Ion channels and Ion Transport (2)

Question 1

What are the 3 major groups of ion channels?

Answer 1

Mechanosensitive, voltage-gated, and chemosensitive (ligand-gated)

Question 2

What kind of conformational change do carrier proteins go through?

Answer 2

Substrate induced because they have a binding site for the transported molecule

Question 3

What kind of transport can carrier proteins mediate?

Answer 3

Both active and passive transport

Question 4

What kind of transport can channel proteins mediate?

Answer 4

Only passive transport

Question 5

What are ion channels?

Answer 5

Transmembrane proteins that connect the intracellular and extracellular environments

Question 6

What is the distinction between different ion channels?

Answer 6

They are distinguished by the ion that passes through them and the mechanisms which cause them to open

Question 7

When do mechanosensitive channels open?

Answer 7

When sensory endings are stretched

Question 8

When do voltage-sensitive channels open?

Answer 8

In response to a change in the membrane (electrical) potential

Question 9

When do chemosensitive (ligand-gated channels) open?

Answer 9

When they bind neurotransmitters, hormones or intracellular chemicals to the extracellular surface of the channel

Question 10

What is mechanosensation important for?

Answer 10

Sensory perception, proprioception, and sensing changes in blood pressure

Question 11

What are some characteristics of mechanosensitive channels?

Answer 11

Nonselective cation channels, impermeable to proteins, and the influx of ions when open cause changes in membrane potential

Question 12

What are the types of voltage-sensitive ion channels?

Answer 12

Voltage-gated K+ channels, Voltage-gated Na+ channels, Voltage-gated Cl- channels, and voltage-gated Ca2+ channels

Question 13

What do voltage gated K+ channels do?

Answer 13

They are responsible for bringing the cell to its resting membrane potential and the maintainance of that resting value

Question 14

What do voltage gated Na+ channels do?

Answer 14

They are responsible for the depolarization of the action potential

Question 15

What do voltage gated Cl- channels do?

Answer 15

They are poorly understood but are known to have a role in kidney regulation

Question 16

What do voltage gated Ca2+ channels do?

Answer 16

They increase the intracellular calcium levels necessary for muscle contraction and calcium signaling

Question 17

Name some examples of ligand-gated channels

Answer 17

Acetylcholine receptor channels: nicotinic receptor channels, CNS postsynaptic channels: glycine, GABA and serotonin channels, ATP-sensitive (purinergic) of P2X receptors, and Inositol triphosphate (IP3) and ryanodine receptors

Question 18

What do agonists do?

Answer 18

Activate the channel to produce an electrical signal

Question 19

What do antagonists do?

Answer 19

Bind to the channel and prevent channel opening

Question 20

What does the cell membrane serve as?

Answer 20

An insulator to prevent movement of electrical charges to prevent ions from moving back and forth between intracellular and extracellular compartments

Question 21

What does the membrane potential difference reflect?

Answer 21

The separation of charge across the membrane

Question 22

In regards to the membrane how are the charges allocated?

Answer 22

The inner surface of the membrane has a net negative charge and the extracellular side has a net positive charge

Question 23

What is membrane potential?

Answer 23

The voltage difference that exists between the inside and outside of the cell. Vm=Vo-Vi

Question 24

What causes K+, Na+, Ca+, and Cl- to move across the cell membrane?

Answer 24

The concentration gradient for each ion and the electrical (gradient) difference. The sum of these 2 factors is the electrochemical gradient or the electrochemical potential

Question 25

What generates an ionic current?

Answer 25

The net movement of an ion across the membrane

Question 26

What is the net flux of an ion through the membrane?

Answer 26

The electrical current Ix. Ix=gx(V-Ex) V-Ex is the driving force of the magnitude for ion movement for ion x gx is ion conductance

Question 27

When does an inward current result?

Answer 27

When there is an influx of positive charges or an efflux of negative charges

Question 28

When does an outward current result?

Answer 28

When there is an efflux of positive charges or an influx of negative charges

Question 29

When does an equilibrium (reversal) potential occur?

Answer 29

When the net current is zero (no net movement of that ion because it reached equilibrium). Each ion has its own equilibrium potential

Question 30

When is the Nerst equation used?

