![ionic activation bypass ionic activation bypass](https://proserialkeys.com/wp-content/uploads/2020/10/3052246_iTools-2015.png)
SMGs secrete mainly mucus, HCO 3 – and growth factors, and their primary function is to lubricate the oesophagus and to protect it from the damaging effects of the refluxed acid. The submucosal glands (SMGs) are tubuloacinar glands that occur scattered throughout the submucosa. Interestingly, there are no glands in the oesophagus of rodents, while they occur in large numbers in the oesophagus of humans and pigs. The submucosa layer contains connective tissue cells, blood and lymphatic vessels, nerves, and glands. In humans and pig’s oesophagus, squamous cells are located in several layers, up to 10–15, and the cells are not keratinised. In the oesophagus of rodents, squamous cells are arranged to 4 to 5 layers and are typically keratinised. There are differences in the thickness and keratinization of the mucosa between species ( Figure 1). The mucosa layer is composed of squamous epithelial cells arranged in several rows. Epithelial cells are located in the mucosa and submucosa layers. The oesophagus consists of four layers, namely the mucosa, submucosa, muscularis externa, and adventitia. We believe that this review highlights important relationships which might contribute to a better understanding of the pathomechanisms of oesophageal diseases. This review summarizes our knowledge of the expression and function of oesophageal ion transporters and elucidates their role in oesophageal diseases. Disturbances of oesophageal ion transport might play a role in certain pathological conditions, such as eosinophilic oesophagitis (EoO), Barrett’s oesophagus (BO) and oesophageal cancer (OC). OE resistance involves a number of factors, such as ion transport processes through apical and basolateral membranes. OE resistance is an important defense mechanism which prevents cells from reflux-induced acidosis ( Fujiwara et al., 2005). Although the OE is not a typical secretory epithelium, its ion transport processes are of great importance with regard to epithelial resistance ( Orlando, 1986 Goldstein et al., 1994 Gunther et al., 2014). The oesophageal epithelium (OE) is built up from squamous epithelial cells (SECs) arranged in stratified layers. In contrast, the literature on ion transport in the oesophagus is limited. Therefore, a number of studies have been conducted to identify the presence and function of transport proteins on GI cells, especially in exocrine glands, the stomach and the colon ( Toth-Molnar et al., 2007 Venglovecz et al., 2008, 2011 Farkas et al., 2011 Hegyi et al., 2011 Czepan et al., 2012 Judak et al., 2014) both under physiological and pathophysiological conditions. Ion and water transport play a crucial role in the development of gastrointestinal (GI) diseases, such as cystic fibrosis or diarrhea. We believe that this review highlights important relationships which might contribute to a better understanding of the pathomechanisms of esophageal diseases. In this review, we discuss the physiological and pathophysiological roles of ion transporters in the oesophagus, highlighting transport proteins which serve as therapeutic targets or prognostic markers in eosinophilic oesophagitis, BO and esophageal cancer. A change in the function or expression of ion transporters has significance in the development or neoplastic progression of Barrett’s oesophagus (BO). In the oesophagus, ion transport proteins are part of the epithelial resistance, a mechanism which protects the oesophagus against reflux-induced damage. Ion transporters play an important role in several physiological functions, such as cell volume regulation, pH homeostasis and secretion. 4First Department of Medicine, University of Szeged, Szeged, Hungary.3Division of Gastroenterology, First Department of Medicine, Medical School, University of Pécs, Pécs, Hungary.
![ionic activation bypass ionic activation bypass](https://www.mdpi.com/computation/computation-06-00057/article_deploy/html/images/computation-06-00057-g003.png)
2Institute for Translational Medicine, Szentágothai Research Centre, Medical School, University of Pécs, Pécs, Hungary.1Department of Pharmacology and Pharmacotherapy, University of Szeged, Szeged, Hungary.Eszter Becskeházi 1†, Marietta Margaréta Korsós 1†, Bálint Erőss 2, Péter Hegyi 2,3,4 and Viktória Venglovecz 1*