Phosphatidylinositol 4,5-bisphosphate stimulates alveolar epithelial fluid clearance in male and female adult rats

Kooijman EE, Kuzenko SR, Gong D, Best MD, Folkesson HG. Phosphatidylinositol 4,5-bisphosphate stimulates alveolar epithelial fluid clearance in male and female adult rats. Am J Physiol Lung Cell Mol Physiol 301: L804-L811, 2011. First published August 26, 2011; doi:10.1152/ajplung.00445.2010.-Cell membrane phospholipids, like phosphatidylinositol 4,5-bisphosphate [PI(4,5)P-2], can regulate epithelial Na channel (ENaC) activity. Gender differences in lung ENaC expression have also been demonstrated. However, the effects in vivo on alveolar fluid clearance are uncertain. Thus PI(4,5)P-2 effects on alveolar fluid clearance were studied in male and female rats. An isosmolar 5% albumin solution was intrapulmonary instilled; alveolar fluid clearance was studied for 1 h. Female rats had a 37 +/- 19% higher baseline alveolar fluid clearance than male rats. Bilateral ovariectomy attenuated this gender difference. Compared with controls, PI(4,5)P-2 instillation (300 mu M) increased alveolar fluid clearance by similar to 93% in both genders. Amiloride or the specific alpha ENaC small-interfering RNA inhibited baseline and PI(4,5)P-2-stimulated alveolar fluid clearance in both genders, indicating a dependence on amiloride-sensitive pathways. The fraction of amiloride inhibition was greater in PI(4,5)P-2-instilled rats (male: 64 +/- 10%; female: 70 +/- 11%) than in controls (male: 30 +/- 6%; female: 44 +/- 8%). PI(4,5)P-2 instillation lacked additional alveolar fluid clearance stimulation above that of terbutaline, nor did propranolol inhibit alveolar fluid clearance after PI(4,5)P-2 instillation, indicating that PI(4,5)P-2 stimulation was not secondary to endogenous beta-adrenoceptor activation. PI(4,5)P-2 amine instillation resulted in an intermediate alveolar fluid clearance stimulation, suggesting that, to reach maximal alveolar fluid clearance stimulation, PI(4,5)P-2 must reside in cell membranes. In summary, PI(4,5)P-2 instillation upregulated in vivo alveolar fluid clearance similar to short-term beta-adrenoceptor upregulation of alveolar fluid clearance. PI(4,5)P-2 stimulation was mediated partly by increased amiloride-sensitive Na transport. There exist important gender-related effects suggesting a female advantage that may have clinical implications for resolution of acute lung injury.