Differential Modulation of Intracellular Ca2+ Responses Associated with Calcium-Sensing Receptor Activation in Renal Collecting Duct Cells
In this work, we studied G protein-coupled Extracellular Calcium Sensing Receptor (CaR) signaling in mouse cortical collecting duct cells (MCD4) expressing endogenous CaR. Intracellular [Ca<sup>2+</sup>] measurements performed with real time video imaging revealed that CaR stimulation with 5mM Ca<sup>2+</sup>, 300µM Gd<sup>3+</sup> and with 10µM of specific allosteric modulator NPS-R 568, all resulted in an increase in [Ca<sup>2+</sup>]<sub>i</sub> although displaying different features. Specifically, Ca<sup>2+</sup> as well as stimulation with NPS-R 568 induced a rapid peak of [Ca<sup>2+</sup>]<sub>i</sub> while stimulation with Gd<sup>3+</sup> induced transient intracellular Ca<sup>2+</sup> oscillations. PLC inhibition completely abolished any [Ca<sup>2+</sup>]<sub>i</sub> increase after stimulation with CaR agonists. Inhibition of Rho or Rho kinase (ROK) abolished [Ca<sup>2+</sup>]<sub>i</sub> oscillations induced by Gd<sup>3+</sup>, while the peak induced by high Ca<sup>2+</sup> was similar to control. Conversely, emptying the intracellular calcium stores abolished the response to Gd<sup>3+</sup>. On the other hand, the inhibition of calcium influx did not alter calcium changes. We conclude that in our cell model, CaR stimulation with distinct agonists activates two distinct transduction pathways, both PLC-dependent. The transient cytosolic Ca<sup>2+</sup> oscillations produced by Gd<sup>3+</sup> are modulated by Rho-Rho kinase signaling, whereas the rapid peak of intracellular Ca<sup>2+</sup> in response to 5mM [Ca<sup>2+</sup>]<sub>o</sub> is mainly due to PLC/IP3 pathway activation.