A G protein-coupled, extracellular calcium (Ca(0)2+)-sensing receptor (CaR) cloned from parathyroid, kidney, and brain plays crucial roles in systemic calcium metabolism. In brain, the CaR is located in nerve terminals as well as in fiber tracts, where it may be expressed in glia. Moreover, there is Ca2+- and K+-dependent communication between axons and oligodendroglia. To investigate further the potential role of the CaR in oligodendroglia, we studied expression of CaR mRNA and protein as well as the effects of CaR agonists on cellular proliferation and Ca2+-activated K+ channel activity in immature rat oligodendrocytes in primary culture. Reverse transcriptase polymerase chain reaction and sequencing of CaR transcripts from oligodendrocytes revealed >99% sequence identity with the rat kidney CaR. Northern analysis demonstrated 7.5 and 4.1 kb transcripts in oligodendrocytes, similar to those in rat parathyroid and kidney, while Western analysis and immunocytochemistry with CaR-specific antisera showed the presence of CaR protein. Immunocytochemically, the CaR was colocalized with galactocerebroside in the cultured oligodendrocytes. Raising Ca(0)2+ from 1.8 to 4.8 mM or addition of the polycationic CaR agonist neomycin (300 microM) modestly but significantly increased [3H]-thymidine incorporation into oligodendrocytes. Elevating Ca(0)2+ from 0.75 to 3.0 mM or addition of 100 microM neomycin also produced 2-2.5-fold increases in the open state probability (Po) of an outward K+ channel with a unitary conductance of 88+/-5 pS. Taken together, our data show that the CaR is expressed in immature oligodendrocytes and may be functionally linked to cellular proliferation and an outward K+ channel potentially contributing to local ionic homeostasis in the vicinity of oligodendroglia.