ensp;</span>subcellular <span  title="" class="an ">&ensp;</span>basis <span  title="" class="an ">&ensp;</span>for <span  title="" class="an ">&ensp;</span>a <span  title="" class="an ">&ensp;</span>recently <span  title="" class="an ">&ensp;</span>proposed <span  title="" class="an ">&ensp;</span>group <span  title="" class="an ">&ensp;</span>pacemaker <span  title="" class="an ">&ensp;</span>hypothesis <span  title="" class="an ">&ensp;</span>and <span  title="" class="an ">&ensp;</span>describe <span  t