Molecular dissection of the inward rectifier potassium current (IK1) in rabbit cardiomyocytes: evidence for heteromeric co-assembly of Kir2.1 and Kir2.2

• Published in: The Journal of physiology 2003-07, Vol.550 (2), p.365-372
• Main Authors: Zobel, Carsten, Cho, Hee Cheol, Nguyen, The‐Tin, Pekhletski, Roman, Diaz, Roberto J., Wilson, Gregory J., Backx, Peter H.
• Format: Article
• Language: English
• Subjects: Adenoviridae - genetics; Animals; Cell Line; Electric Stimulation; Electrophysiology; Heart Ventricles - cytology; Heart Ventricles - metabolism; Heterozygote; Immunoblotting; Membrane Potentials - physiology; Mutagenesis, Site-Directed - genetics; Mutation - genetics; Myocytes, Cardiac - metabolism; Original; Patch-Clamp Techniques; Potassium Channels, Inwardly Rectifying - biosynthesis; Potassium Channels, Inwardly Rectifying - genetics; Rabbits
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2002.036400

Cardiac inward rectifier K + currents ( I K1 ) play an important role in maintaining resting membrane potential and contribute to late phase repolarization. Members of the K ir2.x channel family appear to encode for I K1 . The purpose of this study was to determine the molecular composition of cardiac I K1 in rabbit ventricle. Western blots revealed that K ir2.1 and K ir2.2 , but not K ir2.3 , are expressed in rabbit ventricle. Culturing rabbit myocytes resulted in a ∼50% reduction of I K1 density after 48 or 72 h in culture which was associated with an 80% reduction in K ir2.1 , but no change in K ir2.2 , protein expression. Dominant-negative (DN) constructs of K ir2.1 , K ir2.2 and K ir2.3 were generated and tested in tsA201 cells. Adenovirus-mediated over-expression of K ir2.1dn , K ir2.2dn or K ir2.1dn plus K ir2.2dn in cultured rabbit ventricular myocytes reduced I K1 density equally by 70% 72 h post-infection, while AdK ir2.3dn had no effect, compared to green fluorescent protein (GFP)-infected myocytes. Previous studies indicate that the [Ba 2+ ] required for half-maximum block (IC 50 ) differs significantly between K ir2.1 , K ir2.2 and K ir2.3 channels. The dependence of I K1 on [Ba 2+ ] revealed a single binding isotherm which did not change with time in culture. The IC 50 for block of I K1 was also unaffected by expression of the different DN genes after 72 h in culture. Taken together, these results demonstrate functional expression of K ir2.1 and K ir2.2 in rabbit ventricular myocytes and suggest that macroscopic I K1 is predominantly composed of K ir2.1 and K ir2.2 heterotetramers.