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Now, we are coming to mechanisms
of excitability of astrocytes.
By definition,
astrocytes are electrically
non-excitable cells.
This means that they cannot
produce a regenerative
action potential.
That, of course,
is a function of
neurons in the nervous system.
However, astrocytes do have
their own mechanism
of excitability,
which is represented
by changes in
the cytosolic
concentration of ions
and second messengers.
Of course, ion number one
which is a reversal second
messenger in many different cells,
tissues practically
all over the universe
or the living universe on Earth,
this is calcium.
0:49
Let me start with a small
historical digression.
Calcium had been discovered by
Professor Humphry Davy in 1808.
That is the reason
for the name is
because Humphry Davy
demonstrated that
lime is a combination
of metal and oxygen;
hence, calcium from the
Latin word 'calx' for chalk.
The biological importance of
1:14
calcium ions had been
found some years later.
That was Sydney Ringer,
who, in the 1880s,
performed several experiments in
different tissues and species
which demonstrated incredible
importance at this time.
One of his most
amazing experiments
was also extremely simple.
He took some fish from
the fish market in London
and put them in
normal tap water.
Normal tap water
was from the Thames
and, of course, it
had everything and
those animals survived
without any major problems.
But then he transferred
some of these fish into
distilled water, which
doesn't have calcium,
and these animals started
to die very slowly.
In order to rescue them,
the only thing that was
necessary to do was to add
a minor amount of calcium
into the distilled water.
That was the very
first experiment that
demonstrated the importance of
calcium as an ion
of life and death.
