Interleukin (IL)-17-producing CD4(+) T lymphocytes (T(H)17 cells) constitute a subset of T-helper cells involved in host defence and several immune disorders. An intriguing feature of T(H)17 cells is their selective and constitutive presence in the intestinal lamina propria. Here we show that adenosine 5'-triphosphate (ATP) that can be derived from commensal bacteria activates a unique subset of lamina propria cells, CD70(high)CD11c(low) cells, leading to the differentiation of T(H)17 cells. Germ-free mice exhibit much lower concentrations of luminal ATP, accompanied by fewer lamina propria T(H)17 cells, compared to specific-pathogen-free mice. Systemic or rectal administration of ATP into these germ-free mice results in a marked increase in the number of lamina propria T(H)17 cells. A CD70(high)CD11c(low) subset of the lamina propria cells expresses T(H)17-prone molecules, such as IL-6, IL-23p19 and transforming-growth-factor-beta-activating integrin-alphaV and -beta8, in response to ATP stimulation, and preferentially induces T(H)17 differentiation of co-cultured naive CD4(+) T cells. The critical role of ATP is further underscored by the observation that administration of ATP exacerbates a T-cell-mediated colitis model with enhanced T(H)17 differentiation. These observations highlight the importance of commensal bacteria and ATP for T(H)17 differentiation in health and disease, and offer an explanation of why T(H)17 cells specifically present in the intestinal lamina propria.

Extracellular ATP exerts its effects through P2 purinoceptors: these are ligand-gated ion channels (P2x) or G-protein-coupled receptors (P2Y, P2U). ATP at P2x receptors mediates synaptic transmission between neurons and from neurons to smooth muscle, being responsible, for example, for sympathetic vasoconstriction in small arteries and arterioles. We have now cloned a complementary DNA encoding the P2x receptor from rat vas deferens and expressed it in Xenopus oocytes and mammalian cells. ATP activates a cation-selective ion channel with relatively high calcium permeability. Structural predictions suggest that the protein (399 amino acids long) is mostly extracellular and contains only two transmembrane domains plus a pore-forming motif which resembles that of potassium channels. The P2x receptor thus defines a new family of ligand-gated ion channels.

P2X1 receptors for ATP are ligand-gated cation channels, present on many excitable cells including vas deferens smooth muscle cells. A substantial component of the contractile response of the vas deferens to sympathetic nerve stimulation, which propels sperm into the ejaculate, is mediated through P2X receptors. Here we show that male fertility is reduced by approximately 90% in mice with a targeted deletion of the P2X1 receptor gene. Male mice copulate normally--reduced fertility results from a reduction of sperm in the ejaculate and not from sperm dysfunction. Female mice and heterozygote mice are unaffected. In P2X1-receptor-deficient mice, contraction of the vas deferens to sympathetic nerve stimulation is reduced by up to 60% and responses to P2X receptor agonists are abolished. These results show that P2X1 receptors are essential for normal male reproductive function and suggest that the development of selective P2X1 receptor antagonists may provide an effective non-hormonal male contraceptive pill. Also, agents that potentiate the actions of ATP at P2X1 receptors may be useful in the treatment of male infertility.

P2X receptors for ATP are a family of ligand-gated cation channels. There are 11 conserved positive charges in the extracellular loop of P2X receptors. We have generated point mutants of these conserved residues (either Lys 3 Arg, Lys 3 Ala, Arg 3 Lys, or Arg 3 Ala) in the human P2X 1 receptor to determine their contribution to the binding of negatively charged ATP. ATP evoked concentration-dependent (EC 50 ϳ 0.8 M) desensitizing responses at wild-type (WT) P2X 1 receptors expressed in Xenopus oocytes. Suramin produced a parallel rightward shift in the concentration response curve with an estimated pK B of 6.7. Substitution of amino acids at positions Lys-53, Lys-190, Lys-215, Lys-325, Arg-202, Arg-305, and Arg-314 either had no effect or only a small change in ATP potency, time course, and/or suramin sensitivity. Modest changes in ATP potency were observed for mutants at K70R and R292K/A (20-and 100-fold decrease, respectively). Mutations at residues K68A and K309A reduced the potency of ATP by >1400-fold and prolonged the time course of the P2X 1 receptor current but had no effect on suramin antagonism. Lys-68, Lys-70, Arg-292, and Lys-309 are close to the predicted transmembrane domains of the receptor and suggest that the ATP binding pocket may form close to the channel vestibule.P2X receptors for ATP are ligand-gated cation channels present on many different cell types including neurons, blood cells, and smooth muscle (1). The P2X 1 receptor was originally cloned from the rat vas deferens, and its properties, in particular the rapid desensitization and sensitivity to ␣,␤-meATP, correspond closely to those of the native smooth muscle phenotype (2). This has been confirmed in recent studies on P2X 1 receptor-deficient mice that showed the P2X 1 receptor is essential for the expression of functional P2X receptors in smooth muscle (3).Seven P2X receptors (P2X 1-7 ) have been identified at the molecular level (4), and they constitute a novel family of ion channels with two transmembrane domains, intracellular amino and carboxyl termini and a large extracellular loop (5). The receptors form as either homo-or heteromultimers (6, 7) from the association of at least three P2X receptor subunits (8). The second transmembrane domain lines the ion conducting pore (9), and residues on the amino and carboxyl termini are involved in determining the time course of the response of P2X 2 receptors (10 -13). The extracellular loop is thought to be the site of ATP binding, and residues that affect antagonist action have been described (14,15). A Walker ATP binding motif (16) is not present in P2X receptors, and to date no residues associated with agonist binding have been identified.In many ATP-binding proteins, positively charged amino acids have been shown to be important in co-ordinating ATP binding. One of the key components of the Walker motif is the lysine residue, which is thought to interact directly with one of the phosphate groups of the ATP molecule (17) (for a review, see Ref. 18). Lysine residues are also important...

In addition to its diverse functions inside cells, ATP can act at several types of cell-surface receptor. One of these (P2X-purinoceptor) is believed to be a ligand-gated cation channel. The presence of P2X receptors on autonomic, sensory and central neurons suggests that ATP might be released to act as a fast excitatory synaptic transmitter. Here we record excitatory synaptic potentials and currents from cultured coeliac ganglion neurons which are mimicked by ATP, blocked by the P2-purinoceptor antagonist suramin, desensitized by alpha,beta-methylene-ATP and unaffected by antagonists acting at nicotine, 5-hydroxytryptamine, N-methyl-D-aspartate (NMDA), non-NMDA glutamate, gamma-aminobutyric acid (GABA), noradrenaline or adenosine receptors. We conclude that ATP is the neurotransmitter at this neuroneuronal synapse.