Functional Characterization of the A414G Loss-of-Function Mutation in HCN4 Associated with Sinus Bradycardia

Patients carrying the heterozygous A414G mutation in HCN4 gene, which encodes protein, demonstrate moderate to severe bradycardia of heart. Tetramers subunits compose ion channels sinus node that carry hyperpolarization-activated ‘funny’ current (If), also named ‘pacemaker current’. If plays an essential modulating role pacemaker activity. To assess mechanism by results bradycardia, we first performed voltage clamp measurements on wild-type (WT) and mutant expressed Chinese hamster ovary (CHO) cells. These experiments were at physiological temperature using amphotericin-perforated patch-clamp technique. Next, applied experimentally observed mutation-induced changes CHO cells single human cell model developed Fabbri coworkers. The half-maximal activation V1/2 was 19.9 mV more negative than WT (p < 0.001). In addition, dependence (de)activation time constant showed a −11.9 shift 0.001) compared current. fully-activated density, slope factor curve, reversal potential not significantly affected mutation. computer model, cycle length substantially increased, almost entirely due steady-state activation, this increase prominent under vagal tone. introduction passive atrial load into further reduced beating rate, demonstrating even pronounced interactions between atria. conclusion, identified A414G-induced can explain clinically patients gene