Angiotensin II type I receptor modulates intracellular free Mg2+ in renally derived cells via Na+-dependent Ca2+-independent mechanisms.
Treatment of Madin-Darby canine kidney (MDCK) cells with the peptide hormone angiotensin II (Ang II) results in an increase in the concentrations of cytosolic free calcium ([Ca(2+)](i)) and sodium ([Na(+)](i)) with a concomitant decrease in cytosolic free Mg(2+) concentration ([Mg(2+)](i)). In the present study we demonstrate that this hormone-induced decrease in [Mg(2+)](i) is independent of [Ca(2+)](i) but dependent on extracellular Na(+). [Mg(2+)](i), [Ca(2+)](i), and [Na(+)](i) were measured in Ang II-stimulated MDCK cells by fluorescence digital imaging using the selective fluoroprobes mag-fura-2AM, fura-2AM, and sodium-binding benzofuran isophthalate (acetoxymethyl ester), respectively. Ang II decreased [Mg(2+)](i) and increased [Na(+)](i) in a dose-dependent manner. These effects were inhibited by irbesartan (selective AT(1) receptor blocker) but not by PD123319 (selective AT(2) receptor blocker). Imipramine and quinidine (putative inhibitors of the Na(+)/Mg(2+) exchanger) and removal of extracellular Na(+) abrogated Ang II-mediated [Mg(2+)](i) effects. In cells pretreated with thapsigargin (reticular Ca(2+)-ATPase inhibitor), Ang II-stimulated [Ca(2+)](i) transients were attenuated (p < 0.01), whereas agonist-induced [Mg(2+)](i) responses were unchanged. Clamping the [Ca(2+)](i) near 50 nmol/liter with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) inhibited Ang II-induced [Ca(2+)](i) increases but failed to alter Ang II-induced [Mg(2+)](i) responses. Benzamil, a selective blocker of the Na(+)/Ca(2+) exchanger, inhibited [Na(+)](i) but not [Mg(2+)](i) responses. Our data demonstrate that in MDCK cells, AT(1) receptors modulate [Mg(2+)](i) via a Na(+)-dependent Mg(2+) transporter that is not directly related to [Ca(2+)](i). These data support the notion that rapid modulation of [Mg(2+)](i) is not simply a result of Mg(2+) redistribution from intracellular buffering sites by Ca(2+) and provide evidence for the existence of a Na(+)-dependent, hormonally regulated transporter for Mg(2+) in renally derived cells.
Multidisciplinary Research Group on Hypertension, Clinical Research Institute of Montreal, University of Montreal, Montreal, Quebec H2W 1R7, Canada. touyzr@ircm.qc.ca
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D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001572:Benzofurans / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D016257:Fura-2 / Q000031:analogs & derivatives* / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007099:Imipramine / Q000494:pharmacology; D000077405:Irbesartan; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010455:Peptides / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011802:Quinidine / Q000494:pharmacology; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin / Q000502:physiology*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D013777:Tetrazoles / Q000494:pharmacology; D013997:Time Factors
D018759:Adrenergic Uptake Inhibitors; D000317:Adrenergic alpha-Antagonists; D000959:Antihypertensive Agents; D001572:Benzofurans; D001713:Biphenyl Compounds; D002120:Calcium Channel Agonists; D002614:Chelating Agents; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D007093:Imidazoles; D010455:Peptides; D011725:Pyridines; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; D013777:Tetrazoles; C013407:benzamil; C049925:fura-2-am; D000804:Angiotensin II; C061665:sodium-binding benzofuran isophthalate; C072323:Mag-Fura-2-acetoxymethyl ester; C073402:PD 123319; D004533:Egtazic Acid; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000584:Amiloride; D012964:Sodium; D008274:Magnesium; D011802:Quinidine; D000077405:Irbesartan; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D007099:Imipramine; D002118:Calcium; D016257:Fura-2