ZINC STATUS AND DISTRIBUTION OF PROTEIN-KINASE-C IN RAT PLATELETS

Platelet aggregation is impaired by zinc deficiency and in vitro zinc has been reported to affect subcellular distribution of protein kinase C (PKC), an enzyme required for platelet aggregation. In this study, the effects of zinc deprivation and in vitro calcium on phorbol ester- induced platelet aggregation and PKC distribution were investigated. P latelets were collected from rats fed a low zinc diet (<1 mg/kg) and c ontrols that consumed a zinc adequate diet (100 mg/kg), ad libitum or pair-fed. Washed platelets were stimulated with phorbol myristate acet ate (PMA, 160 nmol/L) and the rate of aggregation determined. Without added Ca2+ the rate of aggregation was not affected by zinc status. wi th added Ca2+ (1 nmol/L) the rate was decreased by zinc deficiency (P < 0.05). For PKC measurement, platelets from each animal were pretreat ed briefly with either 0 or 1 mmol/L Ca2+, then suspended in a low Ca2 + buffer, and sonicated. Specific binding of phorbol dibutyrate (PDBu) to mixed membranes and cytosol was measured. Pretreatment with Ca2+ i ncreased binding to membranes and decreased binding to cytosol. Overal l, zinc deficiency decreased [H-3]PDBu binding to membranes approximat ely 10% (P = 0.01), but had no effect on cytosol binding. Only in the presence of in vitro Ca2+ did zinc deficiency decrease both PMA-induce d aggregation and phorbol ester binding to mixed membranes. Zinc statu s had no effect on the distribution of phorbol ester binding, suggesti ng that low zinc status decreased availability of extracellular calciu m and thus decreased membrane PKC binding affinity or the stability of PKC in the membranes.