Purinergic P2X7 receptors mediate ATP-induced saliva secretion by the mouse submandibular gland.
ABSTRACT Salivary glands express multiple isoforms of P2X and P2Y nucleotide receptors, but their in vivo physiological roles are unclear. P2 receptor agonists induced salivation in an ex vivo submandibular gland preparation. The nucleotide selectivity sequence of the secretion response was BzATP > ATP > ADP > UTP, and removal of external Ca(2+) dramatically suppressed the initial ATP-induced fluid secretion ( approximately 85%). Together, these results suggested that P2X receptors are the major purinergic receptor subfamily involved in the fluid secretion process. Mice with targeted disruption of the P2X(7) gene were used to evaluate the role of the P2X(7) receptor in nucleotide-evoked fluid secretion. P2X(7) receptor protein and BzATP-activated inward cation currents were absent, and importantly, purinergic receptor agonist-stimulated salivation was suppressed by more than 70% in submandibular glands from P2X(7)-null mice. Consistent with these observations, the ATP-induced increases in [Ca(2+)](i) were nearly abolished in P2X(7)(-/-) submandibular acinar and duct cells. ATP appeared to also act through the P2X(7) receptor to inhibit muscarinic-induced fluid secretion. These results demonstrate that the ATP-sensitive P2X(7) receptor regulates fluid secretion in the mouse submandibular gland.
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ABSTRACT: P2Y receptors are widely expressed in all gastrointestinal (GI) epithelia. Commonly, one epithelial tissue or cell expresses several P2Y receptors, which are located in both the apical and basolateral membranes. In almost all studied GI tissues, stimulation of P2Y receptors activates ion secretion, either that of NaCl, KCl, NaHCO3, or KHCO3. In most GI epithelia, an apical P2Y2 receptor is responsible for these ion secretory effects. Major progress during the last 10 years now permits integrated concepts of purinergic regulation of epithelial function. Most importantly, the apical mucus layer can be viewed as a restricted space for local paracrine purinergic regulation of ion transport. Extracellular ATP is present in the mucus in sufficiently high concentrations to activate apical P2Y receptors. Several physiological stimuli have been identified or suggested to trigger ATP release into the luminal space. These include flow-induced, primary cilium-dependent ATP secretion into the bile, acidic intraluminal pH in the duodenum, and agonist-activated secretion of ATP by secretory salivary and pancreatic acini as well as the intestinal crypts. A functional role of the intestinal alkaline phosphatase as ATP cleavage enzyme and thus signal termination is another novel discovery important for duodenal secretion. The overall functional consequence of apical P2Y receptor function is to provide an additional input signal to activate digestive fluid secretion when demanded for by a given physiological stimulus. WIREs Membr Transp Signal 2013, 2:27–36. doi: 10.1002/wmts.74 For further resources related to this article, please visit the WIREs website.Wiley Interdisciplinary Reviews: Membrane Transport and Signaling. 01/2013; 2(1).
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ABSTRACT: The P2X7 receptor (P2X7R) is a ligand-gated ion channel that conducts Na(+), K(+), and Ca(2+) when activated by extracellular ATP. In various cell types, such as secretory epithelia, the P2X7R is co-expressed with Ca(2+)-dependent Cl(-) channels of the TMEM16/anoctamin family. Here, we studied whether the P2X7R and TMEM16A/anoctamin-1 (Ano1) or TMEM16F/anoctamin-6 (Ano6) interact functionally and physically, using oocytes of Xenopus laevis and Ambystoma mexicanum (Axolotl) for heterologous expression. As a control, we co-expressed anoctamin-1 with the P2Y1 receptor (P2Y1R), which induces the release of Ca(2+) from intracellular stores via activating phospholipase C through coupling to Gαq. We found that co-expression of anoctamin-1 with the P2Y1R resulted in a small transient increase in Cl(-) conductance in response to ATP. Co-expression of anoctamin-1 with the P2X7R resulted in a large sustained increase in Cl(-) conductance via Ca(2+) influx through the ATP-opened P2X7R in Xenopus and in Axolotl oocytes, which lack endogenous Ca(2+)-dependent Cl(-) channels. P2Y1R- or P2X7R-mediated stimulation of Ano1 was primarily functional, as demonstrated by the absence of a physically stable interaction between Ano1 and the P2X7R. In the pancreatic cell line AsPC-1, we found the same functional Ca(2+)-dependent interaction of P2X7R and Ano1. The P2X7R-mediated sustained activation of Ano1 may be physiologically relevant to the time course of stimulus-secretion coupling in secretory epithelia. No such increase in Cl(-) conductance could be elicited by activating the P2X7 receptor in either Xenopus oocytes or Axolotl oocytes co-expressing Ano6. The lack of function of Ano6 can, at least in part, be explained by its poor cell-surface expression, resulting from a relatively inefficient exit of the homodimeric Ano6 from the endoplasmic reticulum.Pflugers Archiv : European journal of physiology. 01/2015;
- Journal of Oral and Maxillofacial Surgery, Medicine, and Pathology. 07/2014; 26(3):379-389.