Extracellular ATP regulation of feline tracheal submucosal gland secretion

The standard patch-clamp technique was employed on enzymatically digested acinar cells of submucosal glands isolated from feline trachea. ATP (-10(-3) M) evoked bidirectional current responses and an initial inward current at -80 mV (Cl- current) was followed by an outward current at 0 mV of membrane potential (K+ current). Isoproterenol (ISO) alone did not evoke any significant current responses. However, ISO augmented the ATP-induced inward and outward currents. A phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, mimicked the augmentation by ISO. [Ca2+]i of acinar cells in isolated gland was measured using a fluorescent dye, fura 2. ATP (-10(-3) M) induced an immediate increase in [Ca2+]i followed by a prolonged plateau, and Ca2+ removal resulted in an initial increase alone without the prolonged phase. ISO also augmented the ATP-evoked increases in [Ca2+]i mainly in the plateau phases. Mucus glycoprotein (MGP) secretion was estimated by measuring trichloroacetic acid-precipitable [3H]glycoconjugates from isolated glands. ATP (-10(-3) M) evoked significant MGP secretion and ISO enhanced the ATP-induced MGP secretion. In contrast, adenosine (-10(-3) M) produced no significant responses in current, MGP secretion, or [Ca2+]i. These findings suggest that 1) P2-receptor stimulation and the resultant [Ca2+]i rise induced both electrolyte and MGP secretions and 2) ATP-induced secretion is enhanced by an adenosine 3',5'-cyclic monophosphate intracellular concentration [cAMP]i-rise after beta-receptor stimulation in airway submucosal glands.