Figure 5. Extracellular perfusion of 8-Br-cAMP mimics the action of internal cAMP.

Perfusion of the membrane permeable analogue of cAMP, 8-Br-cAMP (500 μm), produced a positive shift in the activation curve similar to that observed by including cAMP in the patch pipette (Fig. 4). In this example a positive shift of 9.3 mV is induced by 8-Br-cAMP; similar results were seen in 4 terminals. Overlaid data traces are shown on the right, with voltage protocols shown above. The activation curves measured from tail currents in this terminal are plotted on the right. Other changes, consistent with a shift in half-activation, were an increase in the holding current (I_hold), an increase in the instantaneous current (I_inst), and a slowing in tail current deactivation kinetics at -70 mV (*) as shown in the overlaid traces on the lower right.