Ionized magnesium in the homeostasis of cells: intracellular threshold for Mg(2+) in human platelets

SLC41 transporters--molecular identification and functional role

The solute carrier family 41 (SLC41) encompasses three members A1, A2, and A3. Based on their distant homology to the bacterial Mg²⁺ channel MgtE, all have been linked to Mg²⁺ transport. There is only very limited knowledge on the molecular biology and exact functions of SLC41A2 and SLC41A3. SLC41A1 is ubiquitously expressed and data on its functional and molecular properties, regulation, complex-forming ability, and spectrum of binding partners are available. SLC41A1 was recently identified as being the Na⁺/Mg²⁺ exchanger (NME)-a predominant Mg²⁺ efflux system. Mg²⁺-dependent and hormonal regulation of NME activity is now known to depend on the intracellular N terminus of SLC41A1 that is involved in Mg²⁺ sensing and contains phosphorylation sites for protein kinase (PK) A and PKC. Data showing a link between SLC41A1 and human disorders such as Parkinson's disease, nephronophthisis (induced by the null mutation c.698G>T in renal SLC41A1), and preeclampsia make the protein a candidate therapeutic target.

Electrolytes and pH changes in pre-eclamptic rats

BACKGROUND

Intracellular free calcium [Ca2+]i and magnesium [Mg2+]i ions play major roles in the mechanism of vascular smooth muscle (VSM) contraction. Although essential hypertension and abnormal intracellular homeostasis of these ions have long been recognized as major icons in the pathogenesis of pre-eclampsia, the underlying mechanism(s) remain poorly understood.

METHODS

Alterations of vascular smooth muscle and platelet intracellular cations [Ca2+]i, [Mg2+]i and [H+]i relative to plasma concentrations of these ions in nitric oxide synthase (NOS) blockade-induced models of pre-eclampsia have been evaluated in the present study.

RESULTS

Pregnant rats injected with the NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) developed a significantly elevated arterial blood pressure, proteinuria and other clinical parameters characteristic of pre-eclampsia compared to age-matched pregnant and non-pregnant rat controls that received the L-NAME vehicle only. Plasma total calcium concentration was significantly lower in pre-eclamptic rat models compared to normal pregnant rats (10.29+/-0.08 vs 10.67+/-0.18 mg/dl, p<0.05). A significant increase in plasma calcium was observed in pregnant controls compared to non-pregnant rats (10.67+/-0.18 vs 10.14+/-0.09 mg/dl, p<0.01). Plasma Ca2+ levels in pre-eclamptic rats were consistently lower than those of pregnant controls (5.69+/-0.09 vs 5.98+/-0.06 mg/dl, p<0.05). Resting levels of [Ca2+]i was significantly higher in pre-eclamptic rats than in pregnant controls. (351+/-45.2 vs 196+/-23.2 nmol/l, p<0.01). Blood pH was significantly increased in pre-eclamptic rats as compared to pregnant controls (7.16+/-0.02 vs 7.05+/-0.03, p<0.05). There was no significant difference in plasma and intracellular magnesium concentrations between the three rat groups.

CONCLUSIONS

These findings suggest that a significantly decreased plasma level of Ca2+ coupled with a concomitant increase in VSM [Ca2+]i concentrations and an altered blood pH are associated with pre-eclampsia in the pregnant rat. Routine monitoring of serum pH, Ca2+ and Mg2+ especially in the late third trimester, may have potential in the early detection of patients at risk for pre-eclampsia, and monitoring the progress of diverse therapeutic regimens during clinical management.