Figure 1.

(a) Amperometric detection of secretion evoked in control (left traces) and chronically hypoxic (right) PC12 cells in response to 50 mM K⁺ (stimulus application began 10 s before beginning of traces). For the periods indicated by horizontal bars, cells were exposed to either Ca²⁺-free perfusate (upper traces), or to 200 μM Cd²⁺ (lower traces) in the presence of 2.5 mM Ca²⁺ (also in the continued presence of 50 mM K⁺) as indicated. Note that in chronically hypoxic cells, 200 μM Cd²⁺ failed to inhibit secretion completely. (b) Bar graph showing mean (+s.e.m. bars) exocytotic frequency recorded in cells previously exposed to 10% O₂ for 21–26 h, in response 50 mM K⁺ in the presence of 200 μM Cd²⁺ alone (open bar), or following further blockade with Zn²⁺(10 mM), La³⁺(1 mM) Congo Red (10 mM) or 3D6 antibody (5 μg ml⁻¹) as indicated. All blockers produced significant inhibition (p<0.04–0.001) of Cd²⁺-resistant release (n=8–12 recordings in each case).