">&ensp;</span>rapidly <span  title="" class="an ">&ensp;</span>than <span  title="" class="an ">&ensp;</span><span  title="CAP" class="an CAP">HCN</span><span  title="" class="an ">&ensp;</span>channels <span  title="" class="an ">&ensp;</span><span  title="CAP" class="an CAP">HCN</span><span  title="" class="an ">&ensp;</span>channels <span  title="" class="an ">&ensp;</span>also <span  title="" class="an ">&ensp;</span>activate <span  title="" class="an ">&ensp;</span>at <span  title="" class="an ">&ensp