00:01
So let’s start off with pores.
00:03
So pores are very nice in terms
of they’re usually very fast.
00:09
however, they’re not regulated
in quite the same way.
00:12
In fact, usually, when they are inserted
in the cell membrane, they are open,
although you can modulate
this a little bit from
time to time with
protein-protein interactions.
00:23
So think of this a
lot like a funnel.
00:27
You have a funnel in
the cell membrane,
you pour something like
water into it and it
moves directly through
that cell membrane.
00:36
Now, aquaporins are
these molecules
and they are located throughout the body.
00:42
There are 13 primary types of aquaporins
and we label those from 0 to 12,
and they are in various
densities in different tissues.
00:52
So, adipocytes or fat cells
have this aquaporin 7 in them.
00:58
Blood have more specific type
of aquaporins, 1, 3, and 9.
01:04
The central nervous system
or brain has 1, 3, 4, and 5.
01:10
The skin has aquaporin 3.
01:13
Skeletal muscle uses aquaporin 4.
01:16
The lungs use 3, 4, and 5.
01:19
And finally, the kidney uses 1, 2, 3, 4, and 7.
01:25
We’re going to spend the prototype
time in this particular pore
talking about aquaporin 2, which is
located primarily in the kidney.
01:36
So how do aquaporin 2s work?
Well, these are going to be water
channels, and in the kidney,
you want to move water
from the apical membrane
or from the apical lumen side, across
the apical membrane, into the cell.
01:51
This allows you to
reabsorb water.
01:55
And why do you want
to reabsorb water?
So you don’t dehydrate, so you can have as
much water within the system as you can.
02:02
If you don’t reabsorb water, you’ll
end up peeing it or urinating it out.
02:08
How do these work?
These are all in the apical membrane
here allowing water transport to move,
but you need to have an osmotic
gradient for water to move.
02:18
What determines water
transport is basically the
density of aquaporin 2
channels on this membrane.
02:25
The more channels you have, the more water
will move if you have an osmotic gradient.
02:29
The less channels you have, the less
water will move if that gradient exist.
02:34
How do you regulate the
amount of aquaporin channels?
It’s primarily by a vesicle
membrane insertion.
02:42
So, in response to a
stimulus, in this case,
it’s using antidiuretic hormone
also known as arginine vasopressin.
02:51
You signal these vesicles
with aquaporins in them
to fuse within the membrane of
that apical side of the cell.
03:02
It has in it aquaporins, so how
you regulate this is you just
butt and insert this particular
vesicle within that apical
membrane and that increases the
density of cell transporters.
03:17
How does this process work?
It can be seen here, where
you need to have binding of
this arginine vasopressin
to a particular receptor
and then through a
signaling process,
you will both make
more aquaporin 2
and cause phosphorylation
of various proteins to
make these vesicles dock and
fuse on the apical membrane.
03:44
And this is how this kind of pore system
works and how aquaporin 2 channels
importantly affect body-fluid
balance in the kidney.