Functional expression of a GFP-tagged Kv1.5 alpha-subunit in mouse ventricle

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Ion Channel Biology

Background:

• Voltage-gated ion channels are crucial for cardiac electrical activity.
• Understanding ion channel expression and function is key to treating heart conditions.
• Kv1.5 channels contribute to the slow delayed rectifier potassium current (I(K,slow)) in the heart.

Purpose of the Study:

• To assess the feasibility of increasing cell surface expression of voltage-gated ion channels in cardiac cells in vivo.
• To investigate the functional consequences of ectopic Kv1.5 channel expression in the heart.
• To characterize the properties of the overexpressed Kv1.5-GFP current.

Main Methods:

• Generation of transgenic mice expressing Kv1.5-GFP under the alpha-MHC promoter.
• Heterogeneous expression of Kv1.5-GFP in ventricular myocytes was observed.
• Electrophysiological recordings (voltage-clamp) and pharmacological analysis using 4-aminopyridine (4-AP) were performed.

Main Results:

• Kv1.5-GFP expression led to decreased action potential durations in positive cells.
• Peak outward potassium currents were significantly higher in GFP-positive ventricular myocytes.
• A selective increase in a 4-AP-sensitive current was observed, with slower inactivation kinetics compared to endogenous I(K,slow).

Conclusions:

• Ectopic expression of Kv1.5-GFP in cardiac myocytes is feasible in vivo.
• Overexpression alters action potential duration and potassium current properties.
• Differences in inactivation kinetics suggest altered interactions with accessory subunits or posttranslational modifications.