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1 Leibniz-Institut fur Molekulare Pharmakologie, Berlin, Germany
2 Leibniz-Institut fur Molekulare Pharmakologie, Berlin, Germany; Charite-Universitatsmedizin, Institut fur Pharmakologie, Campus Bejamin Franklin, Berlin, Germany
3 Leibniz-Institut fur Molekulare Pharmakologie, United States; Charite-Universitatsmedizin, Institut fur Pharmakologie, Campus Bejamin Franklin, Berlin, Germany
* To whom correspondence should be addressed. E-mail: klussmann{at}fmp-berlin.de.
Water reabsorption in the renal collecting duct is regulated by arginine-vasopressin (AVP). AVP induces the insertion of the water channel aquaporin-2 (AQP2) into the plasma membrane of principal cells, thereby increasing the osmotic water permeability. The redistribution of AQP2 to the plasma membrane is a cAMP-dependent process and thus a paradigm for cAMP-controlled exocytic processes. Using primary cultured rat inner medullary collecting duct (IMCD) cells we show that the redistribution of AQP2 to the plasma membrane is accompanied by the reorganisation of microtubules and the redistribution of the small GTPase Rab11. In resting cells, AQP2 is colocalized with Rab11 perinuclearly. AVP induced the redistribution of AQP2 to the plasma membrane and of Rab11 to the cell periphery. The redistribution of both proteins was increased when microtubules were depolymerised by nocodazole. In addition, the depolymerisation of microtubules prevented the perinuclear positioning of AQP2 and Rab11 in resting cells, which was restored if nocodazole was washed out and microtubules repolymerised. After internalization of AQP2, induced by removal of AVP, forskolin triggered the AQP2 redistribution to the plasma membrane even if microtubules were depolymerised and without the previous positioning of AQP2 in the perinuclear recycling compartment. Collectively, the data indicate that microtubule-dependent transport of AQP2 is predominantly responsible for trafficking and localization of AQP2 inside the cell after its internalization but not for the exocytic transport of the water channel. We also demonstrate that cAMP-signaling regulates the localization of Rab11-positive recycling endosomes in renal principal cells.
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