NAADP‐induced Ca 2+ signaling in response to endothelin is via the receptor subtype B and requires the integrity of lipid rafts/caveolae

We have investigated the role of NAADP‐mediated Ca 2+ mobilization in endothelin (ET) signaling via endothelin receptor subtype A (ETA) and endothelin receptor subtype B (ETB) in rat peritubular smooth muscle cells. Microinjection and extracellular application of NAADP were both able to elicit Ca 2+ release which was blocked by inhibitory concentrations of NAADP, by impairing Ca 2+ uptake in acidic stores with bafilomycin, and by thapsigargin. Ca 2+ release in response to selective ETB stimulation was abolished by inhibition of NAADP signaling through the same strategies, while these treatments only partially impaired ETA‐dependent Ca 2+ signaling, showing that transduction of the ETB signal is dependent on NAADP. In addition, we show that lipid rafts/caveolae contain ETA, ETB, and NAADP/cADPR generating enzyme CD38 and that stimulation of ETB receptors results in increased CD38 activity; interestingly, ETB‐ (but not ETA‐) mediated Ca 2+ responses were antagonized by disruption of lipid rafts/caveolae with methyl‐β‐cyclodextrin. These data demonstrate a primary role of NAADP in ETB‐mediated Ca 2+ signaling and strongly suggest a novel role of lipid rafts/caveolae in triggering ET‐induced NAADP signaling. J. Cell. Physiol. 216: 396–404, 2008. © 2008 Wiley‐Liss, Inc.