Kir2 inward rectification-controlled precise and dynamic balances between Kir2 and HCN currents initiate pacemaking...

Area of Science:

• Cardiology
• Cellular Electrophysiology
• Molecular Biology

Background:

• Spontaneous rhythmic action potentials in pacemaker cells drive essential physiological processes like heartbeat.
• The precise molecular mechanisms governing the initiation of pacemaking activity remain incompletely understood.
• Understanding pacemaking origins is crucial for developing therapies for cardiac arrhythmias.

Purpose of the Study:

• To elucidate the ion channel mechanisms responsible for initiating spontaneous rhythmic action potentials.
• To engineer a cellular model exhibiting controllable pacemaking activity.
• To investigate the roles of specific potassium and cation channels in generating rhythmic electrical activity.

Main Methods:

• Heterologous expression of inward rectifier K+ subfamily 2 isoform 1 (Kir2.1) and hyperpolarization-activated cyclic nucleotide-gated isoform 2 (HCN2) channels in human embryonic kidney (HEK) 293 cells.
• Co-expression with voltage-gated Na+ (Na_v1.5) or Ca2+ (Ca_v3.1) channels to trigger action potentials.
• Analysis of membrane potential oscillations and action potential generation under varying channel expression levels.

Main Results:

• Engineered HEK293 cells demonstrated spontaneous rhythmic membrane potential oscillations between -64 and -34 mV.
• Dynamic interplay between Kir2.1 and HCN2 currents was essential for generating rhythmic activity.
• Action potentials were triggered upon reaching threshold potential, resulting in pacemaking at rates up to 67 beats/min.
• Kir2.1-like inward rectification was critical; cells lacking this property did not exhibit pacemaking.

Conclusions:

• Precise and dynamic balances between Kir2.1 and HCN channel currents initiate spontaneous rhythmic action potentials.
• Kir2.1 inward rectification plays a fundamental role in establishing the origin of pacemaking activity.
• Kir2 and HCN channels are essential components for generating pacemaking.