Low zinc status in rats impairs calcium uptake and aggregation of platelets stimulated by fluoride

Platelets from rats of low zinc status exhibit impaired aggregation in response to ADP stimulation. The abnormality has been traced to defective uptake of calcium from the external medium. This study was designed to determine the location of the molecular defect and whether or not the ADP receptor is involved. Washed platelets were collected from rats fed a low zinc diet (< 1 mg/kg) and control groups that consumed a zinc-adequate diet (100 mg/kg), ad libitum- and pair-fed. Fluoride, a G-protein stimulant, was used to bypass the ADP receptor. F- stimulated platelet aggregation and calcium uptake; both of these functions were impaired by zinc deficiency. At 10 mM F-, the time to half maximal aggregation was increased from 1.8 min in platelets from control to 2.8 min in zinc deficient rats. At 8 mM F-, the uptake of calcium was decreased from 170 to 85 nM cytosolic free calcium. At this concentration of F- there was no release of internal calcium. The results show that the molecular defect in the zinc-deficient platelet is located in the aggregation pathway beyond the ADP receptor and suggest a point between, or including, a G-protein and the plasma membrane calcium channel.