Expression of Kir2.1 and Kir6.2 transgenes under the control of the α-MHC promoter in the sinoatrial and atrioventricular nodes in transgenic mice

Kir2.1 and Kir6.2 are ion channel subunits partly responsible for the background inward rectifier and ATP-sensitive K⁺ currents (I_K1 and I_KATP) in the heart. Very little is known about how the distribution of ion channel subunits is controlled. In this study, we have investigated the expression (at protein and mRNA levels) of GFP-tagged Kir2.1 and Kir6.2 transgenes under the control of the α-MHC promoter in the sinoatrial node (SAN), atrioventricular node (AVN), His bundle and working myocardium of transgenic mice. After dissection, serial 10-μm cryosections were cut. Histological staining was carried out to identify tissues, confocal microscopy was carried out to map the distribution of the GFP-tagged ion channel subunits and in situ hybridization was carried out to map the distribution of corresponding mRNAs. We demonstrate heterologous expression of the ion channel subunits in the working myocardium, but not necessarily in the SAN, AVN or His bundle; the distribution of the subunits does not correspond to the expected distribution of α-MHC. Both protein and mRNA expression does, however, correspond to the expected distributions of native Kir6.2 and Kir2.1 in the SAN, AVN, His bundle and working myocardium. The data demonstrate novel transcriptional and/or post-transcriptional control of ion channel subunit expression and raise important questions about the control of regional expression of ion channels.