Protein kinase C activity during the process of lung liquid clearance

Although active transport of sodium plays an important role in the resolution of pulmonary edema, the biochemical regulation of this process is still under investigation. The purpose of this study was to evaluate the activity of protein kinase C during the process of lung liquid clearance. Alveolar flooding was induced by instilling 5% bovine serum albumin solution, saline, or heterologous serum in the air spaces of rats. The activity of protein kinase C was measured in both the instilled and control lungs at 10 min and 1 and 4 h after fluid instillation. Four hours after instillation of 5% bovine serum albumin, the ratio of protein kinase C activity in the instilled lung compared with the control lung was 2.2 +/- 0.3. Similar results were obtained following instillation with heterologous serum or saline. Since we measured a clearance rate of 0.8 ml/h in anesthetized rats, we can postulate that the activation of protein kinase C occurred when > 40% of the liquid had been cleared from the lung. This increased activity of protein kinase C was not due to an increase in kinase activity in the inflammatory cells or an increase in enzyme quantity but due to a decrease of protein kinase C inhibitory activity in the lung. These results suggest that protein kinase C second messenger system may play a regulatory role in lung liquid clearance.