Lecture 4/5 Flashcards by Michael Sokol

Where does the intracellular sodium come from for the Na/K ATPase pump?

Sodium is allowed into cell via secondary active transport processes (3Na+/1Ca++ exchange)
Sodium leakage at rest (simple diffusion)
Action potential - sodium comes in

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Where does the intracellular water come from?

Aquaporins allow water to easily move both ways across cell membrane

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Describe the cell diuretic feature and its involvement in the Na/K ATPase pump

Keeps cell osmolarity in check - moves water ICF → ECF with sodium
- responsible for intracellular volume control

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Describe cellular edema and how to fix it

Sick patient low on ATP → Na/K ATPase pump doesn’t work as well → ICF increases → swelling
- Very hard to fix, have to fix cellular ATP levels in order to fix problem

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How does the Na/K ATPase pump influence calcium levels?

Secondary active transport - provides the extracellular sodium in sodium calcium exchange (NCX) transporter

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Describe how the Na/K ATPase pump works against the electrochemical gradient

Na+ movement is against concentration and electrical gradient
K+ movement is only against concentration gradient

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How much ATP is used in one round of Na/K ATPase pump?

1 ATP

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Compare a graph of facilitated vs simple diffusion rates

Simple diffusion increases linearly w/ increases in [] gradient.
Facilitated diffusion increases w/ increased [] gradient until all transporter proteins are saturated and transporting as fast as possible.

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What is the Vmax in facilitated diffusion? Why is there a Vmax?

Vmax - max speed the transporters can diffuse
- conformation change can only happen so fast

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Why is there not a Vmax in simple diffusion?

Not a Vmax with simple diffusion because no conformation change; depends on electrochemical gradient

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What are the 8 factors that effect diffusion rate?

[Concentration]inside vs [Concentration]outside cell (chemical gradient)
Membrane (lipid) solubility
Size of the particle
Size of the pores for travel
# of pores for travel
Kinetic movement (heat)
Physical pressure
Electrical charge

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What is osmotic pressure?

Osmotic pressure is the physical pressure (force) required to prevent osmosis from occurring through a semipermeable membrane into an osmotically-active solution.

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How does osmotic pressure relate to osmolarity?

1 mOsm = 19.3 mmHg in 1L

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What is the difference between osmolarity and osmolality?

Osmolarity - liters
- more practical
Osmolality - kg

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What is Vrm?

Resting membrane potential (mV)

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At rest, excitable cells are ______ compared to conditions outside of cell

Electronegative

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When an excitable cell is “on” it is _______ inside the cell. When an excitable cell is “off” it is _______ inside the cell

Positive, negative

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What causes resting membrane potential?

Na/K pump and selective permeability of membrane (distribution of proteins)

differences in the concentrations of ions (particularly Na/K) inside and outside the cell

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How does protein concentration impact Vrm?

[Protein]i&raquo_space; [Protein]o - more proteins inside cell wall than outside cell wall
Proteins often carry a net negative charge.
Proteins are also an important intracellular buffer
Many proteins aligned at the cytosolic face of the cellular membrane.

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What charge do proteins usually have? Why?

Proteins are made from amino acids (more (-) amino acids than (+)) → proteins typically have net negative charge
- makes ICF (-)

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Recite the Nernst (equilibrium) Potential equation

EMF = (+/-)61 x log([inside]/[outside])

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What is the nernst potential?

Nernst Potential is the voltage that will prevent ions from diffusing across the membrane, down their concentration gradients.

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At rest, what ions is the cell permeable to?

Sodium and potassium

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Which ion influences resting membrane potential the most?

Potassium - permeability at rest to potassium is 10x more than sodium (P(Na) < P(K))

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At rest, K+ is _______ the cell

Leaving - Wants to go from area of higher concentration to lower

At rest, Na+ is _______ the cell

Entering - Wants to go from area of higher concentration to lower

Describe how the EMF of potassium effects the polarity of the cell (EMF = -90 mV)

Potassium leaving the cell will cause the ICF charge to become more electronegative

Describe how the EMF of sodium effects the polarity of the cell (EMF = 61 mV)

Sodium entering the cell will cause the ICF to become more positively charged

Overall membrane potential of the cell will be ______

closer to K+ → -80 mV

If an excitable cell wants to become active, it will allow more ______ to enter the cell

Sodium - makes ICF more positively charged (depolarization)

What is the difference between the Nernst and Goldman equations?

Nernst - membrane potential for 1 electrolyte Goldman - membrane potential for multiple ions; dependent on concentration and permeability of individual electrolytes

How does the Goldman equation relate ion concentration and permeability?

Each [ion] gradient contributes only as much as the membrane is permeable to each ion.

