PKG inhibitor is a specific cGMP-dependent PKG inhibitor (Ki = 86 μM). This synthetic peptide is a nonphosphorylatable analog of a substrate corresponding to the serine-32 phosphorylation site in histone H2B. PKG inhibitor has been reported to block cGMP-dependent NMDA potentiation and nitric oxide-induced depression of GABA currents in cultured retinal amacrine cells.