Expression of AQP-1 and AQP-4 in Rat Stomach: An Immunohistochemical Study

Kim, Seung Il

Abstract

PURPOSE: Aquaporins (AQPs) are a family of transmembrane proteins that function as molecular water channels. In mammalian stomach, including human, a large quantitiy of gastric juice is secreted, so water channels are probably involved in its exocrine function. However, little is known about the expression of AQPs in stomach. The purpose of this study was to establish the distribution of AQP-1, AQP-2, AQP-3, and AQP-4 in rat stomach.
METHODS
Stomachs of Sprague-Dawley rats, weighing 200 to 250g, were preserved with a periodate-lysine-paraformaldehyde solution and processed for immunohistochemical studies using ABC method. Rabbit polyclonal antibodies to AQP-1, AQP-2, AQP-3, or AQP-4 were used to identify the water channels. To identify the pericyte and smooth muscle in the vascular wall, mice monoclonal antibody to alpha-smooth muscle actin (ASMA) was used. Parietal cells were identified using an rabbit polyclonal antibody against the H+/-K+/-ATPase.
RESULTS
In this study, we demonstrate distinct distributions of AQP-1 and AQP-4 in rat stomach. AQP-1 is present in apical and basolateral membranes of endothelial cells of lymphatic capillary. AQP-4 is restricted to basolateral membranes of parietal cells located in the glandular base. Whereas, there is no AQP-4 immunoreactivity in the parietal cells of isthmus/neck region. No immunoreactivity for AQP-2 or AQP-3 was observed in rat stomach.
CONCLUSION
These results suggest that AQP-1 is involved in transcellular water transport in the endothelium of lymphatic capillary, and AQP-4 is a major water channel involved in acid secretion in rat stomach.