OBJECTIVETo investigate the effect and mechanism of emodin for regulating aquapoin-2 (AQP2) in NRK cells cultured in vitro.

METHODSExperiments on NRK cells cultured with alpha-DMEM medium in vitro were conducted in two steps. (1) Cells were randomly divided into 4 groups: the control group, and the three emodin treated groups treated with different dosages of emodin (5, 10 and 20 mg/L) respectively. After 24 h treatment, the location of AQP2 was decided by indirect immunofluorescene, and the AQP2 protein and mRNA expression levels were detected by Western blot and semiquantive RT-PCR. (2) Cells were randomly divided into 4 groups, the control group, and the three treated groups treated respectively with 10 mg/L 8-Bromo-cAMP, 20 mg/L emodin, and 20 mg/L emodin +10 mg/L 8-Bromo-cAMP. The activity of protein kinase A (PKA) in NRK cells after 24 h treatment was determined with non-radioactive detecting method.

RESULTSAQP2 was located at the cell membrane of NRK cells. Western blot and semiquantitive RT-PCR found that AQP2 protein and mRNA expressions were significantly decreased in NRK cells of groups treated by 10 mg/L and 20 mg/L emodin (P < 0.05). PKA activity determination showed significantly decreased phosphorylation level of PKA in NRK cells of groups treated with 20 mg/L emodin group (P < 0.05).

CONCLUSIONEmodin can inhibit the genetic transcription and the translation of AQP2 gene in NRK cells, which demonstrates that the change of AQP2 expression regulated by emodin may be correlated with the diuresis effect of rhubarb, and it is likely that the regulation is going through PKA signal pathway.