<span  title="" class="an ">&ensp;</span>second <span  title="" class="an ">&ensp;</span>messenger <span  title="" class="an ">&ensp;</span>regulates <span  title="" class="an ">&ensp;</span>cellular <span  title="" class="an ">&ensp;</span>functions <span  title="" class="an ">&ensp;</span>throughout <span  title="" class="an ">&ensp;</span>the <span  title="" class="an ">&ensp;</span>photoreceptor <span  title="" class="an ">&ensp;</span>the <span  title="" class="an ">&ensp;</span>molecular <span  title=