[Mechanism of potassium channel in hypoxia-ischemic brain edema: experiment with neonatal rat astrocyte].

Objective: To investigate the mechanism of potassium channel in brain edema caused by hypoxia-ischemia (HI).

Methods: Astrocytes were obtained from 3-day-old SD rats, cultured, and randomly divided into 2 groups: normoxia group, cultured under normoxic condition, and hypoxic-ischemic group, cultured under hypoxic-ischemic condition. The cell volume was measured by radiologic method. Patch-clamp technique was used to observe the electric physiological properties of the voltage-gated potassium channels (Kv) in a whole cell configuration, and the change of voltage-gated potassium channel current (IKv) was recorded in cultured neonatal rat astrocyte during HI. Aquaporin 4 (AQP4) expression vector was constructed from pSUPER vector and transfected into the astrocytes (AQP4 RNAi) to construct AQP4 knockdown (AQP4-/-) cells. cellular volume was determined using [3H]-3-O-methyl-D-glucose uptake in both AQP4-/- and AQP4+/+ cells under the condition of HI. Real time PCR and Western blotting were used to detect the mRNA and protein expression of AQP4.

Results: The percentages of the AQP4+/+ and AQP4-/- astrocyte volumes in the condition of HI for 0.5, 1, 2, and 4 h were 104+/-7, 109+/-6, 126+/-12, and 152+/-9 times, and 97+/-7, 105+/-9, 109+/-7, and 132+/-6 times as those of their corresponding control groups (all P<0.05), thus showing that the cellular volume of both AQP4+/+ and AQP4-/- astrocytes significantly increased during HI and the degrees of edema mediated by AQP4 knockdown at different time points were all significantly milder (all P<0.05). The current density values at the time points 0.5, 1, 2, and 4 h of the HI group were 107+/-9, 91+/-10, 76+/-6, 37+/-11, respectively, compared to that of the control group of 116+/-8, showing a tendency of time-dependent decreasing manner (all P<0.05).

Conclusion: During HI, the downregulation of outward potassium (K+) conductance may prevent the emission of intracellularly accumulated K+ ions, thus resulting in osmotically derived water influx into astrocytes via aquaporin-4 and then cell swelling.