Kinetics of cation uptake in Xenopus laevis oocytes. A, top, Cd uptake as a function of time in ZIP8 cRNA-injected versus water-injected oocytes. *P <0.01. **P <0.001. At bottom, Cd uptake as a function of its concentration in ZIP8 cRNA-injected minus water-injected oocytes; incubation time was 60 min. B, top, Zn uptake in ZIP cRNA-injected versus water-injected oocytes. *P <0.05. **P <0.01. At bottom, Zn uptake, determined as described in part A. Circles and brackets at top denote means ± S.E. Vmax and Km values are expressed as means ± S.E. Circles and brackets at bottom denote means ± S.D.