big lizards to astrocytomas
cells are shrunken, the sodium-proton exchanger is activated. It
mediates cell uptake of sodium and water until normal cell volume
is restored. At that point, it turns off.
cell volume isn't the only way this mechanism is activated.
hydrogen ion concentration inside the cell stimulates this enzyme,
which brings salt (sodium) and water into the cell as it removes
hydrogen ions. Consequently, the sodium proton exchanger also regulates
1980, Cala's lab was the first to identify this mechanism in living
cells, specifically the red blood cells of a large Louisiana salamander
known as amphiuma. Using microelectrodes, the team was able to monitor
electrical activity during volume regulatory sodium uptake in individual
red blood cells (each one about 35 times larger than a human red
discovered that the entry of positively charged sodium ions did
not change electrical activity. This finding, he recalls, was counter
to everything scientists thought they knew about sodium ion movement
across biological membranes.
Cala concluded that this electrically-neutral sodium transport was
the result of the sodium-proton exchanger.
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