Figure 2. Photorelease of cAMP inhibits the slow AHP potassium conductance.

A, a depolarizing step to generate Ca²⁺ influx (arrowhead) is followed by Ca²⁺-dependent tail currents. The prominent slow component is the slow AHP current. Individual traces show I_sAHP (indicated) preceding (control), 5 s after photorelease of cAMP and 2.5 min after release of cAMP (recovery). B, time course of peak amplitude of I_sAHP shown in A. Photorelease of cAMP occurs at the flash (arrow). C, action of photoreleased cAMP on the persistent K⁺ current; cAMP release inhibits the tonically active outward current, holding potential −60 mV. D, I–V plots generated by a 3 s voltage ramp from −100 to −50 mV. K⁺ current inhibition (post flash trace) is associated with a decrease in conductance and shift in the zero current potential from −76 to −70 mV. E, time course of the experiment shown in C and D. Outward current develops as dibromo BAPTA diffuses from the pipette into the cell. Current inhibition and recovery follows the release of cAMP (flash).