Decreased phorbol ester binding in the parahippocampal gyrus from subjects with schizophrenia is not associated with changes in protein kinase C

Combining in situ radioligand binding with autoradiography, we previously identified a reduction of [³H]phorbol 12, 13-dibutyrate binding in the parahippocampal gyrus from schizophrenic subjects. To determine whether these changes were due to decreases in the level of protein kinase C, we measured [³H]phorbol 12, 13-dibutyrate binding, levels of the protein kinase C isoforms α, β, δ, ε, γ, η and θ, as well as protein kinase C activity in crude particulate membranes from parahippocampal gyri of 15 schizophrenic and 15 control subjects. There was a significant decrease in the density (mean ± SEM: 6.56 ± 0.73 pmol mg^-1 vs 9.68 ± 1.22 pmol mg^-1; P < 0.05) and affinity (mean K_D ± SEM: 4.64 ± 0.34 nM vs 2.95 ± 0.35 nM; P < 0.005) of [³H]phorbol 12, 13-dibutyrate binding in homogenates from schizophrenic subjects. There were no significant changes in levels of the protein kinase C isoforms which are known to bind phorbol esters or in the activity of protein kinase C in membranes from schizophrenic subjects. These results suggest that there are changes in molecules capable of binding [³H]phorbol 12, 13-dibutyrate, other than protein kinase C, in the parahippocampal gyrus from subjects with schizophrenia.