Bicarbonate secretion from the surface epithelial cells of the gastroduodenal mucosa is an active process depending upon the tissue metabolism and plays an important role as the first line of defense in mucosal protection in collaboration with the mucus gel. This secretion is regulated by humoral and neural factors as well as endogenous prostaglandins (PGs) and is considered to be intracellularly mediated by cyclic AMP in the duodenum and by cyclic GMP in the stomach. Ca2+ also acts as an intracellular mediator in this process. This bicarbonate secretion is markedly increased in response to luminal acid, mediated by PGs and neural factors including capsaicinsensitive sensory nerves, and the impairment of this response is involved in the pathogenesis of various duodenal ulcer models induced by cysteamine, nonsteroidal antiinflammatory drugs and stress. The mechanisms underlying the mucosal protection by HCO3- secretion is two fold; One is the direct neutralization of H+ in the lumen, and the other is the establishment of a pH gradient across the mucus gel aided by the physico-chemical property of the mucus. However, the cellular mechanisms of HCO3- secretion, including the receptors, the mediators and the signal transduction pathway have been poorly understood. The establishment of a method for preparing isolated epithelial cells and the probe for HCO3- secretion in isolated cells is required to further elucidate the mechanism of HCO3- secretion.
In recent years, reactive oxygen species have been implicated in the pathogenesis of a wide variety of disorders. Although the existence of reactive oxygen intermediates in drug metabolism can be inferred from end product analysis or from the effects of antioxidants or enzymes such as superoxide dismutase, only the technique of electron spin resonance (ESR) allows the direct detection of these highly reactive species. However, some free radical species cannot be detected by ESR due to their extremely short half-lives, which result in low steady-state concentrations of the radicals or to short radical relaxation times, which lead to a very broad line. These facts made recent development of spin-trapping and chemiluminescence techniques are widely used to detect free radicals. The goal of this paper is to introduce the various assays available for measurement of reactive oxygen species in biological models. This paper will focus on two topics : (1) the spin-trapping/ESR technique in vitro and vivo and (2) the chemiluminescence-optical biosensor application of this technique, a very sensitive method that has the advantage of being able to provide continuous, online, nondestructive monitoring of reactive oxygen species.