Biomedical Engineering Reference
In-Depth Information
A patient is given enough Li
+
to raise his plasma concentration to 0.1 mM.
If lithium is permeable and at equilibrium across the plasma cell membrane,
what is the intracellular Li
+
for a cell that has a membrane potental of -80
mV?
3.5
3.6
A cat motor neuron has the following composition
K
+
ion
Na
+
ion
Cl
−
ion
Inside
150
15
9
Outside
5.5
152
124
(a) What is the resting potential if the membrane is permeable to only
Cl
−
ions?
(b) However, if the relative permeabilities are K
+
:Na
+
:Cl
−
1:0.04:0.45, then what is
the membrane potential?
(c) If you expose the cells to tetrodotoxin (from the puffer fish), which blocks
voltage-gated Na
+
ion channels, then what is the membrane potential?
(d) If you expose the cells to 4-aminopyridine, which blocks K channels (and has
been tried in MS patients as a means to overcome nerve conduction block), then
what is the membrane potential?
(e) What has to vary for the cell's membrane potential to shift to
−
50 mV?
3.7
A cockroach leg muscle has the following composition
K
+
ion Na
+
ion Cl
−
ion
Inside
110
27
44
Outside
27
111
150
(a) What is the resting potential if the membrane is permeable to only Na
+
ions?
(b) However, if the relative permeabilities are K
+
:Na
+
:Cl
−
1:0.04:0.45, then what is
the membrane potential?
(c) If you expose the cells to lidocaine, which block voltage-gated Na ion channels,
then what happens to the membrane potential?
(d) If you expose the cells to tetraethylammonium (TEA), applied to the inside of
a membrane, it will block voltage-gated K channels. Then what is the membrane
potential?
3.8
A cell has two pumps in its plasma membrane, both Na
+
dependent. One is a
Na
+
/CI symport, the other a Na
+
/glucose symport.
(a) By artificial means, you change the membrane potential from
−
80 mV to 0
mV. What effect will this have on the rate of operation of each pump? Note
that one of these pumps is electrogenic.
(b) You have two toxins, one that blocks each pump, but you do not know
which is which. How would you determine their identities by applying
each to the cell and measuring membrane potential only? Note that one of
these pumps is electrogenic.
