Fig. 11.

Pervanadate ionophoresis suppresses K⁺ currents in type B photoreceptors. A, top traces: family of transient (I_A) and delayed (I_Delayed) components of K⁺ current in a type B photoreceptor, elicited by depolarization to indicated membrane potentials (bottom), before ionophoresis of pervanadate ion. Bottom traces: currents recorded from the same cell 10 min after ionophoresis of pervanadate ion. Pervanadate suppressed both I_A and I_Delayed at all potentials tested. B: pervanadate's inhibition of K⁺ currents was blocked by 100 μM genistein. K⁺ currents before (top traces) and 10 min after (bottom) pervanadate ionophoresis in the presence of genistein. C: summary data for suppression of K⁺ currents resulting from pervanadate ionophoresis (n = 7) or pervanadate ionophoresis in the presence of genistein (n = 3). Pervanadate ionophoresis suppressed the K⁺ currents, but not if genistein was present in the bath. Currents measured at 0 mV. D: summary data depicting the effects of pervanadate (n = 7) or the combination of pervanadate and genistein (n = 3) on K⁺ currents, at all voltages, measured about 10–12 min after ionophoresis of pervanadate. Both the transient (I_A) and sustained (I_Delayed) components of K⁺ current were decreased by pervanadate (top), although genistein blocked the suppressive effects of pervanadate on both components of K⁺ current (bottom).