The Influence Of β-adrenoceptor Activity On Na~+ Channel In Alveolar Epithelium

Besides of the gas exchanging function, alveolar epithelial tissue vitally functions to maintain the alveolar liquid environment in the respiratory system. Research revealed that the alveolar liquid clearance mainly depends on the Na~+ transport mediated by alveolar epithelial Na~+ channels (ENaC).β-adrenoceptor agonists are currently used to dissipate alveolar edema effectively in clinic. However, many unknown aspect needs to be explored in cellular mechanism underlying sodium and water transport affected byβ-zdrenoceptor agonists.In this study,β-adrenoceptor agonist isoprenaline, antagonist propranolol andα- adrenoceptor antagonist phentolaming were used to human lung adenocarcinoma cell line A549 and human epithelial cell line 16HBE. RT-PCR method was used to measure the mRNA expressing changes ofβ-receptor and epithelial sodium channelα,βandγsubunits. The results showed that isoprenaline could enhance the mRNA expression ofβ-receptor and ENaC-βand–γsubunits in alveolar A549 cell line, and could reduce the mRNA expression of ENaC-βand–γsubunits in airway 16HBE cell line.β-adrenoceptor antagonist propranolol could reduce ENaC-βand-γmRNA expression in 16HBE, suggesting thatβ-receptor agonists and antagonists could regulate the expression of ENaC in cells by alteringβ-receptor expression. The effect ofα–adrenoceptor antagonist phentolamine on the two cell lines, is similar to that of isoprenaline, increased the expression of ENaC-βand–γsubunits in A549 and decreased the expression in 16HBE. We also investigated the culture condition of collagen substratum, cell seeding density, cell growing time and established the tight monolayer of A549 and 16HBE cell. Electrophysiolgical short-circuit current technique was used to primarily study the ion transport across cellular monolayer of both A549 and 16HBE. The agonist adrenaline stimulated increase of short-circuit current and Cl- channel agonists forskolin and ATP stimulated the increase of short-circuit current, suggesting the activity of ion transport mediated by Na~+ and Cl- channels.This study revealed that agonist/antagonist were able to influence mRNA expression ofβ-receptor and Na~+ channels, demonstrating that, in alveolar and airway epithelial cells,β-receptor agonist/antagonist could regulate the expression of ENaC by influencing expression ofβ-receptor, and achieve the regulation of alveolar liquid clearance. The results also showed that the sameβ-adrenoceptor agonist could cause different expressing results in alveolar and airway epithelial cells, suggesting that evident differences on ion transport function between two cell types. The primarily established filter-supporting culture method with A549 and 16HBE cells provided an experimental basis for further study on ion transport and cellular/molecular mechanisms.