Characterization of a plasma membrane zinc transporter in rat brain

Many studies now show that zinc plays a critical and unique role in central nervous system development and function. The cellular mechanisms of zinc efflux and influx are largely unknown and few models exist that describe cellular zinc transport in the brain. This report provides convincing evidence of a zinc transporter in plasma membrane vesicles isolated from rat brain. Zinc uptake was saturable (Km = 15 microM; Vmax = 10 nmol/mg per 30 s), was seen in the absence of ATP, and was unaffected by gradients for other ions such as Na+ or K+. Increasing the ionic strength of the extravesicular media with Na+, K+, or choline+ reduced zinc uptake approximately 50%. Whereas, increasing extravesicular H+ concentration (pH = 5) resulted in near complete inhibition of zinc uptake. Intravesicular zinc was rapidly released upon lowering extravesicular concentrations of zinc with the heavy metal chelator O-phenanthroline (1 mM). The results are consistent with a freely-reversible transport of zinc across the plasma membrane of neurons.