17-β-estradiol rapidly reduces K^<b>+</b> currents in MPN neurons.

<p>A, K⁺ currents evoked by a voltage step from −74 mV to +36 mV, in control solution, after the addition of 10 µM 17-β-estradiol and after wash-out of 17-β-estradiol, as indicated. B, time course of estradiol-induced depression, from the neuron in A. Mean current 190–200 ms after voltage steps to +26 mV from −74 mV. (No leak current subtraction.) 17-β-estradiol was applied as indicated. Superimposed lines show fitted exponentials. C, concentration-response relation for 17-β-estradiol-induced depression of K⁺ currents. Mean currents 590–600 ms after a voltage step to +26 mV from −74 mV. Smooth line is described by Equation 1 with EC₅₀ = 9.7 µM, n = 1.2, <i>Inh</i>_max = 58%. Data from 7 neurons. D, I–V relations for mean current 590–600 ms after a voltage step from −74 mV to the potentials indicated, for one MPN neuron. Current in solutions as indicated. E, relation between the effect of 10 µM 17-β-estradiol (ratio of current in estradiol to that in control solution; mean current 590–600 ms after voltage step from −74 mV) and membrane voltage for 12–13 neurons. Mean±S.E.M. The superimposed line is an exponential function, with <i>e</i>-fold change per 14 mV, fitted to the data. F–G, Ca²⁺ independence of estradiol-sensitive current. F, currents evoked by a voltage step from −74 mV to +6 mV, with extracellular solution modified as indicated. Note that estradiol (10 µM) induced a similar depression in the presence and absence of Ca²⁺. G, current depressed (mean current 590–600 ms after a voltage step to +6 mV) by 10 µM 17-β-estradiol added to standard extracellular solution (left bar) and to a solution with Co²⁺ substituted for Ca²⁺ (right bar). The same 9 neurons were used for both conditions. The difference was not significant.</p

Model of estradiol action on voltage-gated K^<b>+</b> currents.

<p>A, state diagram showing the model with estradiol (E) binding to open channels (O) to form the blocked state with estradiol bound (BE). Dashed box includes the voltage-dependent transitions between closed states (C1 and C2) and the open state. B, experimentally obtained raw data currents from one neuron in control conditions (<i>black curves</i>) and in the presence of 10 µM 17-β-estradiol (<i>grey curves</i>), for comparison with C. The currents were activated by voltage steps (600 ms) to indicated potentials from a holding potential of −74 mV. C, computed K⁺ currents for control conditions (corresponding to states enclosed by dashed box in A; <i>black curves</i>), and for the presence of 10 µM 17-β-estradiol according to the model (<i>grey curves</i>). Voltage steps as in B. D, computed currents at different concentrations of 17-β-estradiol, as indicated. Voltage step to +26 mV from −74 mV. E, concentration-response curve for computed currents 600 ms after a voltage step from −74 mV to +26 mV. EC₅₀ value and Hill coefficient (<i>n</i>) are given in the figure. F, voltage dependence of the block induced by 10 µM 17-β-estradiol (600 ms after a voltage step from −74 mV to indicated potentials) according to the model. The current in 17-β-estradiol is plotted relative to control. The line is a fitted exponential curve, with an <i>e</i>-fold change in relative current per 15 mV.</p

Blocking effects of different steroids on K^<b>+</b> currents and lack of effect of ICI 182,780.

<p>All steroids were applied at a concentration of 10 µM and the estrogen-receptor blocker ICI 182,780 at a concentration of 50 µM. Currents were measured 590–600 ms after voltage steps from −74 mV to +6 mV. A–D, effects of the indicated substances at repetitive voltage steps given to individual neurons. E, summary of blocking effects plotted relative to the blocking effect of 10 µM 17-β-estradiol observed in the same neurons. The number of cells studied for each condition is given within parenthesis. The negative value for estrogen sulphate indicates that this substance caused a slight potentiation of the K⁺ currents.</p

Inactivation of K⁺ currents.

