class="an ">&ensp;</span>participation <span  title="" class="an ">&ensp;</span>of <span  title="" class="an ">&ensp;</span>these <span  title="" class="an ">&ensp;</span>two <span  title="" class="an ">&ensp;</span>classes <span  title="" class="an ">&ensp;</span>of <span  title="" class="an ">&ensp;</span>channels <span  title="" class="an ">&ensp;</span>at <span  title="" class="an ">&ensp;</span>different <span  title="" class="an ">&ensp;</span>stages <span  title="" class="an ">&ensp;</span>of <span  