Hl-1 Cardiomyocytes As A Tool For The Study Of Regulation Of Kir3.1/Kir3.4 Channel Activity

The KAch channel slows the heart rate it in response to acetylcholine (ACh). Binding of ACh to the M2 Muscarinic receptor triggers Gβγ-mediated activation of the cardiac GIRK1/GIRK4 inwardly rectifying K channel, which is a heterotetrameric complex of the Kir3.1 and Kir3.4 subunits. Several reports, including work from our laboratory, suggest that phosphorylation events may be critical determinants of the above regulation. Apart from the heterologous expression of the channel subunits in various systems, primary atrial cultures have been so far the only available system for such studies. The development of a cardiomyocyte cell line (HL-1) which has the ability to continuously divide while maintaining a differentiated cardiac phenotype, prompted us to examine whether it could be used for studies on the regulation of GIRK1/GIRK4 channel activity. Here we report that HL-1 cells express both the Kir3.1 and Kir3.4 subunits, antibodies raised against each subunit co-immunoprecipitate the other subunit, the cells respond to ACh and growth factor receptor stimulation, show KAch currents and display electrophysiological properties characteristic of atrial KAch. Our data indicate that the HL-1 cell line provides a useful tool for the dissection of mechanisms regulating GIRK1/GIRK4 activity in vivo.