[Effect of hypotonic medium on expression of aquaporin-4 in astrocytes]

To investigate the expression of aquaporin-4 (AQP4) and its role in cultured rat astrocytes after exposure to hypotonic medium.

Rat cerebral cortical astrocytes from 2 days newborn Wistar rats were undergone the pure culture. The cells were divided into control group and hypotonic groups randomly, in which group was examined at interval times of 3, 6, 12 and 24 h, respectively (n = 6), and its model of cell edema was established by exposed to hypotonic medium. The cells of the control group were cultured in normal culture medium. Inverted microscope and transmission electron microscope were used to observe the cells changes. The reactivity and rules of AQP4mRNA and protein expression of astrocyte to hypotonic medium were studied by RT-PCR, immunocytochemistry, the activity of LDH and imaging analysis.

There was no significant change in the control group. After astrocytes cultured for 3, 6, 12, 24 h with hypotonic medium (268, 254, 240 mmol/L), the astrocytes showed typical features of cell edema, especially in lower osmolality group. The activity of LDH showed a significant change than those in the control group after astrocytes exposed to hypotonic medium (P < 0.05). RT-PCR and immunocytochemistry analysis confirmed that the expression of AQP4mRNA and protein was remarkably increased (P < 0.05), up-graduated expression of AQP4 was correlated with hypotonic medium and time dependent manner. The AQP4mRNA expression showed a positive relationship with the AQP4 protein expression during the astrocytes edema formation (r > 0.8369, P < 0.05).

Hyponotic medium could induce cell edema and expression of AQP4mRNA and protein increased, and vibility of astrocytes inhibited. The AQP4 expression showed a positive relationship with the osmolality. The results suggest that AQP4 participated in the brain edema formation.