Figure 6. Effects of TEA on the cAP and [Ca²⁺]_pre,t.

Sample traces of cAPs and [Ca²⁺]_pre,t under control conditions and in the presence of 10 mM TEA. A, in contrast to application of 4-AP, TEA did not evoke a progressive increase in the amplitude of VSD signals. No difference was detected in the waveform of the FV among stimuli within the test train. The inset shows superimposed presynaptic FVs. TEA not only increased the duration but also reduced the amplitude of the FV compared with control, suggesting a decreased excitability of fibres in the presence of high concentrations of TEA. B, [Ca²⁺]_pre,t in control and in the presence of 10 mM TEA. Consistent with the observed cAP, there was much less facilitation of the [Ca²⁺]_pre,t for subsequent stimuli within the test train. C, summary data for the [Ca²⁺]_pre,t in the presence of TEA. On average, 10 mM TEA increased the [Ca²⁺]_pre,t to 156 ± 3, 168 ± 7, 171 ± 5 and 174 ± 4 % of control (n = 4) for successive stimuli within the test train. The amount of [Ca²⁺]_pre,t induced by 10 mM TEA is probably an underestimate, due to the reduced amount of fibres activated. There was no significant facilitation of [Ca²⁺]_pre,t as compared with application of 4-AP.