Use-Dependent Removal of the 4-Aminopyridine-Induced Block of the Transient K⁺ Current in Rat Dorsal Root Ganglia

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Effects of 4-aminopyridine (4-AP) on the transient K⁺ current (I_A) was studied in rat sensory neurons using the whole cell patch-clamp technique. The amplitude of I_A was reduced by 4-AP. The steady-state inactivation curve for I_A was shifted in the positive direction by 4-AP, suggesting that the blocking action of 4-AP may be attenuated by membrane depolarization. When two I_As were evoked with variable intervals, the peak amplitude of the I_A induced by the second pulse was augmented in the presence of 4-AP. These results indicate that the action of 4-AP can be modulated by concurrent neuronal activities.