Intracellular free magnesium in frog skeletal muscle studied with a new type of magnesium-selective microelectrode: interactions between magnesium and sodium in the regulation of [Mg]i.
The application of a new type of intracellular magnesium-selective microelectrode based on the neutral carrier ETH5214 to measure intracellular free magnesium ([Mg]i) in frog skeletal muscle fibers is reported. At room temperature (18-20 degrees C) the average values for [Mg]i was 0.93 mmol/l (pMgi = 3.03 +/- 0.42, SD; n = 38 experiments). The regulation of [Mg]i was studied by measuring [Mg]i and [Na]i with ion-selective microelectrodes during alterations of the membrane potential and the transmembrane sodium and magnesium gradients. Depolarization by increasing external [K] from 2.5 mmol/l to 12.5 mmol/l did not significantly influence [Mg]i. Increasing extracellular [Mg] from 1 mmol/l to 10 and 20 mmol/l caused a concentration-dependent rise in [Mg]i and a decrease in [Na]i, whereas removal of external magnesium did not affect [Mg]i. Removal of external [Na] caused an increase in [Mg]i and a decrease of [Na]i. The results show that [Mg]i in frog skeletal muscle is not in thermodynamic equilibrium and suggest that a Na/Mg exchange mechanism may be involved in maintaining low levels of [Mg]i.
Blatter
L A
LA
Department of Pharmacology, Mayo Foundation, Rochester, MN 55905.
D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability / Q000502:physiology; D008024:Ligands; D008274:Magnesium / Q000378:metabolism* / Q000502:physiology; D008314:Malonates; D008564:Membrane Potentials / Q000502:physiology; D008839:Microelectrodes; D009132:Muscles / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D011896:Rana temporaria / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
D008024:Ligands; D008314:Malonates; C065247:ETH 5214; D012964:Sodium; D008274:Magnesium