Blockade by magnesium of sodium currents in acutely isolated hippocampal CA1 neurons of rat.

The effects of magnesium (MgSO(4)) on sodium currents (Na(+) currents) in freshly dissociated rat hippocampal neurons were studied using the whole-cell patch clamp techniques. MgSO(4) caused a concentration-dependent and voltage-dependent reversible decrease of Na(+) currents. The half-blocking concentration (IC(50)) of MgSO(4) on Na(+) currents was 4.05 mM. But the action was frequency-independent. In addition, 4 mM MgSO(4) shifted the steady state activation curve of Na(+) currents toward positive potential (control V(h)=-55.83+/-6.79 mV, MgSO(4)V(h)=-34.15+/-6.18 mV, n=8, P</=0.01 without changing the slope factor). However, the steady state inactivation curve was not affected. These results suggested that blockade of MgSO(4) on Na(+) currents might be an interpretation for its neuroprotection against damages induced by ischemia and oxygen deprivation.