Abstract
Filamentous actin (F‐actin) depolymerization is critical for vasopressin mediated AQP2 membrane accumulation. In this study, we compared the F‐actin polymerization state in MDCK and LLC‐PK1 cells with or without AQP2 transfection using a rhodamine‐phalloidin assay. In AQP2 expressing cells, the F‐actin level was significantly decreased 10% by vasopressin and forskolin (VP/FK); from 1.00 ± 0.02 to 0.90 ± 0.02 (n = 5, P < 0.001) at 60 min in AQP2 MDCK cells, and from 1.00±0.02 to 0.90±0.04 (n = 5, P < 0.001) at 20 min in AQP2 LLC‐PK1 cells. However, the F‐actin decrease induced by VP/FK was not observed in untransfected cells; from 1.00 ± 0.02 to 0.99 ± 0.03 (n = 5, P = 0.53) in MDCK cells, from 1.00±0.03 to 0.99±0.04 (n = 5, P = 0.59) in LLC‐PK1 cells. Furthermore, the extent of F‐actin depolymerization by VP/FK in AQP2 expressing cells was correlated with the AQP2 expression level. These results show that vasopressin mediated F‐actin depolymerization requires AQP2. This function of AQP2 probably involves interaction with regulatory components of the actin cytoskeleton, including, but not limited to, tropomyosin‐5b (Noda, Sasaki et al) and ERM proteins (Tamma, Valenti et al).
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