Functional characterization and expression of PBR in rat gastric mucosa: stimulation of chloride secretion by PBR ligands

Abstract

Previous studies have demonstrated that gastric mucosa contained high levels of the polypeptide diazepam binding inhibitor, the endogenous ligand of the peripheral-type benzodiazepine receptor (PBR). However, the expression and function of this receptor protein in these tissues have not been investigated. Immunohistochemistry identified an intense PBR immunoreactivity in the mucous and parietal cells of rat gastric fundus and in the mucous cells of antrum. Immunoelectron microscopy revealed the mitochondrial localization of PBR in these cells. Binding of isoquinoline PK 11195 and benzodiazepine Ro5-4864 to gastric membranes showed that fundus had more PBR-binding sites than antrum, displaying higher affinity for PK 11195 than Ro5-4864. In a Ussing chamber, PK 11195 and Ro5-4864 increased short-circuit current (I(sc)) in fundic and antral mucosa in a concentration-dependent manner in the presence of GABA(A) and central benzodiazepine receptor (CBR) blockers. This increase in I(sc) was abolished after external Cl(-) substitution and was sensitive to chloride channels or transporter inhibitors. PK 11195-induced chloride secretion was also 1) sensitive to verapamil and extracellular calcium depletion, 2) blocked by thapsigargin and intracellular calcium depletion, and 3) abolished by the mitochondrial pore transition complex inhibitor cyclosporine A. PK 11195 had no direct effect on H(+) secretion, indicating that it stimulates a component of Cl(-) secretion independent of acid secretion in fundic mucosa. These data demonstrate that mucous and parietal cells of the gastric mucosa express mitochondrial PBR functionally coupled to Ca(2+)-dependent Cl(-) secretion, possibly involved in the gastric mucosa protection.

Role of Na-K-2Cl cotransporter-1 in gastric secretion of nonacidic fluid and pepsinogen

“…8). There is some evidence that it may be subject to regulation by other signals: in the rat gastric corpus, for example, peripheral-type benzodiazepine receptor agonists have been found to stimulate bumetanide-sensitive electrogenic Cl Ϫ secretion without influencing acid secretion (56). This mitochondrial receptor is expressed only in surface epithelial cells and basilar parietal cells of the rat stomach (56); the coexistence of this receptor and NKCC only in basilar parietal cells supports the notion that bumetanide-sensitive electrogenic Cl Ϫ secretion originates from this subset of parietal cells.…”

Translocator protein (18 kDa) is involved in primitive erythropoiesis in zebrafish

“…Protein levels were quantified using the dye-binding Bio-Rad assay with BSA as standard. Binding of [ 3 H]PK 11195 (specific activity 83.5 Ci/mmol) to membrane fractions was performed as described previously (32). In brief, 1-2 g of membrane fractions were incubated at 25°C in the presence of 33 nM [ 3 H]PK 11195 with or without a 1000-fold more concentrated cold PK 11195 solution.…”

Function of GABAergic and glutamatergic neurons in the stomach

“…Class one GABA A receptor is a ligand-gated chloride channel specifically blocked by bicuculline and picrotoxin, heterooligomers composed of the a, b, c, d, and e subunit families. The distribution of GABA A receptor subunit mRNAs in adult rat ENS is heterogenous [5,18,19], reflecting a varied physiological/pharmacological profile of GABA-mediated transmission in both regions. The expression of the presence of GABA A receptor subunit (a, b, c) mRNAs by in situ hybridization in myenteric and submucosal neurons [20], generally two pairs of a and b subunits and a c subunit in the gut.…”