Week 5- ion channel physiology- Fitzakerley

Question 1

3 things help pass charged molecules through membrane

Answer 1

1) gap juntions
2) membrane transporters
3) ion channels

Question 2

differences b/t ion channels and transporters

Answer 2

Ion Channels:

• always passive flow- go down [ ] gradient
• just holes in the membrane
• can only pass small things (ions)
• transport at super high rates (millions/sec)
• USE [ ] GRADIENTS

Transporters

• can be passive or active flow (with or against gradient)
• never open to both sides at the same time
• transport big and small things
• transport is slower (100s/sec)
• ESTABLISH [ ] GRADIENT

Question 3

aquaporins

Answer 3

osmosis of H20
h20 flows from low soluble [ ] ⇒ high [ ]
2 important things about aqauporins
1) bidirectional flow
2) only H2O goes through channel (selective towards H2O)

Question 4

fundamental ion characteristics

Answer 4

selectivity and gating

Question 5

3 types of ion gating

Answer 5

1) mechanically
2) ligand
3) voltage

**always open is an option too (“leak”)

Question 6

3 levels of selectivity (what goes through ion channels)

Answer 6

1 and 2) Cation and Anion (all Na+, K+ and Ca2++ can go through one channel)

3) specific of Na+ OR K+ OR Cl-, etc (only 1 can go through)

Question 7

2 ways to stop ion flow

Answer 7

1) close gate

2) inactivate channel

Question 8

Which of the following is LEAST likely to pass through an individual channel?
Only Na+
Na+ and K+
Na+, K+ and Ca2+
Only Cl-
Na+ and Cl-

Answer 8

Na+ and Cl-

selectivity factors are usually based on charge

Question 9

Which of the following is LEAST LIKELYto be directly responsible for opening an ion channel?

• Membrane stretch
• Random changes in the position of the channel gate
• Depolarization of the cell membrane
• Change in extracellular ion concentration
• Binding of a drug to the channel

Answer 9

change in extracellular [ ], this is an example of indirect opening/closing

Question 10

What is the difference betweenclosing and inactivating a channel?

Answer 10

All gated channels can close; only some channels can inactivate.

Question 11

definitions:
depolarize
hyperpolarize

Answer 11

dep: make more (+)
hyp: make more (-)

Question 12

cells resting potential

Answer 12

all cells have a resting potential that is negative with respect to the extracellular fluid

Question 13

differences b/t electric and chemical gradients

Answer 13

electrical: (+) ion moves to (-) charge
chemical: set up by transporters and used by ions

Question 14

Identify the MOST ACCURATE ranking of EXTRACELLULAR ion concentrations.

Answer 14

Na+ > Cl- > K+ > Ca2+

Question 15

ion that likes to move from in ==> out

Answer 15

K+

Question 16

[ ] of K+ in and out of cell

Answer 16

in: 155 (muscle) and 140 (neurons)
out: 3.5-5

Question 17

function of Na+/K+ ATPase

Answer 17

establishment of the [ ] gradients for Na+ and K+ that are needed to generate resting, graded, and action potentials

Question 18

True or False: Each ion can only move in one direction across the cell membrane

Answer 18

false- move bidirectionally

Question 19

2 rules of ion movement

Answer 19

1) ions move in both directions thru channels

2) [ ] grad don’t change- electrical chemical gradients determine direction and mag of flow

Question 20

nernst equation

Answer 20

Eeq= 61/Z (log ( [ ]out/ [ ]in))

Question 21

The resistance to an ion’s movement across a membrane is primarily determined by:

transporters present on the cell surface.

ion channels that span the cell membrane.

metabotropic receptors found on the cell surface.

the ion concentrations on either side of the membrane.

the resting membrane potential

Answer 21

ion channels that span the cell membrane.
the number of open ion channels (particularly leak channels) is the primary determinant of the membrane resistance (the R in V=IR).

Question 22

what determines resting membrane potential

Answer 22

ION CHANNELS
transporters (like ATPase) set up gradients but only count for about -5 - -12mV of the membrane pot.
so… its ion channels that really determine the potential

Question 23

True or False: In neurons, the resting membrane potentials a constant negative value that is determinedby the activity of the Na+/K+ ATPase.

Answer 23

FALSE

1) not at a constant rate- homeostasis
2) transporters (like ATPase) only set up gradients but its ion channels that determine the resting membrane pot.

Question 24

Identify the major stages in the malaria transmission cycle, and the human cells that are infected during each stage

Answer 24

Mosquito bite → blood → liver (dormant) → blood → RBC (reproduction) → cause cell lysis that can reinfect other RBC → gameocyte that can infect other mosquitos

Question 25

what determines ion flow across the RBC membrane

Answer 25

1) presence of channels

2) electrochemical gradient

Question 26

Describe the changes in ion flow that prevent — and result — in RBC lysis during malaria infection

Answer 26

Anion transporters open → Cl- flows out, causing slight depolarization (to about -8)
K+ channels open → cause large hyperpolarization (to about -50ish or so)
Na+ channels open → causes large depolarization → once the membrane potential reaches -8, Cl- will start to flow in → this large increase in ions will cause water to follow and the cell will lyse

Question 27

Chemically, how do Na+, Cl-, and K+ want to move

Answer 27

Na+ and Cl- : INTO the cell

K+: OUT of the cell

Question 28

difference b/t chemical gradient and electric gradient

Answer 28

chemically: use the ion [ ] to determine this
Na+ and Cl- ALWAYS want to move in and K+ ALWAYS wants to move out
electrically: based on (+) charges moving towards (-) charges and vice versa