Meshell Johnson, MD

Lung fluid balance is critical for efficient gas exchange.  Alveolar flooding, which may occur in many different pathological states, disturbs normal lung fluid balance, impairs gas exchange, and can lead to significant morbidity and mortality. Fluid balance is governed by ion transport across the alveolar epithelium, which lines more than 99% of the internal surface area of the lung and is composed of alveolar type I and type II cells.  Type II cells, which cover 2-5% of the surface area, have been extensively studied and are known to contain ion transport proteins.  Type I cells, which cover the remaining 95% of the internal surface area, have been less well characterized, but were long thought to not be involved in ion transport. Thus the general theory of ion and fluid movement in the lung was that type II cells governed ion transport while type I cells merely provided a route for passive water movement.  Our research focuses on the study of ion and fluid transport in the lung, with an emphasis on ion transport in alveolar type I cells. We have demonstrated that type I cells functionally transport ions, necessitating modification of the current paradigm of ion and fluid transport in the lung to now state that ion transport occurs across the entire alveolar surface, rather than being limited to type II cells.

Our research goals are to continue the characterization of Na+ and Cl- transport in type I cells, determine what factors modulate ion transport in type I cells, and attempt to elucidate the specific contribution of type I and type II cells to total ion and fluid transport in the lung. Better understanding of how the lung maintains and regulates fluid balance will help delineate the mechanisms that regulate alveolar fluid balance and may lead to strategies to prevent or treat the respiratory compromise associated with alveolar flooding.