Intracellular Mg2+ regulation in voltage-clamped Helix aspersa neurones measured with mag-fura-2 and Mg(2+)-sensitive microelectrodes.
The extrusion mechanism for intracellular Mg2+ was investigated in voltage-clamped snail neurones using Mg(2+)-sensitive microelectrodes and mag-fura-2. The intracellular free magnesium ion concentration ([Mg2+]1) of snail neurones voltage clamped to -60 mV was estimated to be 0.57 +/- 0.06 mM (mean +/- S.E.M.; n = 12) using Mg(2+)-sensitive microelectrodes and 0.62 +/- 0.05 mM (n = 15) using mag-fura-2. Raising extracellular MgCl2 from 5 to 20 mM caused an average increase in [Mg2+]1 of 0.25 +/- 0.04 mM (n = 7). In three experiments, removing extracellular Mg Cl2 caused an average decrease in [Mg2+]1 of 0.1 mM. Replacing extracellular Na+ with N-methyl-D-glucamine (NMDG) caused a rise in [Mg2+]1 of 1.8 +/- 0.5 mM (n = 7); [Mg2+]1 recovered to resting levels when extracellular Na+ was restored. Iontophoretic injections of MgCl2 were used to raise [Mg2+]1. The rate of recovery from such increases in [Mg2+]1 ¿calculated from the slope of the recovery was inhibited by 85-100% (n = 5) in the absence of extracellular Na2+ compared with control conditions. Raising extracellular Ca2+ from 7 to 35 mM caused a reversible rise in [Mg 2+]1 of 0.4 +/- 0.05 mM (mean +/- S.E.M., n = 7). It was concluded that in snail neurones the main mechanism for [Mg2+]1 extrusion is a Na(+)-Mg2+ exchanger which may be partially inhibited be high extracellular Ca2+ concentrations.
Department of Physiology, School of Medical Sciences, University of Bristol, UK. helen.kennedy@bristol.ac.uk
H J
HJ
Kennedy
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004594:Electrophysiology; D005456:Fluorescent Dyes / Q000378:metabolism; D016257:Fura-2 / Q000031:analogs & derivatives / Q000378:metabolism; D006372:Helix, Snails / Q000502:physiology*; D007424:Intracellular Fluid / Q000502:physiology*; D008274:Magnesium / Q000378:metabolism*; D008536:Meglumine / Q000031:analogs & derivatives; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000494:pharmacology
D005456:Fluorescent Dyes; C058776:2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic acid; D008536:Meglumine; D012964:Sodium; D008274:Magnesium; D002118:Calcium; D016257:Fura-2