Figure 10. La³⁺ profoundly modifies intra-membrane charge movement.

A, charge movement currents recorded using an external solution lacking Cd²⁺ and Co²⁺ exhibit a temporally delayed component and similar current kinetics to fibres bathed in our standard control solution. Ca²⁺ was reduced to 0.5 mm and 10 mm Mg²⁺ was added to the external solution to block inward ionic components. B, fibres bathed in control external solution (open circles, dashed line) demonstrate a very similar Q vs. V relationship to fibres bathed in Cd²⁺ and Co²⁺ free external solution (filled circles, continuous line). C, charge movement currents recorded using an external solution supplemented with 0.3 mm La³⁺ exhibit rapid current kinetics and no clear temporally delayed ‘hump’ component. D, fibres bathed in our control external solution supplemented with La³⁺ demonstrate decreased maximal charge moved and a rightward shift in the voltage dependence of charge movement when compared to fibres bathed in our standard external solution. E, charge movement currents recorded in control and La³⁺-treated fibres in response to depolarizing pulses to −10 mV of increasing duration (2 ms increments) to evaluate charge movement conservation. F, Q_ON or Q_OFFvs. pulse duration for the complete set of pulses of corresponding traces illustrated in E. The normalized charge–pulse duration relationships for both Q_ON and Q_OFF are fitted to single exponential functions (continuous lines). The calculated time constant for charge development in the Cd²⁺/Co²⁺ exposed fibre was 13 ms, compared to 2.4 ms for the fibre exposed to La³⁺.