Region-specific distribution of the P2Y 4 receptor in enteric glial cells and interstitial cells of Cajal within the guinea-pig gastrointestinal tract Luc Van Nassauw a , Anna Costagliola b , Joeri Van Op den Bosch a , Aldo Cecio b , Jean-Marie Vanderwinden c , Geoffrey Burnstock d , Jean-Pierre Timmermans a, * a Laboratory of Cell Biology and Histology, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium b Department Biological Structures, Functions and Technology, University of Naples Federico II, Italy c Laboratory of Neurophysiology, Universite ´ Libre de Bruxelles, Belgium d Autonomic Neuroscience Institute, Royal Free and University College Medical School-London, UK Received 15 November 2005; received in revised form 16 February 2006; accepted 27 February 2006 Abstract Although there is pharmacological evidence to assume that the P2Y 4 receptor is a regulator of epithelial ion transport, no detailed data about its distribution within the gut are available. Therefore, this study, using whole mounts and cryosections, aimed to reveal the expression pattern of P2Y 4 along the entire guinea-pig gastrointestinal tract. P2Y 4 immunoreactivity was absent from enteric neurons but present in enteric glial cells of the stomach, small and large intestine. In the esophagus, P2Y 4 appeared to be exclusively located within striated muscle cells. P2Y 4 showed also a region dependency regarding its presence in different subpopulations of interstitial cells of Cajal: in myenteric interstitial cells of Cajal in the stomach and ileum; in some intramuscular interstitial cells in the stomach and cecum; in some deep muscular plexus interstitial cells in the ileum; and in some submucosal surface interstitial cells in the colon. These results and the knowledge that P2Y 4 activation causes intracellular Ca 2+ recruitment led us to suggest that P2Y 4 in enteric glia plays a modulatory role in intercellular Ca 2+ waves, while P2Y 4 in interstitial cells of Cajal modulates intracellular Ca 2+ oscillations. D 2006 Elsevier B.V. All rights reserved. Keywords: P2Y 4 receptor; Gastrointestinal tract; Interstitial cell of Cajal; Enteric glia 1. Introduction Adenine and uridine nucleotides are present in all types of cells and are released in response to various stimuli. Once in the extracellular space, they are able to activate membrane proteins, which are categorized as P2 receptors, comprising ionotropic P2X and metabotropic P2Y recep- tors. P2Y receptors are characterized by seven putative transmembrane domains typical of G protein-coupled receptors. At present, 15 heptahelical proteins have been associated with the P2Y receptor family. However, only eight P2Y receptors (P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 , P2Y 11 , P2Y 12 , P2Y 13 and P2Y 14 ) are accepted as clearly defined, distinct, nucleotide receptors. P2Y receptors can be broadly subdivided into G q -coupled subtypes (P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 and P2Y 11 ) and G i -coupled subtypes (P2Y 12 , P2Y 13 and P2Y 14 ) (for review, see King and Burnstock, 2002; Burnstock and Knight, 2004). The P2Y 4 receptor was cloned first from human placenta (Communi et al., 1995) and from genomic human DNA (Nguyen et al., 1995), followed by cloning of rat (Bogdanov et al., 1998; Webb et al., 1998) and mouse (Lazarowski et al., 2001; Suarez-Huerta et al., 2001) orthologs. The human P2Y 4 receptor is a selective UTP receptor, whereas the rodent ones are equipotently activated by UTP and ATP. P2Y 4 mRNA has been detected in the murine stomach and intestine (Suarez-Huerta et al., 2001; Robaye et al., 2003), in murine colonic crypts (Matos et al., 2005), and in rat (Christofi et al., 2004) and guinea-pig (Cooke et al., 2004) colonic submucosa. Pharmacological studies have provided evidence that the P2Y 4 receptor is a dominant nucleotide- 1566-0702/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.autneu.2006.02.018 * Corresponding author. Tel.: +32 3 2653300; fax: +32 3 2653301. E-mail address: jean-pierre.timmermans@ua.ac.be (J.-P. Timmermans). Autonomic Neuroscience: Basic and Clinical 126 – 127 (2006) 299 – 306 www.elsevier.com/locate/autneu