Magnesium exchange in rat ventricle

Abstract

SUMMARY1. The exchange of cellular Mg with external 28Mg in the rat left ventricle was measured in vivo and, under conditions approximating a steady state, in an isolated, working rat heart perfused and contracting at 36-38°C.2. About 98 % of cellular Mg exchanged at a single rate.3. The rate of exchange in vivo was the same as that observed in independent in vitro measurements of the influx and efflux at the physiological external Mg2+ concentration of 0-56 mm. The rate was 0-15 + 0-02 mmole/(kg dry ventricle. min) or 0-21 + 0-02 p-mole/(cm2.seC).4. In the perfused heart the dependence of the influx on the external Mg concentration was hyperbolic with an apparent Vmax of 0-31 + 0-04 mmoles/(kg dry weight. min) and an apparent K_ of 0-57 + 0-08 mM.5. The Mg efflux into a solution containing 2-8 mM-Mg was markedly faster than that into a Mg-free solution.6. These results are interpreted as consistent with a carrier-mediated transport of Mg across the plasma membrane.

Effects of magnesium on contractile activation of skinned cardiac cells.

“…The second hypothesis is supported by other arguments, which are set forth in another article (Fabiato & Fabiato, 1975). It is reasonable to assume that the physiological intracellular free [Mg2+] is between 1040 and 100 M (Page & Polimeni, 1972). Even in the presence of a free…”

“…Cardiac tissue contains a large concentration of total Mg (Page & Polimeni, 1972). However, the exact role of free [Mg2+] in excitationcontraction coupling is difficult to study in intact cells.…”

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

“…The ATP concentration in ferret is 7-5 mm (Allen, Morris, Orchard & Pirolo, 1985) and with a total Mg2`concentration of 17 3 mm (Page & Polimeni, 1972) some 42 % of the total Mg2+ will be bound to ATP. It was thus of some interest to measure the free Mg2+ under conditions when the ATP concentration was reduced; not only should the binding for Mg2+ be reduced but if Mg2+ extrusion depends on ATP (Liidi & Schatzmann, 1987) then extrusion could also be reduced.…”

Angiotensin II and Vasopressin Modulate Intracellular Free Magnesium in Vascular Smooth Muscle Cells through Na+-dependent Protein Kinase C Pathways

“…Although mechanisms involved in the maintenance of [Mg 2ϩ ] i at optimal concentrations are unclear, it is apparent that multiple pathways are probably involved. Magnesium enters cells passively along a concentration gradient (15) and by facilitated diffusion (16) and is extruded from cells via two possible transporters, Na ϩ /Mg 2ϩ exchange and Mg 2ϩ -ATPase (13,17). The Na ϩ /Mg 2ϩ exchanger was first demonstrated in the squid giant axon where Na ϩ moving into the cell down its electrochemical gradient is coupled to Mg 2ϩ moving out of the cell (18).…”