Cell adjusts ________ to adjust the membrane potential

ion permeability (ion channels)

mEq/solution and mOsm/solution are a measurement of

quantity/volume

The reason that not all of the water in the U shape test tube flows to one side despite there being no solute on one side is ____________

gravity

The net ion change for one cycle of the sodium potassium ATPase pumps is

ICF becomes (-) by the charge of 1 ion with one cycle of a single Na K ATPase cycle (loses 3+, gains 2+)

Water follows ______

sodium

What happens to the membrane potential of a cell if the concentration of ICF:ECF of potassium decreases?

The lower end of the membrane potential will be higher (-70 instead of -90), making the overall resting membrane potential higher (-60 instead of -80)

What channels determine the action potential?

- Voltage-gated "Fast" Na+ channels, depolarization - Voltage-gated "slower" K+ channels, repolarization

What is the membrane potential when sodium rushes in and the cell hits action potential?

+35

What will high K+ do the the heart?

EKG changes (V-fib) - lowers the rate of repolarization because the ICF is less (-)

What cells are highly permeable to chloride ions?

Neurons

Is a more electronegative resting membrane potential easier or harder to excite than a more electropositive RMP?

more negative = harder (hyperpolarization) more positive = easier

RMP and permeability is dependent on ________, not ________

Diffusion through channels, not Na+/K ATPase pump

Resting cells are said to be ________

Polarized (-mV @ Vrm)

A difference in electrical charge between inside and outside of cell is __________

Polarization

To become less polar (or more + charged); usually = stimulated or turned on is ________

Depolarization

To become more polar (or more–charged) than Vrm; usually = inhibited (or more–charged and more difficult to excite __________

Hyperpolarization

__________ is to return to Vrm from a depolarized state

Repolarization

Hyperpolarization can occur when?

At rest (change in permeability) or after depolarization

Why doesn't depolarization reach +60mV?

Because K+ channels never fully close

What is the purpose for the plateau in action potentials in the heart?

Action potential sustained longer - period of time spent in action potential decides how well heart is going to pump (myocardial muscle contraction)

What is conductance?

How much ion flow or how much potential current does the cell have - inverse of resisitence - the relative ease at which an ion can cross the membrane

During repolarization, the cell opens _______ to speed up the process

Additional K+ channels (Voltage-Gated) until back to RMP

Why does hyperpolarization occur?

Result of extra K+ channels staying open until return to RMP

Why would the cells want to repolarize the cell quickly?

Send messages quickly (nervous system)

___________ results in more V-G Na+ channels opening during depolarization

Positive feedback

What causes the plateau of depolarization of action potentials in the heart?

Influx of calcium

How positive would the membrane potential need to be to prevent Na+ from entering the cell?

+61 mV

How negative would the membrane potential need to be to prevent K+ from leaving the cell?

-90 mV

A RMP of -80 mV prevents ______ even though there is relatively high permeability

K+ from leaving the cell; because (+) want to stay in (-)

A RMP of -80 mV encourages ______ even though there is relatively low permeability

Na+ to enter the cell; because (+) wants to move towards (-)

Cell membrane doesn't actually need current, cells just need the ________

Potential for current

Usually, the potential for current ends up creating _______

Current

If an electrolyte with a negative charge has an equilibrium potential of -50 mV, what would the electrical/concentration gradient look like if the Vrm is -80 mV?

Higher concentration outside Vrm would push the electrolyte out of cell

What is equilibrium potential?

The charge required in the inside of the cell to prevent the movement of an ion down its concentration gradient (+61 mV for Na+)

Any drug that ends in _______ effects the V-G Na+ channels

- caine (many anesthetics)

What are the different V-G sodium gates doing at rest?

Activation/Outside gate - closed at rest (M-gate) Inactivation/Inside gate - open at rest (H-gate)

In V-G Na+ channels, as the activation gate is opening, this triggers the ________

Inactivation gate to close

After polarization, the membrane must ________ to open the inactivation gate.

Repolarize

If you don't have normal resetting after an action potential, the cell won't be able to ______

Refire

When repolarizing, the activation gate has to ______ first and then the inactivation gate ______

1. Close the activation gate 2. Reopen the inactivation gate - if not in this order, both gates would be open and sodium would rush in

V-G K+ channels are _______ to open than the Na+ channels

Slower - also slower to close (hyperpolarization)

At rest, the V-G K+ gate is _______

Closed

_______ opens the V-G K+ gate

Depolarization

The nicotinic (ACh-R) channel/receptor is an example of _________

Depolarizartion - 2 ACh bind nACh-R - Negatively-charged ion pore opens. - Positive ions flow in - More Na+ flows in than K+ flows out

The muscarinic (mACh-R) is an example of ________

Hyperpolarization - AV Node in heart - GPCR is coupled directly to a K+ channel. - More K+ channels open: more polar - More polar = hyperpolar(ized)

The driving force of an ion depends on 3 things:

charge of ion, concentration gradient of ion, and charge of ICF

What channels are usually effected by anesthetic drugs?

Fast Na+ channels - make it harder to reset itself

V-G K+ channel gates are located on the ______ of the cell

inside

Lecture 4/5 Flashcards

Exam 2