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Stimulation of secretion in permeabilized PC12 cells by adenosine 5'-[gamma-thio]triphosphate: possible involvement of nucleoside diphosphate kinase.

ABSTRACT: The addition of Ca2+, adenosine 5'-[gamma-thio]triphosphate (ATP[S]) or guanosine 5'-[gamma-thio]triphosphate (GTP[S]) to digitonin-permeabilized PC12 cells stimulates noradrenaline secretion. Both ATP[S] and GTP[S] stimulate release in the absence of Ca2+. Whereas ADP and adenosine 5'-[beta gamma-imido]triphosphate inhibited ATP[S]-stimulated release, they did not inhibit Ca(2+)-stimulated release even in the absence of added ATP. This suggests that the kinase which uses ATP[S] to induce secretion may not play an essential role in Ca(2+)-stimulated release. As GTP[S]-stimulated and ATP[S]-stimulated secretions were not additive, it seemed possible that stimulation by ATP[S] might in part result from the thiophosphorylation of GDP by nucleoside-diphosphate (NDP) kinase to form GTP[S]. The following results are consistent with this possibility. (1) A low concentration of GDP increased ATP[S]-stimulated secretion, but not GTP[S]-stimulated or Ca(2+)-stimulated secretion. (2) A variety of ribo- and deoxyribo-nucleoside di- and tri-phosphates inhibited ATP[S]-stimulated secretion, but not GTP[S]-stimulated or Ca(2+)-stimulated secretion. Thus, like NDP kinase, the kinase which uses ATP[S] to cause noradrenaline release appears to have a very low specificity for ATP. (3) Incubation of permeabilized cells in a sucrose-containing buffer resulted in the preferential loss of ATP[S]-stimulated secretion and a decrease in the level of NDP kinase. The addition of rat liver NDP kinase to those depleted cells partially restored ATP[S]-stimulated secretion.

SUBMITTER: Vu ND

PROVIDER: S-EPMC1137670 | biostudies-other | 1993 Nov

REPOSITORIES: biostudies-other

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Project description:Adenosine triphosphate (ATP) is released from cholangiocytes into bile and is a potent secretogogue by increasing intracellular Ca²(+) and stimulating fluid and electrolyte secretion via binding purinergic (P2) receptors on the apical membrane. Although morphological differences exist between small and large cholangiocytes (lining small and large bile ducts, respectively), the role of P2 signaling has not been previously evaluated along the intrahepatic biliary epithelium. The aim of these studies therefore was to characterize ATP release and P2-signaling pathways in small (MSC) and large (MLC) mouse cholangiocytes. The findings reveal that both MSCs and MLCs express P2 receptors, including P2X4 and P2Y2. Exposure to extracellular nucleotides (ATP, uridine triphosphate, or 2',3'-O-[4-benzoyl-benzoyl]-ATP) caused a rapid increase in intracellular Ca²(+) concentration and in transepithelial secretion (I(sc)) in both cell types, which was inhibited by the Cl(-) channel blockers 5-nitro-2-(-3-phenylpropylamino)-benzoic acid (NPPB) or niflumic acid. In response to mechanical stimulation (flow/shear or cell swelling secondary to hypotonic exposure), both MSCs and MLCs exhibited a significant increase in the rate of exocytosis, which was paralleled by an increase in ATP release. Mechanosensitive ATP release was two-fold greater in MSCs compared to MLCs. ATP release was significantly inhibited by disruption of vesicular trafficking by monensin in both cell types.These findings suggest the existence of a P2 signaling axis along intrahepatic biliary ducts with the "upstream" MSCs releasing ATP, which can serve as a paracrine signaling molecule to "downstream" MLCs stimulating Ca²(+)-dependent secretion. Additionally, in MSCs, which do not express the cystic fibrosis transmembrane conductance regulator, Ca²(+)-activated Cl(-) efflux in response to extracellular nucleotides represents the first secretory pathway clearly identified in these cholangiocytes derived from the small intrahepatic ducts.

Project description:Pseudomonas aeruginosa secretes copious amounts of an exopolysaccharide called alginate during infection in the lungs of cystic fibrosis patients. A mutation in the algR2 gene of mucoid P. aeruginosa is known to exhibit a nonmucoid (nonalginate-producing) phenotype and showed reduced activities of succinyl-coenzyme A (CoA) synthetase (Scs) and nucleoside diphosphate kinase (Ndk), implying coregulation of Ndk and Scs in alginate synthesis. We have cloned and characterized the sucCD operon encoding the alpha and beta subunits of Scs from P. aeruginosa and have studied the role of Scs in generating GTP, an important precursor in alginate synthesis. We demonstrate that, in the presence of GDP, Scs synthesizes GTP using ATP as the phosphodonor and, in the presence of ADP, Scs synthesizes ATP using GTP as a phosphodonor. In the presence of inorganic orthophosphate, succinyl-CoA, and an equimolar amount of ADP and GDP, Scs synthesizes essentially an equimolar amount of ATP and GTP. Such a mechanism of GTP synthesis can be an alternate source for the synthesis of alginate as well as for the synthesis of other macromolecules requiring GTP such as RNA and protein. Scs from P. aeruginosa is also shown to exhibit a broad NDP kinase activity. In the presence of inorganic orthophosphate (P(i)), succinyl-CoA, and either GDP, ADP, UDP or CDP, it synthesizes GTP, ATP, UTP, or CTP. Scs was previously shown to copurify with Ndk, presumably as a complex. In mucoid cells of P. aeruginosa, Ndk is also known to exist in two forms, a 16-kDa cytoplasmic form predominant in the log phase and a 12-kDa membrane-associated form predominant in the stationary phase. We have observed that the 16-kDa Ndk-Scs complex present in nonmucoid cells, synthesizes all three of the nucleoside triphosphates from a mixture of GDP, UDP, and CDP, whereas the 12-kDa Ndk-Scs complex specifically present in mucoid cell predominantly synthesizes GTP and UTP but not CTP. Such regulation may promote GTP synthesis in the stationary phase when the bulk of alginate is synthesized by mucoid P. aeruginosa.

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Stimulation of secretion in permeabilized PC12 cells by adenosine 5'-[gamma-thio]triphosphate: possible involvement of nucleoside diphosphate kinase.

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