Real time measurements of water flow in amphibian gastric glands: modulation via the extracellular Ca2+-sensing receptor.

Andrea Gerbino, Gregorio Fistetto, Matilde Colella, Aldebaran M Hofer, Lucantonio Debellis, Rosa Caroppo, Silvana Curci

Index: J. Biol. Chem. 282(18) , 13477-86, (2007)

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Abstract

The mechanisms for the formation of the osmotic gradient driving water movements in the gastric gland and its modulation via the extracellular Ca(2+)-sensing receptor (CaR) were investigated. Real time measurements of net water flux in the lumen of single gastric glands of the intact amphibian stomach were performed using ion-selective double-barreled microelectrodes. Water movement was measured by recording changes in the concentration of impermeant TEA(+) ions ([TEA(+)](gl)) with TEA(+)-sensitive microelectrodes inserted in the lumen of individual gastric glands. Glandular K(+) (K(+)(gl)) and H(+) (pH(gl)) were also measured by using K(+)- and H(+)-sensitive microelectrodes, respectively. Stimulation with histamine significantly decreased [TEA](gl), indicating net water flow toward the gland lumen. This response was inhibited by the H(+)/K(+)-ATPase inhibitor, SCH 28080. Histamine also elicited a significant and reversible increase in [K(+)](gl) that was blocked by chromanol 293B, a blocker of KCQN1 K(+) channels. Histamine failed to induce net water flow in the presence of chromanol 293B. In the "resting state," stimulation of CaR with diverse agonists resulted in significant increase in [TEA](gl). CaR activation also significantly reduced histamine-induced water secretion and apical K(+) transport. Our data validate the strong link between histamine-stimulated acid secretion and water transport. We also show that cAMP-dependent [K(+)](gl) elevation prior to the onset of acid secretion generates the osmotic gradient initially driving water into the gastric glands and that CaR activation inhibits this process, probably through reduction of intracellular cAMP levels.