Many structures in complex organisms remain stable
at the system level despite continual turnover of
their biochemical components. For example, the human
heart does not grow new muscle fibers, but cardiac
muscle cells live for a extended periods of time,
exchanging their membrane and cytoplasmic proteins
continously. Likewise human neurons live for scores
of years, while again their proteins are being constantly
replaced. At the whole organism level, we see this
even more dramatically, as body form remains (in the
absence of failures of energy homeostasis caused by
the over availability of food in our culture) remarkably
contant over the adult human's lifetime. This poses
a general problem in biology: how to ensure stable
function and form in the face of continuous and massive
"parts replacement".
In recent years a number of laboratories at brandeis
have been studying this problem in the nervous system,
where it is easy to measure the consequences of molecular
turnover, by measuring synaptic receptor function
and the channels that produce electrical excitability.
The importance of homeostasis for the regulation of
intrinsic excitability and synaptic strength was pioneered
at Brandeis using a combination of experimental and
theoretical studies in the Eve
Marder, Gina
Turrigiano, and Sacha
Nelson laboratories.
