Figure 3. Nanomolar concentrations of α-LT induce Ca²⁺-dependent exocytosis.

A, application of 10 nm α-LT, by puffer pipette, in the vicinity of a human islet cell bathed in 2 mm Ca²⁺ PSS produces a barrage of discrete spikes in the amperometric current trace I_amp. This response is distinct from the ‘dome + spike’ pattern produced by a subsequent brief ‘poke’ of the cell with a carbon fibre electrode. B, in contrast shows that 10 nm α-LT applied by puffer pipette in the vicinity of a human islet cell bathed in no added Ca²⁺/EGTA PSS produces no spikes in I_amp, until Ca²⁺ is later added to the bath via close-range application of 10 mm Ca²⁺ PSS from a second puffer pipette. C and D, display, for identical experiments of the types illustrated in A and B, respectively, the cumulative total amperometric spike events (ΣAS) versus time after addition of α-LT. C, in some experiments 50 μm nifedipine (○)?was added to block endogenous voltage-dependent Ca²⁺ channels.