HUBS1403 Lecture Notes - Lecture 23: Voltmeter, Choline, Skeletal Muscle
8 Jun 2018
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Ion Channels and Resting Membrane Potential
Membrane Proteins
Membrane proteins are major determinants of all cell function
• Lipids help together by hydrophobic and hydrophilic forces
• These forces also hold transmembrane proteins in the membrane
There are 6 types of transmembrane proteins:
1. Anchoring proteins
2. Recognition proteins
3. Enzymes
4. Receptor proteins
5. Carrier proteins
6. Channel proteins aka ion channels
Critical determinant of transmembrane ion movements (and thus ion concentrations)
Typical ion concentration (mM-mini Molar) in intracellular fluid (ICF) and extra cellular fluid (ECF)
(precise values vary from text to text)
• Concentration in neurons is just like other cells
• Cells only like internal K+
• They do not like high levels of Na+ and Ca2+ in cytoplasm
• Ca2+ = signalling ion
There are 165 positive ions inside the cell compared to 5 negative, how does this work?
• There are many proteins inside cells and they carry a slight negative charge
Establishing Concentration Gradients
Eg Na/K exchange pump
The ATP driven Na/K exchange pump establishes Na and K concentration gradients that are critical
to establishment of membrane potential
• Na and K both move "uphill" against their concentration gradients
How do concentrations get established?
• Energy in ATP used to drive Na+ and K+ from low to high concentrations
Ions can also diffuse "downhill" if ion channels open
• Channels differ in their ion selectivity (eg Na, K, Cl, monovalent cations, non-selective etc.)
depending on the pore size and array of charges along the proteins that form the pore
• Ions don’t like the lipid bilayer so they will not cross the PM unless through a water filled
channel
Ion selectivity and gating mechanism nomenclature,
• Ion channels are selective about which ions pass through. Channels are named after the most
permeant ion found in the cell.
How ion channels a highly selective yet have high ion throughput has only been
Solved in the last 10 years.
Leaky vs Gated Ion Channels
Channels are also named according to the means of opening and closing (gating)
• Leak - unregulated, will open an close at intervals with no particular stimulant or inhibitor
Document Summary
Membrane proteins are major determinants of all cell function. Lipids help together by hydrophobic and hydrophilic forces: these forces also hold transmembrane proteins in the membrane. There are 6 types of transmembrane proteins: anchoring proteins, recognition proteins, enzymes, receptor proteins, carrier proteins, channel proteins aka ion channels. Critical determinant of transmembrane ion movements (and thus ion concentrations) There are 165 positive ions inside the cell compared to 5 negative, how does this work: there are many proteins inside cells and they carry a slight negative charge. The atp driven na/k exchange pump establishes na and k concentration gradients that are critical to establishment of membrane potential: na and k both move uphill against their concentration gradients. How do concentrations get established: energy in atp used to drive na+ and k+ from low to high concentrations. Ions don"t like the lipid (cid:271)ilayer so they will not (cid:272)ross the pm unless through a water filled channel.
