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Edit Toth-Molnar, Orsolya Berczeli, Vizvari Eszter, Zoltan Rakonczay, Peter Hegyi, Chuanqing Ding; Effect of vasoactive intestinal peptide on lacrimal gland ductal fluid secretion in wild type and CFTR knockout mice. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2242. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Earlier reports demonstrated the presence of vasoactive intestinal peptide (VIP) receptors in the lacrimal gland (LG) and the role of VIP in acinar protein secretion. However, it is unknown whether VIP has any effect on fluid secretion of LG ducts. Recently, we reported that cystic fibrosis transmembrane conductance regulator (CFTR) plays a key role in LG ductal fluid secretion. There are accumulating evidences that VIP stimulation and CFTR functions are tightly related and regulated. Therefore the aim of the present study was to investigate the VIP-mediated fluid secretion of isolated LG ducts from wild type (WT) and CFTR knockout (CFTR KO) mice.
Immunofluorescence was used to confirm the presence of VIP receptors on LG duct cells. LG interlobular and intralobar ducts were isolated from WT and CFTR KO mice as we described earlier. Ends of the ducts seal during incubation, forming a closed luminal space. The secretory response can be analyzed using bright field video-microscopy. Effects of VIP (100 nM) on ducts from WT and CFTR KO mice were investigated. As VIP acts not only through the adenylyl cyclase-cAMP system but - in a smaller extent - through the elevation of cytosolic Ca2+ level ([Ca2+]i}, intracellular Ca2+ homeostasis underlying VIP stimulation was also measured with fluorophotometry using the Ca2+-sensitive fluorescent dye Fura 2-AM. Data was presented as means ± SEM.
Immunofluorescence proved the presence of VPAC1 and VPAC2 receptors on the basolateral membranes of mouse LG duct cells. VIP stimulation caused a strong and continuous fluid secretion in WT mouse LG ducts (secretory rate: 213.1 ± 37.3 pl/min/mm2, n=7). In contrast, CFTR KO ducts exhibited only a weak pulse-like secretion in the first 5 minutes of stimulation (54.5 ± 18.4 pl/min/mm2, n=6), followed by a plateau phase. VIP stimulation resulted in a statistically significant increase in [Ca2+]i both in WT (24.01 ± 9.07%, p=0.001) and in CFTR KO ducts (22.04 ± 9.12%, p=0.002).
Our results reveal new insight into the role of VIP in LG duct function by demonstrating VIP-induced fluid secretion of mouse LG duct segments. Role of CFTR in the secretory process found to be decisive as only small VIP-induced fluid secretion was detected in the absence of CFTR protein. The weak fluid secretory response evoked by VIP in CFTR KO ducts may reflect the elevation of [Ca2+]i observed.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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