Binding of 63Ni (II) to ultrafiltrable constituents of rabbit serum in vivo and in vitro.

Binding of 63Ni(ll) to ultrafiltrable constituents of rabbit serum was studied (a) after in vitro incubation (2 h, 37 degrees C) of rabbit serum with 63NiCl2 (10-100 mumol/liter), and (b) at intervals (0.25-2 h) after in vivo administration of 63NiCl2(40-160 mumol/kg body wt,i.v.). Serum ultrafiltrates were fractionated by thin-layer chromatography, and the separated compounds made visible by autoradiography and by ninhydrin staining. Severel (congruent to 5) ultrafilitrable 63Ni-complexes were demonstrable as distinct radiodense 63Ni-bands with chromatographic mobilities corresponding to those of ninhydrin-positive bands. Unbound 63Ni(ll) was not detected in serum ultraviltrates in either the in vitro or in vivo experiments. In sera (n equals 10) incubated in vitro with 63Ni(ll) (10 mumol/liter), the mean percentage of ultrafiltrable 63Ni was 36% (range equals 33-38) of total serum 63Ni. In contrast, in sera (n equals 10) obtained 2 h after i.v. injection of 63Ni(ii) (40 mumol/kg), the mean concentration of total serum 63Ni was 10.8 mumol/kg), the mean concentration of total serum 63Ni was 10.8 mumol/liter (ranger equals 6-14), and the mean percentage of ultrafiltrable 63Ni was 15% (range equals 9-21) of total serum 63Ni. The disparity between the percentages of ultrafiltrable 63Ni obtained in vitro and in vivo was obviated when the in vivo experiments were performed in rabbits bilaterally nephrectomized, with ligated common bile ducts. This investigation confirms the existence of several nickel receptors in serum ultrafilitrates and substantiates the role of ultrafiltrable complexes in the excretion of nickel.