Cl. Chou et al., Regulation of aquaporin-2 trafficking by vasopressin in the renal collecting duct - Roles of ryanodine-sensitive Ca2+ stores and calmodulin, J BIOL CHEM, 275(47), 2000, pp. 36839-36846
In the renal collecting duct, vasopressin increases osmotic water permeabil
ity (P-f) by triggering trafficking of aquaporin-2 vesicles to the apical p
lasma membrane. We investigated the role of vasopressin-induced intracellul
ar Ca2+ mobilization in this process. In isolated inner medullary collectin
g ducts (IMCDs), vasopressin (0.1 nM) and 8-(4-chlorophenylthio)-cAMP (0.1
mM) elicited marked increases in [Ca2+](i) (fluo-4), Vasopressin-induced Ca
2+ mobilization was completely blocked by preloading with the Ca2+ chelator
BAPTA, In parallel experiments, BAPTA completely blocked the vasopressin-i
nduced increase in P-f without affecting adenosine 3',5'-cyclic monophospha
te (cAMP) production. Previously, we demonstrated the lack of activation of
the phosphoinositide-signaIing pathway by vasopressin in IMCD, suggesting
an inositol 1,4,5-trisphosphate-independent mechanism of Ca2+ release. Evid
ence for expression of the type I ryanodine receptor (RyR1) in IMCD was obt
ained by immunofluorescence, immunoblotting, and reverse transcription-poly
merase chain reaction, Ryanodine (100 muM), a ryanodine receptor antagonist
, blocked the arginine vasopressin-mediated increase in P-f and blocked vas
opressin-stimulated redistribution of aquaporin-2 to the plasma membrane do
main in primary cultures of IMCD cells, as assessed by immunofluorescence i
mmunocytochemistry. Calmodulin inhibitors (W7 and trifluoperazine) blocked
the P-f response to vasopressin and the vasopressin-stimulated redistributi
on of aquaporin-2. The results suggest that Ca2+ release from ryanodine-sen
sitive stores plays an essential role in vasopressin-mediated aquaporin-2 t
rafficking via a calmodulin-dependent mechanism.