<p>A, K⁺ currents evoked by >60 s long voltage steps from −74 mV to +16 mV, in control solution (<i>upper trace</i>) and in 10 µM 17-β-estradiol (<i>lower trace</i>). Note the slow, but large inactivation in control solution as well as in estradiol. B, voltage dependence of steady-state inactivation. Peak current at +26 mV plotted <i>versus</i> the voltage of a 60 s long preceding interval. Control solution (<i>squares</i>) and 10 µM 17-β-estradiol (<i>circles</i>). Smooth lines are fitted Boltzmann relations (Equation 2) with voltage for half-maximal inactivation (U_½) and slope factor (U_S) indicated. A steady non-inactivating current component was subtracted. C, relative recovery from inactivation caused by a 16-s interval at +26 mV (ending at time 0): Superimposed curves represent the currents at +26 mV after varying recovery intervals at −74 mV with and without 17-β-estradiol, as indicated. D, relative recovery for peak currents as in C plotted <i>versus</i> the recovery interval at −74 mV. Smooth line is described by a monoexponential function with time constant 0.81 s. The differences between curves for control and estradiol are within the range of trial-to-trial variability for a single condition in these long-duration experiments.</p

Effects of altered [K^<b>+</b>]_o on block by 17-β-estradiol.

<p>A, currents recorded at 600-ms voltage steps to −24 mV from −74 mV. At −24 mV currents in standard [K⁺]_o of 5 mM are outward (<i>top traces, control black</i>) with some reduction caused by 10 µM 17-β-estradiol (<i>grey</i>). With a [K⁺]_o of 140 mM, currents (<i>lower traces, control black</i>) are inward and 10 µM 17-β-estradiol (<i>grey</i>) also reduces the current. B, relative current (mean±S.E.M. from 6 cells) in 10 µM 17-β-estradiol, measured 590–600 ms after a voltage step as in A. C, currents as in A but with voltage step to +16 mV. D, relative current (mean±S.E.M. from 5 cells) in 10 µM 17-β-estradiol, measured 590–600 ms after a voltage step as in C. E, currents recorded as in C, but with comparison between standard [K⁺]_o of 5 mM and [K⁺]_o = 0 mM. F, relative current (mean±S.E.M. from 7 cells) in 10 µM 17-β-estradiol, measured 590–600 ms after a voltage step as in E. Note the slight, but significant difference in blocking effect recorded from the same cells when [K⁺]_o = 5 mM and when [K⁺]_o = 0 mM.</p

Sensitivity to blockers and concentration-dependent rate of current decline.

<p>A, currents (averages of 10 traces) evoked by a voltage step from −74 mV to +6 mV in solutions as indicated. Note that 30 mM TEA blocked a major fraction of the voltage-activated K⁺ current without leaving any significant transient current remaining. Note also that the blocking effects of TEA and 17-β-estradiol were overlapping. B, currents evoked by voltage steps from −74mV to +26 mV, in control solution and in the indicated concentrations of 17-β-estradiol. Note the faster current decline and the larger block with increasing concentration of 17-β-estradiol. C, ratio of current (<i>grey</i>) in 17-β-estradiol to that in control solution, to show the time course of current inhibition. The traces were well fitted by exponential functions with time constants 134ms (<i>top</i>), 75ms (<i>middle</i>) and 49 ms (<i>bottom</i>), shown as superimposed black lines. Computed from the traces shown in B. D, dependence of time constant of relative current, as in C, on concentration of 17-β-estradiol. Mean±S.E.M. for the number of neurons indicated. Voltage steps to +26mV from −74 mV. E-F, overlapping block by estradiol and r-stromatoxin-1. E, time-course of block of the K⁺ current (mean current 590–600 ms after a voltage step from −74 to +26 mV) by estradiol, r-stromatoxin-1 and a combination of these substances, as indicated. F, K⁺ currents (averages of 10 traces) evoked by voltage steps from −74 to +26 mV. Concentration of blockers as in E. Note the lack of effect of estradiol in the presence of r-stromatoxin-1. Data in E and F from the same neuron.</p