There must be some channels that keeps this very stable. It seems to be that the resting membrane potential of pacemaker cells is steadily increasing until the threshold voltage. I think the same must apply to the cardiomyocyte. However, many times I see schematic figures where the resting membrane potential of pacemaker cell is drawn steadily increasing, in contrast to cardiomyocyte. Why?
Is there some evidence for that difference in Phase 4 between cardiomyocyte and Pacemarker cell? I think both should be increasing steadily.
Pacemaker action potential
and cardiomyocyte action potential