Esophageal pH monitoring developed a dependable external reference electrode. Using this technique to monitor esophageal acid exposure patients for periods up to 24 hours, DeMeester and Johnson were able to identify the most important parameters of esophageal acid exposure, and they developed a composite pH score to quantify gastroesophageal reflux. The initial 24-hour pH studies required hospitalization until the introduction of microcircuits in the 1980s that allowed portable esophageal pH monitoring in an outpatient setting. Gastroesophageal reflux disease (GERD) is a common disease in western countries. In the United States, 7% of the population experiences heartburn daily and 44% at least once a
6TMS neutral amino acid transporter family the Transporter Classification Database. A gene encoding a small neutral amino acid transporter was cloned from the genome of the hyperthermophilic archaeon "Thermococcus" sp. KS-1. The cloned gene, "snatA", encodes a protein of 216 amino acid residues, SnatA (TC# 2.A.95.1.4), with six membrane-spanning segments (TMSs). Competition studies indicated that SnatA transports various L-type neutral amino acids. It has also been noted that glycine transport is inhibited by a protonophore, FCCP, or valinomycin plus nigericin, indicating that the process is dependent on an electrochemical potential of H. The generalized reaction catalyzed by SnatA is:Amino acid (in) → Amino acid (out) MarC