RMP

Question 1

what is RMP

Answer 1

• All cells have electrical potential (voltage) differences across their plasma membrane (membrane potential)
• > Membrane potential of cells under resting condition is defined as resting membrane potential (RMP)

Question 2

why RMP ?

Answer 2

• Enables cells to function as batters – providing power to membrane proteins
• Exciteable cells (neurons, muscles…) large membrane potentials provide basis for signal transmission in form of depolarizing waves called action potentials

Question 3

measuring RMP

Answer 3

• Microelectrode is a fine glass pipette and filled with conducting solution (KCL)
• Membrane potential expressed as voltage inside the cell relative to outside the cell
• Measured in millivolts (1mV= 0,001V)

Question 4

RMP in different cell types

Answer 4

• Animal cells: negative potential at rest that ranges from -20 to -90 mV depending on cell type
• Cardiac and skeletal muscle cells have the largest RMP: -80 to -90 mV
• Nerve cells: -50 to -75 mV

Question 5

what determines RMP

Answer 5

• Ionic concentrations on either side of the cell membrane
• Ionic permeability of the cell membrane

Question 6

ion concentrations

Answer 6

• Ion selectivity and type of channels that are open make cell membrane selectively permeable to ions

Question 7

ion concentration for typical mamalian cell

Question 8

selective permeability of cell membrane

Answer 8

Phospholipid bilayer
- Hydrophobic interior
- Permeable to small uncharged molecules (O2. CO2, H2O, ethanol)
- Very impermeable to charged mole. (ions)

Question 9

ion channels

Answer 9

• Proteins that enable ions to cross cell membranes
• Aqueous pore through which ions flow by diffusion (passive transport)
  channel properties:
  1. Non-gated leak channels are always open
  2. Selectivity: for one or a few ion species – Na+, K+, Ca2+, Cl- ion channels
  3. Rapid ion flow: always down the electro-chemical gradient

Question 10

passive and active transport of ion across membrane

Answer 10

Passive:
- Ion channels
- Ions to diffuse down the conc. Gradient
- Selectively permeable to certain ions
Active:
- Actively (energy) move selected ions against conc. Gradient
- Create ion concentration gradients

Question 11

setting up the RMP

Answer 11

• chemical and electrical gradient
  -> - If the forces are equal there will be no net movement
  K+ is main ion affecting RMP, Na+ is 2nd most

Question 12

K+ chemical and electrical gradient

Answer 12

K+ inside (160 mM) —> K+ outside (4,5 mM)
electrical gradient is from extracellular to intracellular
-> when no net movement of K+ the RMP is negative

Question 13

Na+ chemical and electrical gradient

Answer 13

Na+ outside (150 mM) -> Na+ inside (15mM)
electrical gradient is from intracellular to extracellular
-> when no Na+ net movement RMP is positive

Question 14

Nernst equation

Question 15

other ions and membrane permeabilities

Answer 15

• Got their own ionic gradients and membrane permeabilities -> contribute to resting membrane potential
  Eg Na+ : Ena= +55 mV

Question 16

why is the RMP not -70 mV and not -20 mV

Answer 16

Neuronal membranes have high relative permeability to K+ because they have more K+ leak channels than Na+ leak channels

Question 17

calculating RMP for more ions: Goldman-Holding-Katz equation (GHK)

Question 18

RMP and EK

Answer 18

For most cells open K+ channels dominate the resting membrane permeability:
- Cardiac muscle (-80mV) and nerve cells (-70mV): RMP quite close to Ek
- Smooth muscle (-50mV): resting membrane potential not so close to Ek as there is lower membrane selecticity for K+
- Skeletal muscle (-90mV): RMP close to ECl and Ek as there is high membrane selectivity for K+ and Cl-

Question 19

Depolarizing and Hyperpolarization

Answer 19

a. Depolarization
- Decrease in size of membrane potential from normal value
- Cell interior becomes less negative
b. Hyperpolarization
- Increase in size of membrane potential from normal value
- Cell interior becomes more negative

Question 20

maintaining concentration gradients

Answer 20

Primary Role: The Na⁺/K⁺ pump is responsible for maintaining the concentration gradients of Na⁺ and K⁺ by actively transporting these ions across the cell membrane against their concentration gradients.

Mechanism:
The pump moves 3 sodium ions (Na⁺) out of the cell and 2 potassium ions (K⁺) into the cell for every ATP molecule consumed.
This active transport is critical because it works against the natural diffusion of these ions (i.e., Na⁺ tends to move inward and K⁺ tends to move outward).

Net Effect:
Sodium (Na⁺): High concentration outside the cell (~145 mM) and low concentration inside the cell (~10-15 mM).
Potassium (K⁺): High concentration inside the cell (~140 mM) and low concentration outside the cell (~5 mM).
The energy for this process comes from the hydrolysis of ATP (adenosine triphosphate), which provides the necessary power to move ions against their gradients.

Question 21

changing MP

Answer 21

Underlies many forms of signaling between and within cells:
1. Action potentials in nerve cells
2. Triggering and control of muscle contraction
3. Cell cycle re-entrance of post-mitotic cells
4. Transduction of sensory info into electrical activity by receptors
5. Postsynaptic actions of fast synaptic transmitters

Question 22

controlling ion channel activity

Answer 22

• Channels can open and close: gated
  1. Ligand gating
• Channel opens or closes in response to binding of chemical ligand eg channels at synapses that respond to extracellular transmitters and channels that respond to intracellular messengers
  2. Voltage gating
• Channel opens or closes in response to changes in membrane potential eg channels involved in action potentials
  3. Mechanical gating
• Channel opens or closes in response to membrane deformation eg channels in mechanoreceptors: carotid sinus stretch receptors, hair cells