PROBLEMS
l. A rabbit gallbladder was filled with a solution containing 110
mM NaCl and a tiny amount of a neutral, impermeable dye, phenol
red.
It was suspended in a solution of 110 mM NaCl with identical
osmotic
pressure
and
the
following
data
obtained
(from
Diamond,J.M.: J. Gen. Physiol.,48:15-42, 1964):
t=0
t=120 min.
weight
2700 mg.
2220 mg.
Nai
110 mM
110 mM
phenol redi
0.2 ugm/ml
0.25 ugm/ml
1a.
200 mg. of the initial weight was tissue; what was the volume
of solution inside the gallbladder at t=0?
1b.
What was the volume after 120 minutes?
1c.
Has the amount of Na inside the cell changed?
1d.
Has the amount of phenol red inside the cell changed?
1e.
There
is
no
gallbladder wall.
membrane?
electrical
potential
By how much?
difference
across
the
Are Na+ and Cl- in equilibrium across the
Are there any passive forces that could cause a
movement of NaCl?
1f.
When
the
preperation
is
treated
with
iodoacetate, the weight remains constant.
loss in the non-poisoned gallbladder?
3
mMCN-
and
3
mM
What causes the weight
1g.
When 40 mM sucrose is added to the inner solution the rate of
weight gain fell by 50%. When 80 mM sucrose was added, the weight
did not change.
Why has the rate of water loss decreased as the
sucrose inside the gall bladder is increased.
1h.
If a gallbladder containing 80 mM sucrose and 120 mM NaCl
were poisoned with CN- and iodoacetate, what would be the rate of
weight change?
2.
Patients suffering from Hyperkalemic Periodic Paralysis show
attacks of severe weakness (including their respiratory muscles)
accompanied by high serum potassium.
from O.D. Creutzefeld et al.
The following values are
Electroencephalography and Clin.
Neurophysiol. l5:508-5l9, l963
Serum Resting
Normals
Potassium
Membrane
(mM)
Voltage
3.5
-879 mV
Patient A.S.
"strong",
3.75
induced attack,
6.9
- 686 mV
- 467 mV
spontaneous,,,
attack
5.2
The intracellular potassium is l50 mM.
- 536 mV
A.
Calculate the potassium equilibrium voltage in each case.
Does
the
resting
membrane
potential
approximate
the
potassium
equilibrium potential in any case?
B. Can we accept the assumption that K+ is the only permanent ion?
What other ion would you suspect?
PNa/PK in each case.
3.
Try calculating the ratio
What us the membrane basis of this disorder?
The potassium channels opening in Figure 5-5 had a potassium
ion gradient of Ko = 4.7 and Ki = l40.
equilibrium voltage?
What is the potassium
If the voltage across the cell membrane is
held at +30mV, what is the electrical energy available to do work
on the potassium ion?
In which direction will they move?
the conductance of this channel?
4.
a
What is
Remember S = I/E.
The Cai gated potassium channel recorded in Figure 4-9B shows
number
of
characteristic
features.
Neither
the
holding
potential (+20 mV) nor the potassium concentration (l00 mM on both
sides) changed; has changing Cai altered the conductance of this
channel?
Cai++?
Does the probability the channel will open alter with
Does Cai++ alter the duration the channel is open once it
has opened?
5.
The muscle fiber shown in Figure 4-6 (upper) has a volume of
0.85 mm2 in 0.l2 M NaCl.
When placed in 0.24 M NaCl the fiber
shrinks to a volume of 0.56 mm2.
What volume would you expect if
the muscle were placed in 0.24 M sucrose solution, in 0.l2 M AlCl3
solution?
6.
The internal potassium concentration of the squid giant
axon is 369 mM.
librium
Calculate values for the potassium equi-
potential
(E)
when
the
surrounding the axon contains:
200, and 500 mMK+.
potassium
in
the
fluid
l3 (normal sea water).
50,
The experimental values are found in:
A.L. Hodgkin and R.D. Keynes, J. Physiol., l28:6l, l955.
7.
The carotid body senses the partial pressure of oxygen in
arterial
blood
respiratory
brain stem.
calcium
and
and
and
provides
important
input
to
cardiovascular
regulatory
centers
of
the
the
Type I cells have voltage dependent sodium,
potassium
channels.
Decreasing
the
partial
pressure of oxygen (PO2) to very low (l0 mm Hg) levels does
not alter either the sodium or calcium channels but reduces
the open time of potassium channels 25 to 50%.
This effect
is reversible when the cells are returned to high (l50 mm Hg)
PO2.
a. What effect would you expect low PO2 to have on the
resting membrane potential of Type I cells?
Lopez-Borneo, J. et al.
Data from
Science 24l:580-582, l988.