Fig. 4

Figure 4. Sinoatrial node (SAN) enhancer activity co-localizes with Hcn4 expression and functional cardiac pacemaker cells.A and A?, Whole-mount fluorescence imaging of ISE-mCherry/Hcn4 (hyperpolarization-activated cyclic nucleotide-gated ion channel 4)?green fluorescent protein (GFP) embryos at embryonic day (E) 8.5 (arrows denote inflow tract), (B and B?) E10.5, and (C and C?) E14.5 imaged for mCherry alone (top row) and mCherry/GFP merge (bottom row). *mCherry+/GFP- SAN extension into the right atrium (ra). D, Postnatal ISE-mCherry activity at P2 and (E) in adult isolated pacemaker cells (PCs) with typical PC morphology. F, Spontaneous action potentials (APs) recorded from an adult mCherry+ isolated pacemaker cell. G, Firing rate, maximum diastolic potential, AP amplitude, early diastolic depolarization rate (EDDR), upstroke velocity (dV/dt max), and AP duration (APD) at 50% and 90% repolarization in 12 isolated adult mCherry+ pacemaker cells. Error bars indicate SD. H, Whole-cell voltage-clamp on an mCherry+ adult cell with funny current (I(f)) elicited by a series of hyperpolarizing voltage pulses from a holding potential of -40 mV to -130 mV in 10 mV increments. I, Mean I(f) current density at the indicated voltages in 11 mCherry+ PCs. Error bars indicate SEM. la indicates left atrium; and sv, sinus venosus.