Fig. 3.
Properties of Ih in afferent dendrites. A and B: Ih currents in response to voltage steps (every 10 s for 3 s, from a holding potential of −64 mV to voltages between −144 and −54 mV in 10 mV increments; see inset). External solution with: TTX (1–2 μM), 4-aminopyridine (4-AP, 2 mM), tetraethylammonium (TEA, 10–30 mM), and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 μM). A: in control solution. B: with 200 μM cyclic adenosine monophosphate (cAMP) intracellularly and additionally 200 μM 8-bromoadenosine-3′,5′ cyclic monophosphate (8-Br-cAMP) extracellularly. C: I–V relations in control (n = 3, black) and with cAMP analogs (n = 4, red). D: voltage dependence of Ih measured from tail currents. Tail current amplitudes were normalized and fit with a Boltzmann equation. Vhalf and slope factors were −104 ± 3 mV, 11 ± 1 in control (n = 3, black), and −91 ± 2 mV, 11 ± 1 in cAMP analogs (n = 4, red). E: activation kinetics of Ih currents. Current responses to voltage steps from −134 to −104 mV were fit with 2 exponentials, providing 2 time constants (τfast, τslow). Both time constants were significantly faster for currents recorded with cAMP analogs (n = 4, red) compared with control (n = 3, black). F: reversal potential of Ih. Conditioning voltages were applied for 3 s (to −124, −104, or −84 mV), followed by 10 ms voltage ramps (from −144 to −74 mV) (top traces: voltage commands; bottom traces: current responses to the commanding voltage ramps). The reversal potential was −45.5 mV for this recording.