Figure 5.

Increases in Ca²⁺ current duration and ACh release produced by Ba²⁺ when K⁺ channels are not fully blocked. Ringer solution was Ca²⁺ current-ACh release Ringer. Prior to superfusion with Ba²⁺, nine control perineural currents (lower trace, a) were recorded. The mean amplitude of the perineural Ca²⁺ voltage change=0.64±0.03 mV (mean±1 s.d., n=9, range 0.59–0.69 mV). Simultaneously, nine control EPPs were recorded (a, upper trace). The mean EPP amplitude=4.5±0.2 mV, mean±1 s.d., n=9, range 4.1–4.9 mV). The coefficient of variation (s.d.mean⁻¹) was thus 0.5% for the perineural Ca²⁺ component and 0.6% for the EPPs, justifying (i) the use of the Rahamimoff (1967) statistical method to quantify the perineural recordings (see Methods) and (ii) the stability of both types of electrophysiological measurements in this solution. At (b), superfusion was begun with Ba²⁺ containing solution. Note the progressive prolongation of the perineural Ca²⁺ current (lower traces) and the increase in EPP amplitudes in Ba²⁺ to 7.2 mV (±1.0 mV) (mean±1 s.e.mean, n=6). Shortly after these records, EPPs were eliminated completely and both the Na²⁺ and Ca²⁺ components of the perineural traces were decreased (data not shown). Frequency of stimulation=0.05 Hz.