L4: Channels & Transporters

Question 1

Explain the patch clamp technique

Answer 1

• studies microscopic currents by using a glass micropipette as an electrode
• the glass micropipette is pressed against membrane
• the interior of the pipette is filled w/ soln matching ionic composition of bath soln
• a chlorided silver wire is placed in contact w/ soln and conducts electric current
• no leakage from seal due to the high resistance of seal

Question 2

What did the patch clamp technique help us detect?

Answer 2

detect currents flowing thru single membrane channels due to depolarization

Question 3

What did the patch clamp technique show about Na+ & K+ channels?

Answer 3

Na+ Channels

• opening is voltage dependent
• open near beginning of A.P
• inactivate
• current reverses at ENA
• TTX blocks Na+ channels

K+ Channels

• opening is voltage dependent
• open later than Na+ channels
• TEA or Cs+ block

Question 4

List the 4 different types of K+ channels

Answer 4

1 - Kv2.1 channels involved in repolarization; show little inactivation

2. Kv4.1 channels inactivate rapidly to depolariation
3. inward rectifiers allow more current flow during hyperpolarization
4. Ca2+ activated K+ channels

Question 5

Difference btw voltage-gated & ligand gated channels

Answer 5

Voltage gated channels (Na+, K+, Ca2+, Cl2- channels) - selectively permeable while ligand activated channels respond to chemical signals and can allow 2 or more types of ions through

Question 6

List the 3 diseases that are associated with voltage gated Ca2+ channelopathies

Answer 6

• congenital stationary night blindess
• familial hemiplegic migraine
• episodic ataxia type 2

Question 7

List a Na+ channelopathy

Answer 7

Generalized Epilepsy w/ Febrile Seizures

Question 8

List a K+ channelopathy

Answer 8

Benign familial neonatal convulsions

Question 9

List the 2 toxins that block Na+ channels

Answer 9

• TTX

- Saxitoxin

Question 10

List the toxins that prolong durations of Na+ currents

Answer 10

alpha-toxins

Question 11

List the toxins that shift voltage activation of Na+ channels

Answer 11

beta-toxins

Question 12

List the toxins that inactivate Na+ channels

Answer 12

Batrachotoxins

Question 13

List the 2 toxins that block K+ channels

Answer 13

dendrotoxin

apamin

Question 14

List the 2 Ca2+ channel toxins

Answer 14

conotoxins

agatoxins

Question 15

Compare and contrast ATPase pumps, ion exchangers

Answer 15

ATPase pumps - directly use ATP to move ion against concentration gradient
ion exchangers - tranport ions in opposite direction using the energy from the ion that is going down its concentration gradient

Question 16

Compound action potentials are not all or none. List 4 characteristics of compound action potentials

Answer 16

• require voltage dependent Na+ and K+ channels for generation
• can be Monophasic or biphasic
• possess a refractory period
• voltage is sum of all or none action potentials generated by individual nerve fibers

Question 17

The patch clamp technique:
A) with the inside out recording clamps the membrane at a particular voltage and measures current flow through a neuron’s patch of membrane channels.

B) clamps the membrane current to a particular amperage and measures voltage changes caused by current flow.

C) when employed with inside out recordings can record multiple voltage depolarizations that produce microscopic currents which when summed approximate macroscopic currents in form.

D)A and C are correct.

E) All of the above are correct.

Answer 17

D