The extracellular calcium-sensing receptor is expressed in rat microglia and modulates an outward K+ channel

The calcium-sensing receptor (CaR) is a G protein-coupled receptor that "senses" extracellular calcium ions (Ca-o(2+)) as an extracellular first messenger. In this report, we have shown that the CaR is expressed in primary cultures of microglial cells derived from rat brain as assessed by RT-PCR using four CaR-specific primer pairs followed by sequencing of the amplified products, by northern blot analysis using a CaR-specific probe, as well as by immunocytochemistry and western analysis utilizing a specific polyclonal anti-CaR antiserum. In addition, raising Ca-o(2+) from 0.75 to 3.0 mM or addition of the polycationic CaR agonist neomycin or a "calcimimetic" CaR activator (R-467; NPS Pharmaceuticals) increased the open state probability (P-o) of a Ca+-activated K+ channel having a unitary conductance of 84 +/- 4 pS, indicating that the channel is modulated by the CaR, Therefore, our data strongly suggest that a functional CaR is expressed in cultured rat microglia, similar to that in parathyroid gland and kidney, which could potentially play an important role(s) in regulating microglial function.