What is the rest potential of the cell?
-65mV
What is the main role of the Na-K-ATPase?
Helps establish and maintain the high internal potassium and low internal sodium conc.
Name the 3 roles the electrochemical gradient plays?
1) Maintaining osmotic balance 2) Stable resting membrane potential 3) Excitable properties of muscle and nerve cells
What does the sodium gradient provide?
The energy that fuels the sodium-coupled transporters mediating the translocation of ions and substrates across the plasma membranes.
What is the role of the Na-K-ATPase in the kidneys?
Plays a primary role in driving the reabsorption of sodium and water
Why are enzymes so important in the body?
Essential for the maintenance of body fluid and electrolyte homeostasis
What 3 things can cause the gradients of ions in the cell to be abolished?
1) Cell death 2) Witholding glucose 3) Use of specific inhibitors
What is the concentration of sodium and potassium inside the cell?
Sodium: 10mM Potassium: 140nM
What is the concentration of sodium and potassium outside the cell?
Sodium: 140mM Potassium: 4mM
What is necessary to maintain the ion gradients?
Requires metabolic energy
What does the pump-leak hypothesis say?
It says that that actively removing sodium out of the cell is in harmony with the uptake of Potassium by passive leak of these ions in opposing directions.
What two gradients is the extrusion of sodium going against?
A chemical gradient and a potential gradient
Why is the extrusion of sodium against a potential gradient|?
Because a transmembrane potential also exists
What is the major source of energy for active cation transport for most cells (ie. muscles and nerve)?
These perform oxidative metabolism that serves as the major source
Define the term "cation"?
An ion that has a positive charge and characteristically moving toward the negative electrode in electrolysis
Define "oxidative metabolism"?
The combination of organic substances with oxygen in order to produce energy.
How does red blood cells inhibit active cation transport?
Absence of oxidative metabolism. Inhibitors of glycolysis still inhibits active cation transport.
The effect of glycoside (ouabain) on the Na-K-ATPase?
Inhibits even with sodium and potassium present.
The effect of magnesium on the Na-K-ATPase?
Co-factor. Not needed for transport but increases the activity
What is the optimum pH for the cell?
pH 7-7.5
The transport system of Na-K-ATPase?
Pumps 3 sodium out of the cell and brings back 2 potassium (using ATP when pumping out the sodium)
How to work out the Km?
Km=Vmax/2
Describe the 5 different stages of Na-K-ATPase?
1) 3 sodium ions bind. 2) Phosphate added onto the protein. 3) Conformational change. Sodium losses its affinity. 4) Potassium has a high affinity for this new conformational (2 bind) 5) Phosphate removed. Conformational change
Describe the 7 steps for the Na-K-ATPase (based on the albers-prost scheme)
1. Binding of 3 sodium ions 2. Binding of ATP, phosphorylation of aspartate, 3. Confirmational change (E1->E2) 4. Dissociation of sodium, binding of potassium. 5. Hydrolysis of aspartyl phosphate 6. Confirmational change (E2->E1) 7. Dissociation of K
What activity is an integral part of the enzyme that promotes the Na-K-ATPase?
The K-stimulated phosphatase activity
Define "phosphatase"?
Splitting of the phosphate
Define "ATPase"?
Splitting of the ATP
What two things can be used to show the operation of the Na-K-ATPase?
1. Reconstituted enzyme. 2. Use of radiotracer
Name the 5 different modes of the Na-K-ATPase pump?
1. Normal mode (sodium/potassium exchange) 2. Reverse mode 3. Na-Na exchange (1:1) 4. Uncoupled sodium efflux 5. K-K exchange (1:1)
Define the term "uncoupled sodium efflux" when describing a mode of the sodium pump?
Sodium and potassium only present on the inside. Therefore, there is no sodium present outside the cell so when the pump excretes potassium it is cannot bring sodium in and will be locked facing the outside of the cell.
Define the role the sodium pump does?
Helps maintain the normal transmembrane electrochemical gradients of Na and K in association with the membrane permeability properties. Through this, maintain a stable membrane potential.
Name the two types of sodium pumps?
1. Sodium and potassium exchanger. 2. Sodium and amino acid exchanger (using the enzyme of the sodium to transport the aa into the cell)
What family of ATPase is Na,K-ATPase a member of?
P-type ATPase
What is the P-type ATPase made up of?
Alpha, beta, gamma and oligosaccharides
Describe the catalytic subunit of a pump? What part of the P-type ATPase is this particular subunit
It possesses binding sites for lots of ions such as sodium and potassium. Intrinsic ATPase activity. 4 isoforms: a1->4. The alpha subunit
Describe the regulatory subunit of a pump? The 3 roles it does? What part of the P-type ATPase is this particular subunit
Three isoforms (B1->3) Crucially required for full enzyme activity but also for enzyme assembly, intracellular transport and stability of the alpha subunit. beta subunit
Describe the small auxiliary protein of the pump? What subunit is it?
Single spanning membrane peptide. Gamma subunit
How many isoforms of Na-K-ATPase is expressed in the kidney?
1 isoform
How many isoforms of Na-K-ATPase is expressed in the brain?
2 isoforms
How many isoforms are there for the alpha subunit of Na-K-ATPase? What is the role of each
alpha 1: ubiquitous expression (house keeping gene) Alpha 2: Excitable tissues alpha 3: Excitable tissues alpha 4: Only expressed spermatozoa
Beta subunits of Na-K-ATPase function in skeletal muscle
beta 1: oxidative properties beta 2: contractile properties
How many different isoforms of beta sunlit of Na-K-ATPase?
2. Beta 1 and beta 2