Direct pH microelectrode measurement of acid and alkaline secretion in glands of frog gastric mucosa

Gastric gland secretory properties have been studied by a new approach that allows the gland lumen pH (pHgl) to be measured with double-barrelled microelectrodes in isolated intact gastric mucosa perfused in vitro. After puncturing an oxyntic cell (OC) from the serosal surface, the microelectrode tip was advanced towards the gland lumen until the electrical recordings became equal to transepithelially measured potential (Vt) and resistance (Rt) values. In 15 resting mucosae (0.1 mM cimetidine) perfused on either surface with HCO3 Ringer solution, Vt and Rt were -20.7 SE ± 2.3 mV and 428 ± 52 Ω·cm2, respectively; pHgl was 7.68 ± 0.09, a value significantly higher (p<0.05) than solution (pH 7.48). Perfusion of the lumen with HCO3-free buffer solutions (pH between 6.4 and 8.4) produced corresponding changes of pHgl indicating that the luminal perfusate has relatively fast access to the gland lumen (90% of the maximum value was reached within 5 min). Following stimulation with histamine (0.5 mM) pHgl became progressively acidic and reached values between 5.3 and 2.2 within 30 min (n=8). On the other hand, stimulation with carbachol (0.1 mM) in presence of cimetidine. significantly alkalinized the gland lumen by 0.11 ± 0.02 pH units (n=11; p<0.001). The latter data support our recent findings that OC are able to secrete bicarbonate under carbachol stimulation. The fact that in resting state pHgl is higher than the pH of Ringer solution suggests that OC participate also to basal alkaline secretion.