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J. Biol. Chem., Vol. 282, Issue 18, 13477-13486, May 4, 2007

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Real Time Measurements of Water Flow in Amphibian Gastric Glands

MODULATION VIA THE EXTRACELLULAR Ca²⁺-SENSING RECEPTOR^*

Andrea Gerbino¹, Gregorio Fistetto², Matilde Colella¹, Aldebaran M. Hofer³, Lucantonio Debellis¹, Rosa Caroppo¹, and Silvana Curci⁴

From the Dipartimento di Fisiologia Generale ed Ambientale, Universita' di Bari, 70126 Bari, Italy and the Veterans Affairs Boston Healthcare System and the Department of Surgery, Harvard Medical School and Brigham and Women's Hospital, West Roxbury, Massachusetts 02132

The mechanisms for the formation of the osmotic gradient driving water movements in the gastric gland and its modulation via the extracellular Ca²⁺-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.

Received for publication, November 14, 2006 , and in revised form, February 9, 2007.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Supported by Cofin, MURST, FIRB Grant RBIN04PHZ7 (Rome, I) and by Finanziamenti di Ateneo (Bari, I).

² Supported by a doctoral fellowship awarded jointly from the University of Bari and the European Community (FSE).

³ Supported by the Department of Veterans Affairs and the Brigham Surgical Group.

⁴ To whom correspondence should be addressed: Veterans Affairs Boston Healthcare System and the Dept. of Surgery, Harvard Medical School, Brigham and Women's Hospital, 1400 VFW Pkwy., West Roxbury, MA 02132. Tel.: 617-323-7700 (ext. 35902); Fax: 857-203-5592; E-mail: scurci{at}rics.bwh.harvard.edu.

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				A. M. Hofer and K. Lefkimmiatis Extracellular Calcium and cAMP: Second Messengers as "Third Messengers"? Physiology, October 1, 2007; 22(5): 320 - 327. [Abstract] [Full Text] [PDF]