Serine-O-phosphate has affinity for type IV, but not type I, metabotropic glutamate receptor

L-serine-O-phosphate (L-SOP) has been reported to antagonize phosphoinositide (PI) hydrolysis in slices of rat brain as stimulated by agonists of the metabotropic glutamate receptor (mGluR). In the present study, the affinity of L-SOP was examined in a baby hamster kidney (BHK) cells expressing subtype mGluR1 or mGluR4 of the mGluR family. L-SOP or D-SOP (3 mM) did not inhibit PI-hydrolysis as stimulated by 10 microM glutamate in BHK cells expressing mGluR1. However, L-SOP was a potent agonist at the mGluR4 subtype (IC50 = 4.4 +/- 1.4 microM), which is negatively coupled to adenylate cyclase, while D-SOP was weakly active (IC50 = 1260 +/- 190 microM).