ISOPROTERENOL AUGMENTS ATP-EVOKED CL- SECRETION ACROSS CANINE TRACHEAL EPITHELIUM

Using an Ussing chamber, both the posterior epithelial membrane and cu ltured epithelial cell monolayers from canine trachea were used for me asurements 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 increas e in SCC in a dose-dependent fashion, reaching a peak value within 3 m in 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, pretreatme nt with 10(-8) M ISOP significantly augmented the ATP-induced SCC rise , whereas G did not significantly change. These findings indicate that beta-adrenergic stimulation augments Cl- secretion induced by P-2-rec eptor stimulation in airway epithelial cells.