Alkaline secretion by frog gastric glands measured with pH microelectrodes in the gland lumen

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Abstract
In the present work we have measured the pH of the secreted fluid within the gland lumen of isolated but intact gastric mucosa of Ranaesculenta. Tissues were mounted in a double chamber allowing continuous perfusion of the mucosal and serosal compartment, and the measurements were made with double‐barrelled pH glass microelectrodes inserted into the glands from the serosal surface under microscopic inspection. During inhibition of H+ secretion by cimetidine (100 μm) the luminal gland pH (pHgl) averaged 7.60 ± 0.05 pH units (mean ±s.e.m.; n= 35), a value significantly higher than bath solution pH (7.45 ± 0.02; P < 0.001) and also higher than intracellular pH of oxyntopeptic cells (pHi), which averaged 7.53 ± 0.06 (n= 18). Stimulation of acid secretion with histamine (500 μm) reversibly decreased pHgl to values which could be as low as 2.5. Together with electrophysiological criteria this response was routinely used to verify the proper location of the microelectrode tip within the gland lumen. Stimulation with carbachol (100 μm) or pentagastrin (50 μm) in the presence of cimetidine rapidly and reversibly increased pHgl by 0.10 ± 0.01 pH units (n= 24; P < 0.001) and 0.09 ± 0.02 pH units (n= 6; P < 0.05), respectively. The observation that gastric gland fluid is more alkaline than the bath solutions and that carbachol or pentagastrin further alkalinize it strongly suggests that oxyntopeptic cells participate in gastric alkaline secretion at least under cholinergic stimulation.