The role of intracellular Zn
2+ in the translocation of protein kinase C from cytosol to membrane fractions was examined by the [
3H]phorbol 12,13-dibutyrate (PDBu) binding method in guinea pig cerebral synaptoneurosomes.
N-methyl-d-aspartate (NMDA, 100 μM) and calcium ionophore A23187 (0.3–30 μM) decreased the binding activity in the cytosol with a concomitant increase in the membrane fractions. Pretreatment of synaptoneurosomes with a heavy metal chelator,
N,N,N′,
N′-tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN), inhibited the NMDA- and A23187-induced changes of the distribution of [
3H]PDBu binding sites in cytosol and membrane fractions. The inhibitory effect of TPEN was negated by a preincubation of TPEN with equimolar Zn
2+ but not by that with Ca
2+. The addition of 500 μM Zn
2+ to the lysate of synaptoneurosomes induced an increase of [
3H]PDBu binding activity in the membrane fraction with a concomitant decrease in the cytosol fraction, as did 100 μM Ca
2+. Low concentrations of Zn
2+ (10 μM), which alone had no effect on the distribution of the binding, significantly enhanced the effect of 10 μM Ca
2+ in the lysate. Under those conditions TPEN inhibited the Zn
2+-potentiated Ca
2+-dependent changes in the binding. These results suggest that intracellular Zn
2+ is essential for the agonist-induced translocation of protein kinase C in guinea pig synaptoneurosomes.
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