The exchange of radioactive magnesium in erythrocytes of several species

Abstract

A previous publication (Rogers and Mahan, '59) has described the exchange of radioactive magnesium in various tissues of the rat. It was found that there are two principal exchange rates, one with a turnover time of 1.2 hours and another with about 25 hours. In myocardium, liver and kidney, only the fast component was apparent and the specific activity of the tissue magnesium reached that of the plasma magnesium in three hours. In the other tissues studied (brain, skeletal muscle, testes and red cells), more than half of the magnesium exchanged at the slower rate. It was of interest to compare the exchange of radioactive magnesium in the red cells of other species both in vivo and in vitro, and in rat cells in nitro. METHODSFor the in vivo studies, isotonic solutions of MgC1, containing Mg" were injected i/v into dogs and cats. Blood samples were drawn at intervals from the catheterized femoral artery. In the in vitro studies, the radioactive solution was added to whole blood of rats, dogs, cats, cattle and man, which was then incubated at 38°C with gentle agitation under 5% carbon dioxide in oxygen. Samples were drawn at intervals.In each case, the blood was immediately centrifuged at a standard rate for 4 minutes and the plasma removed for radioactive and chemical assay. The cells were washed with ice-cold isotonic saline, centrifuged for 4 minutes and then the washing and centrifugation were repeated once more. An aliquot comprising 0.5 ml of washed, packed red cells was added to 0.5 ml water in a tube which was then placed in a well-type scintillation counter. After counting, 2 ml of 10% trichloracetic acid was added to the hemolysate and centrifuged in the same tube. The supernatant fluid was analyzed for magnesium by the method of Orange and Rhein ('51). Plasma samples received similar treatment. The results are expressed as the "relative specific activity" (r.s.a.) which is the ratio Specific activity of red cell Mg Specific activity of plasma MgWhen this ratio is equal to 1.0, equilibration is complete. An advantage of this method of expressing the data is that variations in the packing of the cells are unimportant because the count rate and magnesium content are determined for each 1 ml sample of hemolysate. In some instances the hemolysate was centrifuged and the supernatant counted (without the cell ghosts). In each case the count rate was identical with that in the original sample, indicating that the Mgz* content of the "membranes" was negligible. RESULTS AND DISCUSSIONThe in vivo and in vitro equilibration of the magnesium in cat red cells with that in the plasma is shown in figure 1; almost identical curves were obtained for dog and rat cells. The pattern of equilibration in rat erythrocytes in vivo, which was previously described (Rogers and Mahan, '59), was determined by sacrificing isotopeinjected animals in series. All the results obtained in vivo tend to lie on less smooth curves than those in vitro and this may be partly attributed to the rapid biological decay of the plasma magnesium radioac...

The Effect of Dialysate Magnesium on Plasma and Erythrocyte Magnesium and Potassium Concentrations during Maintenance Haemodialysis

“…Our present results confirm their findings [14] that a single dialysis has no demonstrable effect on erythrocyte magnesium con centrations, unlike the concurrent plasma levels. This finding accords with the orthodox view that erythrocytes are relatively impermeable to magnesium ions [20,26], the immediate changes during one dialysis being seen only in the plasma magnesium.…”

Magnesium buffering in intact human red blood cells measured using the ionophore A23187.

“…If anything, however, red cells seem to lose magnesium as they age (Bernstein, 1959). Rogers (1961) and Ginsburg et al (1962) have shown that 28Mg exchanges extremely slowly between medium and red cells which suggests that the membrane has a low permeability to magnesium. Moreover, it has been shown here that red cell magnesium content does not depend on the composition of the media, at least in the short term.…”

“…The plasma membrane of human red blood cells has such a low permeability to magnesium (Rogers, 1961;Ginsburg, Smith, Ginsburg, Reardon & Aikawa, 1962) that it was not possible until recently to alter the magnesium content of red cells in a controllable manner without disruption of the cell membrane. The dependence of fundamental physiological functions on the concentration of magnesium was therefore studied using reconstituted ghosts (Bodemann & Hoffman, 1976) and broken membrane fragments (Dunham & Glynn, 1961;Schatzmann, 1977).…”

Magnesium transport in magnesium-loaded ferret red blood cells

“…Red blood cells from many species have a very low Mg permeability [13,25]. For instance, Mg efflux from fresh human and chicken red blood cells is too low to measure easily [1,18,24].…”