Expression of aquaporin water channels in rat vagina: potential role in vaginal lubrication.

INTRODUCTION

Aquaporins (AQPs) are membrane proteins that facilitate water movement across biological membranes. There has been little research on the role of AQPs in the female sexual arousal response.

AIM

The purposes of this study were to investigate the localization and functional roles of AQP1, AQP2, and AQP3 in rat vagina.

METHODS

Female Sprague-Dawley rats (230-240 g, N = 20) were anesthetized. The vaginal branch of the pelvic nerve was stimulated for 60 seconds (10 V, 16 Hz, 0.8 ms), and the animals were sacrificed either immediately or 5 minutes later. The expression and cellular localization of AQP1, 2, and 3 were determined by Western blot and immunohistochemistry of the vagina. The intracellular membrane and plasma membrane fractions of the proteins in vaginal tissue were studied by immunoblot analysis with the differential centrifugation.

MAIN OUTCOME MEASURES

The expression and cellular localization of AQPs, and pelvic nerve stimulation induced translocation of AQPs in rat vaginal tissue.

RESULTS

Immunolabeling showed that AQP1 was mainly expressed in the capillaries and venules of the vagina. AQP2 was expressed in the cytoplasm of the epithelium, and AQP3 was mainly associated with the plasma membrane of the vaginal epithelium. AQPs were found to be present primarily in the cytosolic fraction of untreated tissues. The translocation of AQP1 and 2 isoforms from the cytosolic compartment to the membrane compartment was observed immediately after nerve stimulation and had declined at 5 minutes after nerve stimulation, while the subcellular localization of AQP3 was not changed by nerve stimulation.

CONCLUSIONS

These results showed a distinct localization of AQPs in the rat vagina. Pelvic nerve stimulation modulated short-term translocation of AQP1 and 2. These results imply that AQPs may play an important role in vaginal lubrication.