TRANSITIONS AND TRANSPORT IN GASTRIC MUCOSA

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The general goals of this work are to understand the membrane mechanisms involved in C1 secretion by oxyntic cells and surface cells of the gastric mucosa as well as the different cellular processes which serve to regulate this transport. The first aim is to investigate whether membrane Na-H and C1-HCO3 exchangers may be contributing to this transport. A cytoplasmic-trapped, fluorescent dye (so-called BCECF) will be used to monitor quantitatively the cellular pH (pHc) in isolated gastric glands and in isolated purified oxynthic cells and surface cells from rabbit stomach. Measurements of Phc during a variety of experimental treatments (altered solution concentrations of Na, C1 and HCO3/CO2; use of specific inhibitors like amiloride for Na-H exchange and SITS for C1-HCO3 exchange) will allow us to determine whether such exchangers are operational in gastric mucosa. These data will also provide unique information regarding the ability of gastric cells to regulate their pHc. Further information about the C1-HCO3 exchnager will be obtained by monitoring the flux of the fluorescent dye NBD-taurine, which moves across red cell membranes only through the exchanger. The second goal is to measure rapid, unidirectional uptakes of 22 Na, 36 C1 and 42K (or 86 Rb) in isolated rabbit surface cells and oxynthic cells to determine whether these cells contain other mechanisms (e.g. NaC1 or NaKC12) besides the exchangers for accumulating C1. The final goal is to determine some of the mechanisms by which the oxynthic cells and surface cells regulate the activity of these membrane exchangers and co-transporters. Since [Ca]c has been implicated as a cellular second messenger for many cell types (including the stomach), we will utilize the cytoplasmic-trapped fluroescent, Ca-sensitive dye (so-called Quin 2) for quantitatively measuring [Ca]c during conditions in which C1 transport and the activity of the cells has been altered. Interactions among [Ca]c, pHc and other cellular second messengers (e.g. eyclic nucleotides, C-kinase) will also be investigated. These experiments will yield information about how gastric cells generate and control C1 secretion. Since there are many direct relationships among H, C1 and OH/HCO3 transport by gastric cells, this work will have implications about the ability of: (1) the oxyntic cells to secrete HC1; (ii) the surface cells to secrete OH/HCO3 and thereby maintain the so-called mucus/HCO3 barrier; (iii) both cell types to regulate their cytoplasmic pH in the face of the highly acidic stomach contents.