Role of the Phospholipase C Pathway and Calcium Mobilization in Oxytocin-Induced Contraction of Lacrimal Gland Myoepithelial Cells

PURPOSE: We reported that oxytocin (OXT), added to freshly prepared lacrimal gland lobules, induced myoepithelial cell (MEC) contraction. In other systems, OXT activates phospholipase C (PLC) generating Inositol 1,4,5-trisphosphate (IP(3)) which increases intracellular calcium concentration ([Ca(2+)](i)) causing contraction. The aim of the current study was to investigate the role of this pathway in OXT-induced contraction of MEC. METHODS: Tear volume was measured using the cotton thread method. Lacrimal gland MEC were isolated and propagated from α-smooth muscle actin (SMA)-green fluorescent protein (GFP) mice, in which MEC express GFP making them easily identifiable. RNA and protein samples were prepared for RT-PCR and Western blotting for G protein expression. Changes in [Ca(2+)](i) were measured in Fura-2 loaded MEC using a ratio imaging system. MEC contraction was monitored in real time and changes in cell size were quantified using ImageJ software. RESULTS: OXT applied either topically to surgically exposed lacrimal glands or delivered subcutaneously resulted in increased tear volume. OXT stimulated lacrimal gland MEC contraction in a dose-dependent manner, with a maximum response at 10(−7) M. MEC express the PLC coupling G proteins, Gαq and Gα11, and their activation by OXT resulted in a concentration-dependent increase in [Ca(2+)](i) with a maximum response at 10(−6) M. Furthermore, the activation of the IP(3) receptor to increase [Ca(2+)](i) is crucial for OXT-induced MEC contraction since blocking the IP(3) receptor with 2-APB completely abrogated this response. CONCLUSIONS: We conclude that OXT uses the PLC/Ca(2+) pathway to stimulate MEC contraction and increase lacrimal gland secretion.