α1-Adrenoceptors relate Ca2+ modulation and protein secretions in rat lacrimal gland

Abstract

Noradrenaline (NA) is a catecholamine with multiple roles including as a hormone and a neurotransmitter. Cellular secretory activities are enhanced by adrenergic stimuli as well as by cholinergic stimuli. The present study aimed to determine which adrenoceptors play a role in controlling intracellular calcium ion ([Ca2+]i) level in acinar cells of rat lacrimal glands. Expression of mRNA for adrenoceptor subtypes in the acinar cells was assessed using RT-PCR. All types except α2c, β1, and β3 were detected. NA induced a [Ca2+]i increase with a biphasic pattern in the acinar cells. Removal of extracellular Ca2+ and use of Ca2+-channel blockers did not inhibit the NA-induced [Ca2+]i increases. In contrast, U73122 and suramin almost blocked these increases. The α1- adrenoceptor agonist phenylephrine induced a strong increase in [Ca2+]i. However, clonidine and isoproterenol failed to induce a [Ca2+]i increase. The peroxidase activity was quantified as a measure of mucin secretion. Ca2+-dependent exocytotic secretion of peroxidase was detected in rat lacrimal glands. The RT-PCR results showed that MUC1, MUC4, MUC5AC, MUC5B, and MUC16 were expressed in acinar cells. These findings indicated that NA activates α1-adrenoceptors, which were found to be the main receptors in Ca2+-related cell homeostasis and protein (including mucin) secretion in lacrimal glands.