Divalent ions released from stainless steel hypodermic needles reduce neuronal calcium currents

We have investigated the effects of saline solutions exposed to stainless steel hypodermic needles on their ability to reduce voltage-dependent calcium currents in chick dorsal root ganglion neurons and rat cerebellar Purkinje cells. Salines exposed to needles with brass hubs, but not those with plastic hubs, for as little as 2-3 sec reduced calcium currents in both cell types. The amplitude of the response was exposure-dependent and reversible. Elemental analysis of the exposed salines using inductively-coupled-plasma atomic emission spectroscopy revealed that Cu and Zn (but not Cd, Cr, Co, Fe, Mn, Ni or Pb) were released from the brazed needles. The amount of Cu plus Zn released in 30 sec was estimated to be 12-26 μM, depending upon the specific needle examined. Longer exposures produced proportionately higher concentrations of the metals. Dose-response curves for Cu or Zn ions applied directly to cells confirmed that similar concentrations of these ions reduced neuronal calcium currents. Our results indicate that divalent ions released from stainless steel hypodermic needles with brass hubs can interfere with measurements of calcium currents. In addition the results contribute new information regarding potential physiological and pathological actions of copper and zinc ions in biological tissues.