Sphingosylphosphorylcholine activates Gq, Gi-2, and Gi-3 in thyroid FRTL-5 cells: implications for the activation of calcium fluxes and Na+-H+ exchange.
In the present investigation of rat thyroid FRTL-5 cells, we show using reverse-transcriptase PCR that these cells express both Edg-1 and Edg-5. We show using a [35S]GTPgammaS-binding assay that sphingosylphosphorylcholine (SPC), which binds to both Edg-1 and EDG-5, activates Gq, Gi-2, and Gi-3 proteins. SPC potently increases intracellular free calcium concentrations ([Ca2+]i). This effect is mediated through both Gq and Gi proteins, as the mobilization of sequestered calcium was insensitive to pertussis toxin (i.e., mediated by Gq), while the SPC-evoked calcium entry was inhibited by pretreatment with pertussis toxin (i.e., mediated by Gi). Furthermore, SPC in a concentration-dependent manner increases intracellular pH in acidified cells via a Na+-H+ exchange mechanism. The enhanced activation of Na+-H+ exchange is independent of both an increase in [Ca2+]i and an activation of protein kinase C. The effect of SPC on Na+-H+ exchange is insensitive to pertussis toxin, suggesting an effect mediated via Gq.
D000818:Animals; D001483:Base Sequence; D001704:Biopolymers; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D017931:DNA Primers; D019204:GTP-Binding Proteins / Q000378:metabolism*; D017136:Ion Transport; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism