Distinct contributions by ionotropic purinoceptor subtypes to ATP-evoked calcium signals in mouse parotid acinar cells

摘要

There is emerging consensus that P2X 4 and P2X 7 ionotropic purinoceptors (P2X 4R and P2X 7R) are critical players in regulating [Ca 2+] i dynamics and fluid secretion in the salivary gland. In contrast, details regarding their compartmentalization and selective activation, contributions to the spatiotemporal properties of intracellular signals and roles in regulating protein exocytosis and ion channel activity have remained largely undefined. To address these concerns, we profiled mouse parotid acinar cells using live-cell imaging to follow the spatial and temporal features of ATP-evoked Ca 2+ dynamics and exocytotic activity. Selective activation of P2X 7Rs revealed an apical-to-basal [Ca 2+] i signal that initiated at the sub-luminal border and propagated with a wave speed estimated at 17.3 ± 4.3 μm s -1 (n= 6). The evoked Ca 2+ spike consisted of Ca 2+ influx and Ca 2+-induced Ca 2+ release from intracellular Ca 2+ channels. In contrast, selective activation of P2X 4Rs induced a Ca 2+ signal that initiated basally and propagated toward the lumen with a wave speed of 4.3 ± 0.2 μm s -1 (n= 8) that was largely independent of intracellular Ca 2+ channel blockade. Consistent with these observations, P2X 7R expression was enriched in the sub-luminal regions of acinar cells while P2X 4R appeared localized to basal areas. In addition, we showed that P2X 4R and P2X 7R activation evokes exocytosis in parotid acinar cells. Our studies also demonstrate that the P2X 4R-mediated [Ca 2+] i rise and subsequent protein exocytosis was enhanced by ivermectin (IVR). Thus, in addition to furthering our understanding of salivary gland physiology, this study identifies P2X 4R as a potential target for treatment of salivary hypofunction diseases.