Answer 30

``` To determine equilibrium potential for a given ion. Eion(in mV)=61/z*log[ion]out/[ion]in Eion=equilibrium potential of the ion z=charge of the ion [ion]out=extracellular concentration [ion]in=intracellular concentration ```

Question 31

What is the resting membrane potential (RMP)?

Answer 31

The membrane potential difference for a cell at rest. It is established by charge and concentration for ions that can move across the membrane

Question 32

What are some different cell types and their membrane potentials?

Answer 32

Skeletal and cardiac muscle= -90 mV Sensory/motor neurons= -70 mV Smooth muscle= -60 mV Red blood cells= -10 mV

Question 33

What ion is the resting membrane potential mainly permeable to?

Answer 33

K+ because the RMP is close to the equilibrium potentials for K+ when the cell is at rest

Question 34

What contributes to the resting membrane potential?

Answer 34

Potassium leak channels allow the efflux of potassium at rest and they continue to flow until the cell reaches the potassium equilibrium potential. Sodium leak channels allow a small influx of sodium ions so the cell never reaches the potassium equilibrium potential

Question 35

Does calcium play a major role in the resting membrane potential of most excitable cells?

Answer 35

No

Question 36

What is the basic mechanism for transmission of information in the excitable cells (nerve and muscle cells)?

Answer 36

Action potentials. Most are the result of changes in sodium and potassium ion movement in these cells. In cardiac cell action potentials also involve Ca2+

Question 37

How fast do action potentials occur in nerve and muscle cells compared to cardiac cells?

Answer 37

Nerve and muscle: ~1 millisecond | Cardiac: hundreds of milliseconds

Question 38

What is depolarization?

Answer 38

The process of making the membrane potential less negative

Question 39

What is repolarization?

Answer 39

The process of making the membrane potential more negative (brings the membrane potential back to the resting value)

Question 40

What is hyperpolarization?

Answer 40

The process of making the membrane potential more negative (usually more negative than the resting membrane potential)

Question 41

What is threshold potential?

Answer 41

The membrane potential at which the action potential will fire

Question 42

What is overshoot?

Answer 42

The portion of the action potential where the membrane potential is positive

Question 43

What is hyperpolarizing afterpotential (undershoot)?

Answer 43

The portion of the action potential where the membrane potential is more negative to the cell at rest

Question 44

What is the refractory period?

Answer 44

The period during which another normal action potential cannot be elicited

Question 45

Can graded potentials become action potentials?

Answer 45

Yes potentially

Question 46

What are the subdivisions of the refractory period?

Answer 46

Absolute refractory period: the time during which no stimulus regardless of its size, can stimulate an action potential Relative refractory period: when a larger than normal stimulus can develop an action potential (usually abnormal in shape)

Question 47

What are the 4 methods of local communication between cells?

Answer 47

Gap junctions, contact dependent signals, autocrine signaling, and paracrine signaling

Question 48

What are gap junctions?

Answer 48

Junctions formed from the union of connexins that serve as a cytoplasmic bridge between neighboring cells. They allow the transfer of chemical and electrical signals from cell to cell and play an important role in the conduction of action potentials of cardiac muscle

Question 49

What are contact-dependent signals?

Answer 49

They occur by the direct interaction between 2 cells. A surface molecule on one cell binds to the receptor of another cell and they are important in the immune system and play a role in cell-adhesion processes

Question 50

What is autocrine signaling?

Answer 50

Occurs when a chemical signal that is released acts on the same cell that initiated the signal. The cell acts on itself

Question 51

What is paracrine signaling?

Answer 51

Occurs when a chemical signal is released and it acts on neighboring cells (near the site of release)

Question 52

How does the endocrine system work?

Answer 52

It uses hormones (chemical signals) that are released into the blood to act on specific cell receptors that are located in many places in the body

Question 53

How does the nervous system work?

Answer 53

It uses both chemical and electrical signals to communicate with cells and specific cell receptors in the body

Question 54

How do lipophilic molecules work?

Answer 54

They diffuse across the plasma membrane and bind to intracellular receptors to alter gene transcription and protein synthesis

Question 55

How do hydrophilic molecules work?

Answer 55

They can't cross the plasma membrane so they bind to receptors located in the cell membrane to elicit an intracellular response

Question 56

What are the 4 categories of membrane receptors?

Answer 56

Receptor channel-ligand binding opens or closes the channel Receptor enzyme-ligand binding to a receptor-enzyme activates an intracellular enzyme G protein-coupled receptor-ligand binding to a G protein-coupled receptor opens an ion channel or alters enzyme activity Integrin receptor- Ligand binding to integrin receptors alters the cytoskeleton

Question 57

What kind of signaling is an example of a receptor-enzyme linked signaling pathway?

Answer 57

Tyrosine kinase signaling

Question 58

Tyrosine kinase signaling is an important component of what actions on the body?

Answer 58

Insulin, growth hormone, and insulin-like growth factor-1