CHARACTERIZATION OF A PLASMA-MEMBRANE ZINC TRANSPORTER IN RAT-BRAIN

Many studies now show that zinc plays a critical and unique role in ce ntral nervous system development and function. The cellular mechanisms of zinc afflux and influx are largely unknown and few models exist th at 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 (K-m = 15 mu M; V- max = 10 nmol/mg per 30 s), was seen in the absence of ATP, and was un affected 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 extravesi cular H+ concentration (pH = 5) resulted in near complete inhibition o f 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-revers ible transport of zinc across the plasma membrane of neurons. (C) 1998 Elsevier Science Ireland Ltd.