title: Adenosine modulates Mg(2+) uptake in distal convoluted tubule cells via A(1) and A(2) purinoceptors.
abstract: tk;1Adenosine plays a role in the control of water and electrolyte reabsorption in the distal tubule. As the distal convoluted tubule is important in the regulation of renal Mg(2+) balance, we determined the effects of adenosine on cellular Mg(2+) uptake in this segment. The effect of adenosine was studied on immortalized mouse distal convoluted tubule (MDCT) cells, a model of the intact distal convoluted tubule. The rate of Mg(2+) uptake was measured with fluorescence techniques using mag-fura 2. To assess Mg(2+) uptake, MDCT cells were first Mg(2+) depleted to 0.22 +/- 0.01 mM by being cultured in Mg(2+)-free media for 16 h and then placed in 1.5 mM MgCl(2); next, changes in intracellular Mg(2+) concentration ([Mg(2+)](i)) were determined. [Mg(2+)](i) returned to basal levels, 0.53 +/- 0.02 mM, with a mean refill rate, d([Mg(2+)](i))/dt, of 137 +/- 16 nM/s. Adenosine stimulates basal Mg(2+) uptake by 41 +/- 10%. The selective A(1) purinoceptor agonist N(6)-cyclopentyladenosine (CPA) increased intracellular Ca(2+) and decreased parathyroid hormone (PTH)-stimulated cAMP formation and PTH-mediated Mg(2+) uptake. On the other hand, the selective A(2) receptor agonist 2-[p-(2-carbonyl-ethyl)-phenylethylamino]-5'-N-ethylcarboxamidoadenosine (CGS) stimulated Mg(2+) entry in a concentration-dependent fashion. CGS increased cAMP formation and the protein kinase A inhibitor RpcAMPS inhibited CGS-stimulated Mg(2+) uptake. Selective inhibition of phospholipase C, protein kinase C, or mitogen-activated protein kinase enzyme cascades with U-73122, Ro-31-8220, and PD-98059, respectively, diminished A(2) agonist-mediated Mg(2+) entry. Aldosterone potentiated CGS-mediated Mg(2+) entry, and elevation of extracellular Ca(2+) diminished CGS-responsive cAMP formation and Mg(2+) uptake. Accordingly, MDCT cells possess both A(1) and A(2) purinoceptor subtypes with intracellular signaling typical of these respective receptors. We conclude that adenosine has dual effects on Mg(2+) uptake in MDCT cells through separate A(1) and A(2) purinoceptor pathways.
authors.affiliation: Department of Medicine, University of British Columbia, Vancouver Hospital and Health Sciences Centre, Vancouver, British Columbia, Canada V6T 1Z3.
authors.forename: H S
authors.initials: HS
authors.lastname: Kang
authors.forename: D
authors.initials: D
authors.lastname: Kerstan
authors.forename: L J
authors.initials: LJ
authors.lastname: Dai
authors.forename: G
authors.initials: G
authors.lastname: Ritchie
authors.forename: G A
authors.initials: GA
authors.lastname: Quamme
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002461:Cell Line, Transformed; D000242:Cyclic AMP / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D007686:Kidney Tubules, Distal / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D051379:Mice; D010281:Parathyroid Hormone / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1 / Q000502:physiology*; D013805:Theobromine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D010281:Parathyroid Hormone; D010627:Phenethylamines; D047428:Protein Kinase Inhibitors; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D014970:Xanthines; C061281:2-phenethylamino-5'-N-ethylcarboxamidoadenosine; C048599:N(6)-cyclopentyladenosine; D000450:Aldosterone; C057837:3,7-dimethyl-1-propargylxanthine; D000255:Adenosine Triphosphate; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000242:Cyclic AMP; D008274:Magnesium; D000241:Adenosine; D013805:Theobromine; D002118:Calcium