Fig. 8.

Genistein increases K⁺ currents of type B photoreceptors. A, top traces: currents elicited by depolarization of a voltage-clamped type B photoreceptor to indicated membrane potentials (see bottom right), just prior to genistein exposure. Bottom traces: currents from the same cell recorded 15 min following exposure to genistein. Both the transient and sustained components of K⁺ current were increased. B: summary data depicting genistein's enhancement of the transient K⁺ current (I_A), at 0 mV, for 5 cells measured 15 min after bath application. The sustained K⁺ current (I_Delayed *) was also significantly enhanced after the results of one anomalous cell were omitted. Enhancement is expressed as a percentage of the original baseline (pregenistein) value. C: time course of genistein's enhancement of K⁺ currents. Genistein's effects were apparent within a few minutes of application, peaked at about 5 min for I_A and slowly declined thereafter. I_Delayed continued to increase over the next 10 min. D–G: summary I–V relationships for I_A and I_Delayed, before and after exposure of cells (n = 4) to genistein. Genistein increased the voltage dependence of both the A current (D, F) and I_Delayed (E, G). In the absence of genistein, I_A and I_Delayed both showed e-fold increases in amplitude per about 14 mV (from −15 to +10 mV). Genistein enhancement of I_A and I_Delayed was accompanied by an average 19% increase in the voltage dependence of I_A and a 30% increase in voltage dependence for I_Delayed. These changes are most apparent in the slopes of semi-log (log–linear [log–lin]) plots in F and G (indicated by the linear regression lines and associated equations). H: genistein increases the rate of inactivation of I_A. Examples shown are of single-exponential fits of current records of I_A inactivation (at +10 mV), before (left) and 10 min after (right) genistein exposure. Genistein increased I_A inactivation by roughly 26%. Current traces have been scaled to the same level.