In
autosomal dominant polycystic kidney disease (
ADPKD), binding of AVP to the
V2 receptor (V2R) increases cAMP and accelerates
cyst growth by stimulating cell proliferation and Cl(-)-dependent fluid secretion. Basal cAMP is elevated in human
ADPKD cells compared with normal human kidney (NHK) cells. V2R
mRNA levels are elevated in
ADPKD cells; however, AVP caused a greater increase in global cAMP in NHK cells, suggesting an intrinsic difference in cAMP regulation. Expression, regulatory properties, and receptor coupling of specific
adenylyl cyclases (ACs) provide temporal and spatial regulation of the cAMP signal.
ADPKD and NHK cells express mRNAs for all nine ACs. Ca(2+)-inhibited ACs 5 and 6 are increased in
ADPKD cells, while Ca(2+)/CaM-stimulated ACs 1 and 3 are downregulated. ACs 1, 3, 5, and 6 were detected in
cyst cells in situ, and codistribution with
aquaporin-2 suggests that these
cysts were derived from collecting ducts. To determine the contribution of CaM-sensitive ACs to AVP signaling, cells were treated with
W-7, a CaM inhibitor.
W-7 decreased AVP-induced cAMP production and Cl(-) secretion by
ADPKD cells.
CaMKII inhibition increased AVP-induced cAMP, suggesting that cAMP synthesis is mediated by AC3. In contrast, CaM and
CaMKII inhibition in NHK cells did not affect AVP-induced cAMP production. Restriction of intracellular Ca(2+) switched the response in NHK cells, such that CaM inhibition decreased AVP-induced cAMP production. We suggest that a compensatory response to decreased Ca(2+) in
ADPKD cells switches V2R coupling from Ca(2+)-inhibited ACs 5/6 to Ca(2+)/CaM-stimulated AC3, to mitigate high cAMP levels in response to continuous AVP stimulation.