FIGURE 2.

Estimates of capacitive change and conservation of charge in oocytes. (A) Raw, unsubtracted traces of the onset current in response to a 160 mV voltage pulse from −70 mV. The dotted trace shows the transient current response under baseline conditions (absence of drug). The solid trace shows the current response in the presence of 50 μM 3β5αPS. (B) Replot of the dotted trace (absence of steroid) from A showing a single exponential fit (solid line) superimposed on the relaxation of the transient, extrapolated to the onset of the voltage pulse to +90 mV. The shading under the fit represents the integral used to calculate total charge displaced. The inset shows the estimate of cell capacitance (total charge displaced, normalized to the amplitude of the voltage pulse) in the absence (black bar) and presence (white bar) of 3β5αPS. *p < 0.05, paired t-test, n = 11 oocytes. (C and D) The traces are superimposed subtractions (50 μM 3β5αPS minus baseline saline) showing the transient response to pulse onset (solid line) to +90 mV and offset (dotted line) on return to −70 mV. The offset responses have been inverted and superimposed for comparison with the onset responses. For long voltage pulses the charge observed on step back to −70 mV was larger than the charge at onset, but for short pulses charge was nearly completely conserved.