Transcript Lecture 21 (4/19/10) "Nerves and Ion Channels"

Announcements
Mid-term paper comments back today (Finally).
Homework #8 assigned today 4/19/10):
FRET, Nerves Due next Monday, 4/26/10
(Last one).
Wednesday, 4/21/10: Quiz on reading from
ECB, Nerves.
This Friday, 4/23/10: email your final topic
verbal and oral presentation. Include both a
write-up and PDF of the research paper. It
must be on a totally different topic (technique
and biology) than mid-term presentation. I will
get back to you by Monday 4/26/10.
Final Paper: due evening May 5th.
Final presentation—need two days (3 meetings):
Monday May 3rd, Wednesday May 5th, night of
Wednesday May 5th., 5pm (okay?) (Pizza included.)
Final Lectures: W, April 21st; M April 26th; W April 28th
how many different ion channels?
Ans:25-30,000 genes: 5000-6,000 genes. One or more
polypeptide/ion channel– could get less, or more, ion channels.
Ion Channels
0 mV (Outside)
0 mV (Inside)
open
(depolarized)
-60 to -100 mV (Inside)
closed (polarized)
Valium binds to serotonin (ligand) receptor
called GABA receptor– relaxes nerves.
Action Potential– Nerves Firing
http://www.biologymad.com/NervousSystem/nerveimpulses.htm
To close ion channels, to stop wave:
4. Na+ spontaneously close
5. K+ open  brings membrane potential back down
negative.
Gradient set-up by Na/K Transporters
[will go over]
Membrane permeant to only one ion
What is voltage (electrical potential)
in each case
Membrane permeant
to Na+
Membrane permeant
to K+
V>0 or <0?
Just a tiny amount of charge
causes potential, much less
than 15 mM or 150 mM.
What causes charge to stop flowing?
A sufficiently large force (electrical potential)
preventing more ions from going.
Given that V ~ -60mV and Na/K are two major ions,
which is your membranes permeant to? K+
What is Boltzmann’s Factor?:
Zexp(-Ei/kT)
Probability of being inside/outside? exp(Eout-Ein/kT)
e
Let f = voltage
Energy outside?
= q fout = 0
Energy inside?
= q fin
e
-
q = ? For Na+?
+59 mV if permeable only to Na+
If permeant to only K+,
resting potential =
-59 mV
http://www.biologymad.com/NervousSystem/nerveimpulses.htm
Is the Ion Channel Digital or Analog?
Charged amino acids (largely in
the voltage sensor) move.
K+
S3 S5S6
S2 S4
S1
Suggests model where 2 states that differ in energy by qV
Where q is about 13e, or 13e/4 per S1-S4 sub-unit; V= -80mV.
q is part of channel—gating current, not ionic current!
How does gate spontaneously shut-off?
How fast?
Nerve Impulse propagate, not spread,
because Na+ spontaneously shut-off.
Point mutation in Potassium
Gene that affects Potassium
Channel
Class evaluation
1. What was the most interesting thing you
learned in class today?
2. What are you confused about?
3. Related to today’s subject, what would you like
to know more about?
4. Any helpful comments.
Answer, and turn in at the end of class.