title: Sodium-dependent recovery of ionised magnesium concentration following magnesium load in rat heart myocytes.
abstract: Our objectives were to investigate regulation of intracellular ionised Mg2+ concentration ([fMg2+]i) in cardiac muscle and cardiac Na+/Mg2+ antiport stoichiometry. [fMg2+]i was measured at 37 degrees C in isolated rat ventricular myocytes with mag-fura-2. Superfusion of myocytes with Na+ and Ca2+ free solutions containing 30 mM Mg2+ for 15 min more than doubled [fMg2+]i from its basal level (0.75 mM). Re-addition of Na+ caused [fMg2+]i to fall exponentially with time to basal level, the rate increasing linearly with [Na+]. Log(recovery rate) increased linearly with log([Na+]), the slope of 1.06 (95% confidence limits, 0.94-1.17) suggesting one Na+ ion is exchanged for each Mg2+. [fMg2+]i recovery was complete even if the membrane potential was depolarised to 0 mV or if superfusate [Mg2+] was increased to 3 mM. Recovery was rapid in normal Tyrode (0.3 min(-1)) with a Q10 of 2.2. It was completely inhibited by 200 microM imipramine but was unaffected by 20 microM KB-R7943 or 1 microM SEA0400, suggesting the Na+ /Ca2+ antiporter is not involved. Membrane depolarisation by increasing superfusate [K+] to 70 mM, or voltage clamp to 0 mV, increased recovery rate in Na+ containing solutions more than threefold. We conclude [fMg2+]i recovery is by Mg2+ efflux on a 1 Na+:1 Mg2+ antiport.
authors.affiliation: Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, EH8 9XD, Scotland, UK.
authors.forename: Hasan A
authors.initials: HA
authors.lastname: Almulla
authors.forename: Peter G
authors.initials: PG
authors.lastname: Bush
authors.forename: Michael G
authors.initials: MG
authors.lastname: Steele
authors.forename: Peter W
authors.initials: PW
authors.lastname: Flatman
authors.forename: David
authors.initials: D
authors.lastname: Ellis
mesh_terms: D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D000814:Aniline Compounds / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D017920:Antiporters / Q000378:metabolism*; D007099:Imipramine / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000502:physiology; D010647:Phenyl Ethers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors; D013696:Temperature; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D018759:Adrenergic Uptake Inhibitors; D000814:Aniline Compounds; D000889:Anti-Arrhythmia Agents; D017920:Antiporters; D010647:Phenyl Ethers; C430918:SEA 0400; D019831:Sodium-Calcium Exchanger; C046250:sodium-magnesium antiporter; D012964:Sodium; D013890:Thiourea; D008274:Magnesium; D007099:Imipramine