Proteins and bioelectricity Flashcards
What are the main ionic components of the intracellular fluid?
- High phosphate
- K+
- Low Na+
- Low Cl-
What are the main ionic components of the extracellular fluid?
- High Na+
- High Cl-
- Low phosphate
What are the 3 main types of membrane protein
- Carrier
- Channel
- Pump
List the order of speed of turnover of these proteins
Fastest- channel
carrier
Slowest- pump
What technique measures the activity of ion channels?
Patch-clamp technique
What are the 3 types of carrier?
Uniporter
Symporter
Antiporter
What is the structure of a bacterial K+ channel?
Tetramer
4 identical subunits
Arranged symmetrically around a central ion conducting pore
What are 4 characteristics of the Na+/K+ ATPase
- It is ubiquitous
- Pumps 3Na+ out for every 2K+ in
- Electrogenic (charge generating)
- tetramer structure- 2 alpha subunits, 2 beta subunits
- Maintains low intracellular Na+
- Critical for maintaining the resting membrane potential
What are the components of:
I=N.Po.g.(Vm-Ei)
I- current N- number of channels Po- open probability of channels g- single channel conductance Vm- membrane potential Ei- equilibrium potential for the ion
How do you regulate the current?
Change the no. of channels- membrane shuttling
Change the open probability of a channel- phosphorylation, Ca2=, G proteins etc.
Change the Vm by activating or inhibiting other channels
How do you measure membrane potential?
Using glass micro-electrodes
Measures potential difference between inside and outside of cell
Vm=Vi-Vo
*Voltage sensitive fluorescent dyes
What are the concentrations of K+,Na+ and A- in the intracellular and extracellular fluid?
Na+- IC= 15mM, EC= 150mM
K+- IC=150mM, EC=5nM
A- IC=65mM, EC=0
What is the Nernst potential for an ion?
When all channels for a particular ion are open, and there is no net movement of the ion= Nernst potential for an ion
What is the Goldmann equation, and how is it different to the Nernst potenial?
Vm= RT/ZF x log pK[K+]o+pNa[Na+]o
/ pK[K+]i+pNa[Na+]i
What causes a change in Vm?
A change in the permeability of electrogenic transporters
How do you calculate the Nernst potential
Eion= RT/ZF x log [ion]out
/ [ion]in
Why is it important that [Na+]i to be low?
1.Counter-current multiplication (in the thick ascending limb)- reabsorption of NaCl into blood
Activity of NKCC2 depends on inwards Na gradient
*If this is compromised- diuresis
2.Maintaining resting membrane potential in cells
*If [Na]i increases- problems with propagation of action potentials
How is [Na+]i controlled?
Na/K ATPase
What happens when ATP phosphorylates the pump?
Conformational change arises, faces outside- Na+ released outside the cell
What limits the rate of this pump?
[K]o, [Na]i and ATP
What is the concentration of calcium in the intracellular and extracellular fluid?
Extracellular= 1million nM Intracellular= 100nM
What are the 2 classes of calcium store channels?
- IP3 receptor channels
2. Ryanodine receptors- low concentration of ryanodine activates the receptor
What are the 4 types of calcium channel?
- Voltage gated Ca2+
- Receptor activated Ca2+ channels- NMDA etc
- Mechanically operated Ca2+ channels
- Store operated Ca2+ channels
Why is Ca2+ regulation so important?
Ca2+ is important in second messenger signalling
How is [Ca2+]i kept low?
- Na/Ca exchanger
2. Ca2+ ATPases
How does the Na/Ca exchanger transport Ca against its concentration gradient?
Uses energy stored in the electrochemical gradient of Na+ by allowing 3Na+ to flown down its gradient in exchange for 1 Ca
What are the 2 main types of Ca2+ ATPase
PMCA- Ca2+ out of the cell
SERCA- Ca2+ into sarcoplasmic reticulum
