It seems that in the Hippocampus there are two mechanisms that can
countereffect each other.
LTP [long term potentiation] which increases synaptic strength (larger
EPSC's which leads to larger EPSP's)
and LTD [Long Term Depression] that decreases synaptic strength.
In both mechanisms there seems to be a roll for Ca2+.
In LTP the post-synaptic [Ca2+] rises very high (up to 5 micromolar)
in LTD the post-synaptic [Ca2+] rises only slightly [lower than 1
So there you have it, these differences in concentration determine
what enzymes are used.
In LTP (with high concentrations Ca2+) Protein kinases are activated
LTD (with low concentrations Ca2+) Protein phosphatases are activated.
I'm lost here , how can this be?
How can this difference in concentration alone account for the choice
My guess is that there is some time dependence too.
In LTP there is a huge Calciumflux in a short period
whle in LTD there are small calcium fluxes in shorter periods.
Who knows more about the relation between Ca2+ concentration and
the activiation of kinases/phosphatases?