Experiment Module: Confirming the Roles of an Ion, a Second Messenger, and an Enzyme in Long-Term Potentiation
Many methods have been used to determine the role of a particular ion, or a second messenger, or an enzyme in a synaptic process.
For example, the role of
calcium in long-term potentiation (LTP) has been confirmed in a number of ways.
One experiment involved injecting the postsynaptic neuron with chelating agents
such as EGTA and BAPTA, two molecules that bind to calcium and render it inactive.
As a result, it becomes impossible to induce LTP. he reverse procedure has also
been used. Researchers have injected special molecules into the postsynaptic neuron
and then illuminated them with UV light, thus causing them to release enough calcium
to induce LTP in this neuron.
Similarly, inhibiting PKA or CREB prevents LTP from reaching its second phase and being sustained.
In certain cases, researchers have even identified the one amino acid, among the hundreds of amino acids that make up a protein, whose phosphorylation is essential for LTP (Ser831 for the GluR1 sub-unit of the AMPA receptor and Thr286 for the autophosphorylation site of CaM kinase II).
Researchers have also shown that a mouse whose gene for the GluR1 sub-unit of the AMPA receptor had been knocked out could not have any LTP, thus confirming the role of CaM kinase II once again.
As for the mice for which site Thr286 in CaM kinase II was deactivated, their basic synaptic transmission was maintained, but LTP could no longer be induced in them, thus proving the need for CaM kinase II. The reverse procedure also led to the same conclusion: adding activated CaM kinase II to the pyramidal neurons of the hippocampus causes a potentiation phenomenon similar to LTP.
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