Intracellular free magnesium and its regulation, studied in isolated ferret ventricular muscle with ion‐selective microelectrodes

Abstract

SUMMARYIntracellular free magnesium ([Mg2+]

Intracellular magnesium transport and regulation in epithelial secretory cells

“…From our studies using dual wavelength fluorimetry with Magfura-2, it would appear that resting [Mg 2+ ] i in both rat and mouse pancreatic acinar cells is about 0.8 mM (41)(42)(43)(44)(45)(46), which is very similar to the value found by other authors with the same technique in pancreatic beta cells (35). Accordingly, using this approach, [Mg 2+ ] i between 0.9 and 1 mM have been reported in heart tissue as measured with Mg 2+ -selective microelectrodes (47)(48)(49) as well as in skeletal muscle as determined by 31 P NMRs (50). We observed a lower [Mg 2+ ] i (around 0.5 mM) in Magfura-loaded rat parietal cells (51), and studies with this probe give basal [Mg 2+ ] i values of approximately 0.25 mM for human platelets (37), 0.30-0.35 mM for human lymphocytes (52) and sublingual acinar cells (38,39), and 0.5 mM for renal epithelial cells and isolated hepatocytes (29,53).…”

Effects of Membrane Potential on Na+ -Dependent Mg2+ Extrusion from Rat Ventricular Myocytes.

“…

In cardiac myocytes, the cytoplasmic-free concentration of Mg 2ϩ ([Mg 2ϩ ] i ) is maintained at or slightly lower than 1.0 mM [1][2][3][4], a level several hundred fold lower than that expected from its passive distribution. It follows that Mg 2ϩ must be actively extruded from the cells to counterbalance Mg 2ϩ influx driven by the electrochemical gradient across the cell membrane.

As it is such an active extrusion pathway, it has been postulated that a Na ϩ -Mg 2ϩ exchange that utilizes energy from Na ϩ influx plays an important role in cardiac myocytes [5][6][7] as well as in other cell types (for review, see Flatman [8] and Romani and Scarpa [9]).

However, experimental evidence of the Na ϩ -Mg 2ϩ exchange in cardiac myocytes is controversial [3,4,10], and detailed properties of the transport still remain largely unknown.

The present study was aimed to determine, under control of the membrane potential, if Na ϩ -Mg 2ϩ exchange plays an essential role in cardiac myocytes, and how the membrane potential, over a wide range, modulates the transport of Mg 2ϩ across the cell membrane.

…”

“…In cardiac myocytes, the cytoplasmic-free concentration of Mg 2ϩ ([Mg 2ϩ ] i ) is maintained at or slightly lower than 1.0 mM [1][2][3][4], a level several hundred fold lower than that expected from its passive distribution. It follows that Mg 2ϩ must be actively extruded from the cells to counterbalance Mg 2ϩ influx driven by the electrochemical gradient across the cell membrane.…”

“…However, experimental evidence of the Na ϩ -Mg 2ϩ exchange in cardiac myocytes is controversial [3,4,10], and detailed properties of the transport still remain largely unknown.…”

Proceedings of the Physiological Society, 14‐15 February 1992, Bristol Meeting: Communications

“…Thus other explanations for their inhibitory actions in this system need to be sought. Intracellular magnesium may be extruded via a Na-Mg exchange in guineapig myocardium (Fry, 1986), although no evidence for such a mechanism was found in ferret ventricular muscle (Buri & McGuigan, 1990). In the present study, magnesium regulation in guinea-pig myocardium has been re-investigated using improved Na'-and Mg2+-selective microelectrodes (ETH 227 and 5214,respectively) and the new fluorochrome Mag-Fura-5.…”