Intracellular calcium concentration of acinar cells in feline tracheal submucosal glands

Abstract

We measured the intracellular free calcium ion concentration [( Ca2+]i) of acinar cells in isolated feline tracheal submucosal glands in response to secretagogues using the Ca2(+)-sensitive fluorescent dye fura-2. The secretagogues included cholinergic, adrenergic agonists, substance P (SP), and vasoactive intestinal polypeptide (VIP) which induce mucus glycoprotein secretion from feline tracheal submucosal glands. Methacholine (MCh) produced a significant increase in [Ca2+]i of up to 9.8 times that of control in a dose-dependent fashion at concentrations of 10(-8) to 10(-3) M. [Ca2+]i increase by MCh reached a peak within 30 s after stimulation and thereafter showed a sustained rise. In Ca2(+)-free medium, MCh produced an initial transient rise, which was less than 30% of that in a Ca2(+)-containing solution, and which lasted for 60 s with no prolonged sustained rise in [Ca2+]i. Atropine abolished MCh-evoked [Ca2+]i increase. Phenylephrine and SP produced a prolonged increase in [Ca2+]i without an initial transient increase. Phenylephrine (up to 10(-4) M) evoked an increase in [Ca2+]i by up to 240% that of control, which was abolished by prazosin. SP (up to 10(-4) M) also evoked an increase in [Ca2+]i by 155% that of control, which was abolished by atropine. By contrast, both isoproterenol (up to 10(-5) M) and VIP (up to 10(-5) M) failed to alter [Ca2+]i. These findings indicate that the mucus glycoprotein secretion evoked by muscarinic cholinergic, alpha-adrenergic agonist or SP can be mediated by intracellular Ca2+, whereas that by beta-adrenergic agonists or VIP cannot.