Figure 7.

$V_{\text{m}}^{\text{S}2}$s with non-parallel time courses at high field intensities

A, a cell (length:143 μm)that was successively stimulated with S2 stimuli of 38.3 and 56.2 V cm⁻¹. B, upper and lower sets of traces, show the $V_{\text{m}}^{\text{S}2}$ responses for the two S2 stimuli,which change from a parallel behaviour (at 38.3 V cm⁻¹) to non-parallel behaviour (at 56.2 V cm⁻¹). Moreover,following the pulse a depression in the plateau potential was observed for the S2 of 56.2 V cm⁻¹, indicated by the arrow in B, lower set of traces. For comparison with other cells the ${\hat{V}}_{\text{m}}^{\text{S}2}$s are indicated in parentheses. C, the S2 response measured at 1 ms ($V_{\text{m}}^{\text{S}2}$(n, 1.0)) and 9 ms ($V_{\text{m}}^{\text{S}2}$(n, 9.0)). The $V_{\text{m}}^{\text{S}2}$(n, 9.0) decreased in slope, and shifted in the depolarizing direction from $V_{\text{m}}^{\text{S}2}$(n, 1.0). D, the slope reduction Δ (∇$V_{\text{m}}^{\text{S}2}$), which is equivalent to the internal field E_i, rises exponentially during S2 (τ = 2.7 ms). E, the slope reduction at the end of S2, Δ(∇$V_{\text{m}}^{\text{S}2}$(n, 10)), increases monotonically with ${\hat{V}}_{\text{m}}^{\text{S}2}$ (r = 0.66, P < 0.05, n = 17).The dashed lines indicate that E_i is 3.2 V cm⁻¹ for a ${\hat{V}}_{\text{m}}^{\text{S}2}$ of 300 mV.