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Direct measurement of acid permeation into rat oesophagus

¹ West Los Angeles Veterans Affairs Medical Centre, CURE: Digestive Diseases Research Centre, and Department of Medicine, School of Medicine, University of California Los Angeles, Los Angeles, CA, 90073, USA
² Department of Physiology, Indiana University, School of Medicine, Indianapolis, Indiana, 46202, USA

Correspondence to:
Correspondence to:
Dr J D Kaunitz, West Los Angeles VA Medical Centre, Bldg 114, Room 217, 11301 Wilshire Blvd, Los Angeles, CA 90073, USA;
jake{at}ucla.edu

ABSTRACT
Background and aims: The early responses of the oesophageal mucosa to acid perfusion may predict subsequent pathology. Mucosal responses to luminal acid may result either from acid permeating through the mucosa or from other unknown transduction mechanisms. In order to better understand the dynamics of acid permeation into the oesophageal mucosa, we measured interstitial pH (pH_int) of the oesophageal basal epithelial layer, pre-epithelial layer thickness, and blood flow in rats in vivo during luminal acid challenge. A novel confocal microscopic technique was used in vitro to measure pH_int from defined cellular sites in response to luminal and basolateral acidification.

Methods: 5-(and-6)-Carboxyfluorescein (CF) and carboxy-seminapthorhodofluor-1 (SNARF-1) fluorescence was used to measure pH_int by conventional and confocal microscopy, respectively, in urethane anaesthetised rats. Pre-epithelial layer thickness was measured optically with carbon particles as markers. Blood flow was measured with laser Doppler flowmetry.

Results: Luminal acidification failed to alter pH_int in vivo and in vitro, but pH_int was lowered by modest serosal acidification. Pre-epithelial layer thickness and blood flow increased significantly during luminal surface acid perfusion. Indomethacin had no effect on any acid related response.

Conclusion: In this first dynamic measurement of oesophageal acid permeation and pre-epithelial layer thickness, pH_int was preserved in spite of high luminal acidity by two complementary techniques. Despite the apparent permeability barrier to acid permeation, oesophageal blood flow and thickness responded to luminal acid perfusion.

Keywords: carboxyfluorescein; confocal microscopy; blood flow; pre-epithelial layer thickness; microscopy

Abbreviations: pH_int, interstitial pH; pH_i, intracellular pH; CF, 5-(and-6)-carboxy fluorescein; SNARF-1, carboxy-seminap-thorhodofluor-1; FI, fluorescent intensity; BGI, background intensity

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