ent <span  title="" class="an ">&ensp;</span>defined <span  title="" class="an ">&ensp;</span>by <span  title="" class="an ">&ensp;</span>coassembly <span  title="" class="an ">&ensp;</span>of <span  title="" class="an ">&ensp;</span><span  title="CAP" class="an CAP">HCN</span><span  title="" class="an ">&ensp;</span>and <span  title="" class="an ">&ensp;</span><span  title="CAP" class="an CAP">HCN</span><span  title="" class="an ">&ensp;</span>subunits <span  title="" class="an ">&ensp;</span>and <span  ti