Rapid changes in intracellular Zn2+ in rat hepatocytes

Abstract Changes in the concentration of free Zn 2+ were monitored in isolated rat hepatocytes using the fluorescent indicator zinquin (ethyl(2-methyl-8- p -toluenesulphonamido-6-quinolyloxy)acetate). The concentration of Zn 2+ in freshly isolated hepatocytes was 1.3 × 10 −6 M (range 0.61−2.7 × 10 −6 M). This value decreased by about 10%–15% during incubation in the absence of zinc and increased in a time- and concentration-dependent manner in the presence of exogenous zinc (K m ≈ 10 μM). IIb group metal ions led to a concentration-dependent increase in zinquin fluorescence. The rank of efficacy was Hg ≈ Cd > Pb (IVa) ⪢ Cu (Ib) ⋙ Ni (VIII). This rank resembles their ability to mobilize zinc from metallothioneins. 8-Br-3′,5′-cAMP (10 −4 M) caused a rapid decrease in Zn 2+ epifluorescence which was apparent within 10 min and was sustained throughout the experiment. This effect was gradually obliterated in the presence of external ZnCl 2 . The effect was specific for cAMP (or cAMP generating hormones) as the calcium-dependent hormone [arg 8 ]vasopressin (5 × 10 −8 M) did not affect intracellular Zn 2+ . An integrated role of zinc as a possible mediator in signal transduction is discussed.