Presence of the Kv1.5 K+ channel in the sinoatrial node

The aim of this study was to establish, using immunolabeling, whether the K v1.5 K+ channel is present in the pacemaker of the heart, the sinoatrial (S A) node. In the atrial muscle surrounding the SA node and in the SA node it self (from guinea pig and ferret), Western blotting analysis showed a major band of the expected molecular weight, similar to 64 kD. Confocal microsco py and immunofluorescence labeling showed Kv1.5 labeling clustered in atria l muscle but punctate in the SA node. In atrial muscle, Kv1.5 labeling was closely associated with labeling of Cx43 (gap junction protein) and DPI/II (desmosomal protein), whereas in SA node Kv1.5 labeling was closely associa ted with labeling of DPI/II but not labeling of Cx43 (absent in the SA node ) or Cx45 (another gap junction protein present in the SA node). Electron m icroscopy and immunogold labeling showed that the Kv1.5 labeling in atrial muscle is preferentially associated with desmosomes rather than gap junctio ns.