Agonists for endothelial P2 purinoceptors trigger a signalling pathway producing Ca2+ responses in lymphocytes adherent to endothelial cells

P2U purinoceptors: cDNA cloning, signal transduction mechanisms and structure-function analysis

The cloning of a P2U purinoceptor cDNA has made it possible to use molecular biological approaches to investigate P2U purinoceptor function. Expression of recombinant P2U purinoceptors in mammalian cells lacking endogenous P2U purinoceptors has enabled us to characterize the receptor protein and its downstream effectors, and has allowed a partial analysis of the role of certain amino acid residues in ligand binding. These approaches have placed the pharmacological classification of the P2U purinoceptor on a firm molecular footing and have generated model systems that can be used to investigate receptor-ligand binding, regulation and signal transduction.

Sodium block and depolarization diminish P2Z-dependent Ca2+ entry in human B lymphocytes

Despite a high Ca2+ -permeability of the P2Z receptor in human B lymphocytes, extracellular ATP4- has only a minor effect on global [Ca2+]i. The aim of this study was to reveal the mechanisms responsible for this discrepancy. We investigated the relationship between ATP4- -application, Cai 2+ -response, membrane current and membrane potential in two human B cell lines and in human tonsillar B cells. This was achieved by a combination of FACS- and voltage clamp measurements and the usage of appropriate voltage- and Ca2 -sensitive fluorescent dyes. ATP4 -induced changes in whole-cell current and [Ca2]i were blocked by extracellular as well as intracellular Na+. Under current clamp conditions, ATP4- -induced Na+ -entry diminished the Ca2+ entry via reduction of the driving force. A substantial increase in [Ca2+]iinduced by ATP4- was only observed in Na+ -free solutions. The pathway of signal transduction activated by ATP4via P2Z receptor of human B lymphocytes under physiological conditions seems not to operate by an increase in the global intracellular Ca2+ -concentration, but rather by the depolarization of the cell membrane as a result of the Na+-influx.

Pharmacologic properties of P2Z/P2X7receptor characterized in murine dendritic cells: role on the induction of apoptosis

In the immune system, extracellular adenosine 5′-triphosphate (ATP) mediates a variety of effects mainly through activation of a particular receptor subtype, the pore-forming P2Z/P2X7 purinoceptor. This purinergic receptor has been described chiefly in cells of hemopoietic origin such as T cells, thymocytes, monocytes, macrophages, and phagocytic cells of thymic reticulum. In this study, we characterized the P2Z/P2X7 purinoceptor and the ATP-mediated apoptosis in murine spleen–derived dendritic cells (DCs). Dye uptake and apoptosis were evaluated by flow cytometry. ATP-treated DCs were permeable to different low-molecular-weight fluorescent probes such as ethidium bromide, YO-PRO 1, and lucifer yellow. Such an effect was dose-dependent (EC50: 721 μmol/L); mediated by the fully anionic agonist (ATP4−); and specifically stimulated by ATP, BzATP, and ATPγS. Additionally, an ATP-induced increase in intracellular calcium was detected by microfluorometry. Furthermore, ATP treatment induced a significant increase in apoptotic DCs (64.46% ± 3.8%) when compared with untreated control cells (34% ± 5.8%), as ascertained by the TdT-mediated dUTP nick end labeling technique. Both ATP-induced DC permeabilization and apoptosis were inhibited by oxidized ATP, a P2Z/P2X7-specific antagonist. In conclusion, we characterized the expression of the P2Z/P2X7purinoceptor in murine spleen–derived DCs and described its role on the induction of apoptosis.

Pharmacologic properties of P(2Z)/P2X(7 )receptor characterized in murine dendritic cells: role on the induction of apoptosis

In the immune system, extracellular adenosine 5'-triphosphate (ATP) mediates a variety of effects mainly through activation of a particular receptor subtype, the pore-forming P(2Z)/P2X(7) purinoceptor. This purinergic receptor has been described chiefly in cells of hemopoietic origin such as T cells, thymocytes, monocytes, macrophages, and phagocytic cells of thymic reticulum. In this study, we characterized the P(2Z)/P2X(7) purinoceptor and the ATP-mediated apoptosis in murine spleen-derived dendritic cells (DCs). Dye uptake and apoptosis were evaluated by flow cytometry. ATP-treated DCs were permeable to different low-molecular-weight fluorescent probes such as ethidium bromide, YO-PRO 1, and lucifer yellow. Such an effect was dose-dependent (EC(50): 721 micromol/L); mediated by the fully anionic agonist (ATP(4-)); and specifically stimulated by ATP, BzATP, and ATPgammaS. Additionally, an ATP-induced increase in intracellular calcium was detected by microfluorometry. Furthermore, ATP treatment induced a significant increase in apoptotic DCs (64. 46% +/- 3.8%) when compared with untreated control cells (34% +/- 5. 8%), as ascertained by the TdT-mediated dUTP nick end labeling technique. Both ATP-induced DC permeabilization and apoptosis were inhibited by oxidized ATP, a P(2Z)/P2X(7)-specific antagonist. In conclusion, we characterized the expression of the P(2Z)/P2X(7) purinoceptor in murine spleen-derived DCs and described its role on the induction of apoptosis.

Effects of UTP on membrane current and potential in rat aortic myocytes

The electrophysiological effects of UTP on freshly isolated rat aortic myocytes were examined using the perforated patch clamp technique. Application of alpha,beta-methylene ATP (alphabeta-meATP) and UTP, putative P2X and P2Y2 or P2Y4 purinoceptor agonists, induced transient and oscillatory inward currents, respectively. Experiments with Cl- channel blockers and different external Cl- concentrations demonstrated that the oscillatory current elicited by UTP is attributable to activation of Cl- channels. The transient component elicited by (alphabeta-meATP appeared to be responsible for a non-selective cationic current. With internal application of low-molecular-weight heparin, a blocker of inositol 1,4,5-trisphosphate (InsP3), the oscillatory current elicited by UTP was abolished. The oscillatory current was activated in an all-or-none manner by UTP over the concentration range 0.1 and 1 microM and the frequency and amplitude were independent of the UTP concentration. Under current-clamp mode, UTP produced an oscillatory membrane potential. These results show that rat aortic myocytes have at least two types of P2 receptors. Activation of the P2Y receptor by UTP produces InsP3, which releases Ca2+ from the store site. The resulting increase in intracellular Ca2+ concentration causes the oscillatory Cl- current and the subsequent membrane potential changes.