Question: 

Voltage gated potassium (Kv) channels open upon cell depolarization. Conducting outward currents, they modulate action potential shape and frequency as well as cellular excitability. One member of the Kv channel family, Kv1.1, is a target of adenosine-to-inosine RNA editing. This editing leads to an amino acid exchange from isoleucine (I) to valine (V) in the middle of the pore forming S6 segment (I400V). Edited subunits (Kv1.1-I400V) were reported to have a reduced sensitivity to pore blocking agents including fatty acids. The present study analyzes the functional characteristics of I400V edited Kv1.1 channels.

Methods and Results: 

Electrophysiological recordings inXenopusoocytes and HeLa cells were conducted to quantify whole-cell currents of Kv1.1 and edited Kv1.1-I400V channels. Our experiments show that RNA edited Kv1.1-I400V channels generate whole-cell currents with a significantly reduced current amplitude, while the conductance-voltage relationship remained unchanged. Subsequent single channel patch-clamp recordings in transfected HEK293 cells revealed that Kv1.1 and edited Kv1.1-I400V channels have similar single channel properties, indicating that the reduced current amplitudes of edited channels should be caused by an altered trafficking of edited channels. A surface expression assay inXenopusoocytes revealed a 60% reduction in surface expression of edited Kv1.1-I400V subunits, while western blot analysis indicated that the total amount of channel protein was not altered by the I400V RNA editing.

Conclusion: 

While single channel electrophysiological properties and protein stability of edited channels are not affected, I400V edited Kv1.1 channels have a reduced whole cell current due to a reduction in surface expression.