Isoproterenol augments ATP-evoked Cl^- secretion across canine tracheal epithelium

Using an Ussing chamber, both the posterior epithelial membrane and cultured epithelial cell monolayers from canine trachea were used for measurements of potential difference (PD) and short circuit current (SCC). Conductance (G) was calculated as the ratio SCC PD. Adenosine (10^-5 to 10^-3 M) failed to produce any significant increases in PD and SCC. ATP (10^-6 to 10^-4 M) produced a significant transient increase in SCC in a dose-dependent fashion, reaching a peak value within 3 min after stimulation. Isoproterenol (ISOP) at 10^-8 M itself did not significantly alter the SCC value. In both the epithelial membrane and cultured epithelial cells treated with amiloride, however, pretreatment with 10^-8 M ISOP significantly augmented the ATP-induced SCC rise, whereas G did not significantly change. These findings indicate that β-adrenergic stimulation augments Cl^- secretion induced by P₂-receptor stimulation in airway epithelial cells.