Fig. 4:

The role of I_h in autonomous pacemaking. a. Recording from IO neuron showing a role for I_h in pacemaking, reproduced from Bal and McCormick 1997.²²⁵ b. Schematic showing noradrenergic signaling through β₂-receptors leading to an increase in cAMP. c. Channel opening probability as a function of voltage. Note that in the presence of cAMP (in blue) the curve depolarizes so that more channels are open at a given voltage while less cAMP (in red) has the opposite effect. d. The effect of cAMP on the cardiac action potential in a sinoatrial node cell. cAMP mediated agonization of HCN channels increases the firing rate. Color scheme adopted in panel c corresponds to the conditions in panel d. Panels b-d based on Fig. 4 from DiFrancesco and Borer 2008,²¹⁵ reprinted with modifications and permission from Springer.