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 −4M) 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.
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