Session 4 Flashcards
Outline what a membrane potential is, how the resting potential of a cell
may be measured, and the range of values found
- What is a mp?
- How is the RMP measured i.e units?
- Give examples of the RMP is different cells
- magnitude of an electrical charge that exists across a plasma membrane and is always expressed as the potential inside the cell relative to the extracellular solution
- Millivolts (mV) [1mV = 10-3 V]
- – Cardiac and skeletal muscle: -80 to -95 mV
– Nerve cells: -50 to -75 mV
– Erthyrocytes have the smallest
What is the mp in skeletal muscle, erythrocytes and neurones
What instrument can be used to measure the mp?
The MICROELECTRODE is a fine glass pipette
Tip diameter is <1 µm
Can penetrate cell membrane
Filled with a conducting solution (KCl)
Explain the concept of selective permeability LO
Establishment of the membrane potential
Two factors are important for the generation of the membrane potential. They are:
• Asymmetric distribution of ions across the plasma membrane
– (i.e., ion concentration gradients)
• Selective ion channels in the plasma membrane
– K+, Na+, and Cl − channels are the most important channel types for most cells;
however, there are many cells in which other channels are important as well.
• (Can you name an extra one? Can you name two?)
Ion Channel properties:(3)
- Selectivity: for one (or a few) ion species. Na+, K+, Ca2+, Cl-, cation channels.
- Gating: the pore can open or close by a conformational change in the protein
- Rapid ion flow: always down the electrochemical gradient
Describe how the resting potential is set up given the distribution of ions across
cell membranes LO
What is the conc of Na+, K+ , Cl- and A- intra and extracellularly ?
Describe how the resting potential is set up given the distribution of ions across
cell membranes LO
What ion channel and ion sets up the resting membrane potential and how
- For most cells, open K+ channels dominate the membrane ionic permeability at rest.
- When these are equal and opposite, there will be no net movement of K+, but there will be a negative CHARGE across the membrane – i.e. the resting membrane potential
- Thus, the resting membrane potential arises because the membrane is selectively permeable to K+
How big would such a membrane potential be ?
If a membrane is selectively permeable to K+ alone, its membrane potential will be at ?
Ek
- That for most cells ? dominate the resting membrane permeability
- Ek =
- Extracellular:
- Intracellular:
- open K+ channels
- -95 mV (from Nernst equation)
- [K+] o = 4.5 mM
- [K+] i = 160 mM
Cardiac muscle (-80 mV), nerve cells (-70 mV):
Resting membrane potential is quite close to EK Not exactly at EK (less negative): ?
membrane not perfectly selective for K+
Cells with lower resting membrane potentials: Somewhat lower selectivity for K+ : increased contribution from other channels, e.g.
smooth muscle cells (-50 mV); erythrocytes virtually no selectivity for K+ (-9 mV)
Skeletal muscle:
Many ? open in resting membrane
Resting potential ≈ -90 mV
Close to both ?
Cl- and K+ channels
ECl and Ek
• To be able to outline the major physiological roles of:
– Sodium-potassium ATPase (Na+-K+-ATPase, ‘The Na pump’)
– Plasma membrane Ca2+ ATPase (PMCA)
– Sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA)
– Sodium calcium exchanger (NCX)
– Sodium hydrogen exchanger (NHE)
– Anion exchanger (AE)
- To be able to discuss how ion transporters work together in cell physiology
- To be able to discuss how ion transport contributes to:
– The control of resting intracellular Ca2+ concentration
– Cellular pH regulation
– Cell volume regulation
– Renal bicarbonate reabsorption
– Renal Na+ ion handling
Na+-K+-ATPase (Na pump) - Functions
- Forms Na+ and K+ gradients
– Necessary for electrical excitability
– (only contributes about - 5 mV to the resting membrane potential) - Drives Secondary Active transport
– Control of pHi
– Regulation of cell volume and [Ca2+]i
– Absorption of Na+ in epithelia
– Nutrient uptake, e.g. glucose or amino acids from the small intestine