</span>block <span  title="" class="an ">&ensp;</span>presynaptic <span  title="" class="an ">&ensp;</span><span  title="ProteinName" class="an ProteinName">Ca</span><span  title="" class="an ">&ensp;</span>channels <span  title="" class="an ">&ensp;</span>while <span  title="" class="an ">&ensp;</span>whole <span  title="" class="an ">&ensp;</span><span  title="Neuron" class="an Neuron">cell</span><span  title="" class="an ">&ensp;</span>voltage <span  title="" class="an ">&ensp;</span>clamp <span  title="