Gastric acid
The main constituent of gastric acid is hydrochloric acid which is produced by parietal cells (also called oxyntic cells) in the gastric glands in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the hydrochloric acid is secreted into the lumen of the stomach. The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, the acidity being maintained by the proton pump H/K ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide.
9-Hydroxyoctadecadienoic acid
9("S")-HODE and with progressively lesser potencies 9("S")-HpODE, a racemic mixture of 9-HODE, 13("S")-HpODE, and 13("S")-HODE directly activate human (but not mouse) GPR132 (i.e. G protein coupled receptor 132 or G2A) in Chinese hamster ovary cells made to express these receptors; 9("S")-HODE was also a more potent stimulator of human G2A than a series of mono-hydroxy arachidonic acid metabolites. GPR132 was initially described as a pH sensing receptor; the role(s) of 9-HODEs as well as other linoleic and arachidonic acid metabolites in activating GPR132 under the physiological and pathological conditions in which it is implicated to be involved(see (see GPR132 for a listing of these conditions) have not yet been determined. This determination, as it might apply to humans, is made difficult by the inability of these HODEs to activate rodent GPR132 and therefore to be analyzed in rodent models.