Abstract: AIMTo study the effect of magnesium sulfate on transient outward K⁺current (I_A) and delayed rectifier K⁺current (I_K) in freshly dissociated hippocampal neurons of rats. METHODSThe whole-cell patch clamp techniques were used. RESULTSMagnesium sulfate reversibly reduced the amplitudes of I_A and I_K in a concentration-dependent and voltage-dependent, but not frequency-dependent manner. Half-blocking concentration (IC₅₀) on I_A and I_K were 6.30 mmol·L^-1 and 7.60 mmol·L^-1, respectively. Magnesium sulfate (6 mmol·L^-1) affected the activation process of I_A and I_K. Before and after application of the drug, the half-activation voltages of I_A were (7±6) mV and (-7±11) mV (N=10, P<0.01), and the half-activation voltages of I_K were (20±6) mV and (28±4) mV (N=10, P<0.01), but the slope factors were not changed. In addition, magnesium sulfate (6 mmol·L^-1) also affected the inactivation process of I_A. Before and after application of the drug, the half-inactivation voltages of I_A were (-65±5) mV and (-89±6) mV (N=10, P<0.01). CONCLUSIONMagnesium sulfate inhibited I_A and I_K in freshly dissociated hippocampal neurons of rats, which might contribute to protect the central neuronal system (CNS) against damages induced by ischemia and oxygen deprivation.