Effects of increased O2 and CO2 on acid secretion by dogfish gastric mucosa in vitro.

The gastric mucosa of the dogfish (Squalus acanthias), as usually prepared for in vitro chambered experiments, shows a secretory rate (JH) of about 2 mueq/cm2-h, but a potential difference (PD) of zero. Raising PCO2 from 0.05 to 0.1 atm increases JH by 40% and causes the development of a PD of about 2 mV, mucosal surface positive. Increasing PO2 from 0.9 to 1.9 atm in a hyperbaric chamber (at constant PCO2 = 0.1 atm) doubles JH and increases PD to 5 mV. Transepithelial resistance falls by 20% at high PO2. It appears that the dogfish gastric mucosa, like that of the frog, is rate limited by CO2 diffusion into the tissue from the usual 5% mixture and is also rate limited by the usual O2 levels (unlike the frog), presumably due to its thicker structure and higher O2 consumption. The mucosal-positive PD, which is reversed from all other mucosae studied, is readily explained by separate electrogenic H+ and Cl- pumps, but less readily by schemes embodying a neutral HCl pump. It is not yet known whether the hyperbaric conditions are sufficient to ensure O2 sufficiency.