Calcium "Clamping"

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Bill Connelly
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Joined: Thu May 22, 2008 11:54 pm
Location: Australian National University

Calcium "Clamping"

Post by Bill Connelly »

Nature. 2010 Jan 14;463(7278):232-6.
Long-term potentiation depends on release of D-serine from astrocytes.

I'm trying to understand something from a recent paper and I knew this would be the place to ask. In that paper they state
However, exogenous Ca2+ buffers, although they suppress rapid Ca2+ transients, are unlikely to affect equilibrated (resting) free Ca2+ controlled by active homeostatic mechanisms. To constrain free astrocytic Ca2+ more efficiently, we ‘clamped’ its concentration at 50–80 nM, by adding 0.45 mM EGTA and 0.14 mM Ca2+ to the intracellular solution (Methods)19. Indeed, Ca2+ clamp abolished HFS-induced increases in Ca2+ concentration, which could be detected in astrocytes containing OGB-1 and EGTA only (Supplementary Fig. 2). Furthermore, biophysical simulations suggested that Ca2+ clamp could restrict Ca2+ nanodomains more efficiently than buffers alone
What they are saying is that by adding Ca2+ and a lower level of EGTA they are able to buffer calcium more effectively than Lots of EGTA alone (10 mM).

Looking at the reaction
Ca + Buff <--> Ca.Buff
I can't understand this.
By adding Ca2+ as well as lower levels of EGTA they are creating more Ca.Buff, so if something magically removed Ca2+ from the intracellular space, I can see how their method would help buffer against that. But how does having more free Ca2+ and More Ca.Buff help when Ca2+ floods the cell.
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