O-Phospho-L-serine

O-Phospho-L-serine is the immediate precursor to L-cystein in the serine synthesis pathway, and an agonist at the group III mGluR receptors (mGluR4, mGluR6, mGluR7, and mGluR8); O-Phospho-L-serine also acts as a weak antagonist for mGluR1 and a potent antagonist for mGluR2^[1]. In Vitro:O-Phospho-L-serine (l-SOP) weakly binds to mGluR1, and antagonizes the effects of l-glutamate. l-SOP activates the group III receptors (mGluR4, mGluR6, mGluR7, and mGluR8), but mGluR7 has much lower affinity for l-SOP than the other group III receptors and also displays lower efficacy for both ligands^[1]. O-Phospho-L-serine (l-SOP) generates enhanced intracellular calcium responses in mGluR4 transfected cells. l-SOP inhibits the l-glutamate mediated mGluR1 response, with a K_i of 1 mM; l-SOP displays a substantially more potent inhibition of mGluR2 activation, with a K_i of 1 μM, three orders-of-magnitude more potent than for mGluR1. l-SOP induces membrane potential changes in HEK/TRPC4 cells transfected with mGluR4 or mGluR6. l-SOP induces TRPC4β activation mediated by Gα_i/o proteins^[2]. O-Phospho-L-serine (L-SOP) inhibits Müller glia proliferation, without affecting light-induced photoreceptor cell death. L-SOP disrupts Müller glia proliferation subsequent to or in parallel with the activation of ascl1a and stat3 expression in the light-damaged retina. L-SOP inhibits cone cell regeneration in the light-damaged retina^[3].