KCl-induced CREB phosphorylation is blocked by MK-801. In the absence of phosphoCREB antiserum, no quantitative difference in CREB binding to the CaRE site is observed (Control). The phosphoCREB antiserum interacts with part of the bound complex (creating the supershifted band, seearrow) in experiments performed 15 min after stimulation with dopamine (50 μm) or KCl (25 mm). Pretreatment of cultures for 30 min with MK-801 (50 μm) prevents phosphorylation of CREB in both paradigms, as demonstrated by the lack of a supershifted band in the respective lanes; n = 6.