Figure 4

Expression of HCN isoforms in HL-1 cell cultures displaying contractile activity. Contractile activity in confluent HL-1 cell cultures was documented (dotted lines) before samples were immunostained with specific primary antibodies (see Additional file 1: Table S1) and fluorescently labeled secondary antibodies. Images of HL-1 cell contraction and immunostainings were superimposed based on underlying grids (see Additional file 1: Figure S3). Areas of contractile cell clusters are indicated by dotted lines. Immunolabeling of HCN1 (a), HCN2 (b), and HCN4 (c) is depicted. Arrowheads indicate some cells specifically stained for HCN isoforms. Scale bars specify 20 μm