currently under investigation.