Lecture 4/5 Flashcards
Exam 2
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
Where does the intracellular water come from?
Aquaporins allow water to easily move both ways across cell membrane
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
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
How does the Na/K ATPase pump influence calcium levels?
Secondary active transport - provides the extracellular sodium in sodium calcium exchange (NCX) transporter
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
How much ATP is used in one round of Na/K ATPase pump?
1 ATP
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.
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
Why is there not a Vmax in simple diffusion?
Not a Vmax with simple diffusion because no conformation change; depends on electrochemical gradient
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
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.
How does osmotic pressure relate to osmolarity?
1 mOsm = 19.3 mmHg in 1L
What is the difference between osmolarity and osmolality?
Osmolarity - liters
- more practical
Osmolality - kg
What is Vrm?
Resting membrane potential (mV)
At rest, excitable cells are ______ compared to conditions outside of cell
Electronegative
When an excitable cell is “on” it is _______ inside the cell. When an excitable cell is “off” it is _______ inside the cell
Positive, negative
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
How does protein concentration impact Vrm?
- [Protein]i»_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.
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 (-)
Recite the Nernst (equilibrium) Potential equation
EMF = (+/-)61 x log([inside]/[outside])
What is the nernst potential?
Nernst Potential is the voltage that will prevent ions from diffusing across the membrane, down their concentration gradients.
At rest, what ions is the cell permeable to?
Sodium and potassium
Which ion influences resting membrane potential the most?
Potassium - permeability at rest to potassium is 10x more than sodium (P(Na) < P(K))
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 ______
- Close the activation gate
- 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
