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37 Cards in this Set
- Front
- Back
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Concentration of Na+ in cells |
In plasma: 142 mM In intestinal fluid: 145 mM In intracellular fluid: 15mM |
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Gradient |
Transmembrane rate of change of concentration through membrane |
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Concentration of K+ in cells |
In plasma: 4.4 mM In interstial fluid: 4.5 mM In intracellular fluid: 120 mM |
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Concentration of Ca +2 in cell: |
extracellular: 1.2 mM intracellular: 10^-4 mM
VERY small amount due to 1. low Ca2+ permeability at rest 2. Ca2+ binds to many proteins and is no longer free |
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Concentration of Cl- in cell: |
Extracellular: 116 mM Intracellular: 20 mM
Current carrying ion for action potentials Major ion to preserve neutrality (because neg.) Blocks excitatory nerve action potential Ion exchange mech. for secretions epithelium |
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Cause of cystic fibrosis: |
no Cl- channels Cl- can't leave extracellular fluid, mucus builds up |
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Lipophilic non-electrolyte molecules and permeability: |
Water insoluble molecules, move between bilayer lipids
O2, CO2, N2, organic molecules (alcohols, ketones), anesthetics |
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Lipophobic non-electrolyte molecules and permeability: |
Water soluble, need pores and channels formed by integral proteins to get through membrane
--urea, glycerol, polar molecules with less than 5 carbon atoms |
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Transmembrane flux |
# molecules that pss thru membrane per time per area |
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Water transport through membrane |
Most permeable molecule, so rapid flux 10% thru lipids 90% through aquaporins |
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Pores vs channels |
Pore is not gated, whereas channel is, and not always open |
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Three types of channels |
Voltage gated: membrane polarization opens/closes gate
Chemically gated: endrogenous "agonists" (hormones/neurotransmitters) regulate secondary messenger cascade
Physical energy gated: secondary messenger system activated in various ways |
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Types of physical energy gated channels |
Pressure dependent (baroreceptors)
Shear stress dependent (cochlear/vestibular hair cells)
Light energy dependent (retinal cells) |
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Forces that govern simple diffusion |
1. concentration gradient 2. electrical potential gradient --can be caused by voltage being applied or separating ions with active transport |
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Fick's First Law of Diffusion |
Q is rate of mass mvt of uncharged particle
Q net = Q (outside to inside) - Q (inside to outside)
Q net=Px A Δ X
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Factors in Fick's First Law of Diffusion |
Q net=Px A Δ X
Px is permability constant; easy of momvenet in length/time
A is "effective cross sectional area"; area of lipid bilayer or area of channel x number of channels
Δ X is (Xi - Xo) or (Xo-Xi), depending on direction conc. gradient
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Determining permeability constant |
Px=DB/L
D=diffusion coeff, ease of mvt within cell membrane in length^2/time
B=partition coeff, ease of entry into cell or difference in force of attraction for diffusing molecules exerted by molecules in membrane
L=length of pathway or membrane thickness |
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Determining diffusion coeffient |
B= [Xi]'/[X]i = [X]o'/[X]
B>1 means incresed intramembrane conc. B<1 means decreased intramembrane conc. B=1 means intramembrane conc. gradient=transmembrane gradient |
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Flux |
Another way to describe movement; it is the amount of solute moved per unit time per unit cross sectional area perpendicular to flux direction
Jx=Qx/A or Jx=PxΔX
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Determining passive transport resulting from an applied voltage difference (in theory) |
Concentrations of ions assumed to be originally constant
ΔV=Vo-Vi, externally applied
Flux poportional to magnitude of gradient, permeability and conc. of ion
Pos. to neg. is direction by convention |
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Equation for passive transport resulting from applied voltage difference |
Jxnet = zPx [X][ΔV]
z=valence of ion
Total passive flux equation: Jxnet total = J x net chem + J x net electrical |
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Electrochemical potential T |
Sum of chemical concentration energy and electrical energy gradients in a typical cell |
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Vm |
Results from separation of positive and negative charges as permeable ions diffuse through a cell membrane |
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Vm at steady state |
Needs energy from ATP bonds due to ATP hydrolysis; this helps keep steady state rther than equillibrium potential by using Na/K pump
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GHK Equation |
Derived from Nerst equation because flux can be described as current;charges (ions) are moving
Equation tells us that current is a function of membrane potential and concentration difference across membrane |
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Application of GHK equation |
Ionic equillibrium electric potential across a planar lipid bilayer
Example: ion channels that only allow K+ through; intracellular compartment becomes negative as K+ moves out
Continues until Vk reached (-92.4 mV) |
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Vk |
With electrochemical gradient This is when the outward force generated by either chemical or electrical potential energy equals the opposite inwardly driving force
Equillibrium
Net flux=0, Ek=0
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Quantitative Expresion Equillibrium |
Use when Ik=0
Vk or Ek = RT/zF x 2.303 log ([K]i/[K]o)
*can have - in front of K/K |
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Resting Vm of cell |
-70 mV
When itotal=0 |
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GHK Constant Field Equation for Resting Potential |
Vm= -RT/F ln (Pk[K]i/Pk[K]o + PNa[Na]i/PNa[Na]o + PCl[Cl]o/PCl[Cl]i )
Cl is at equillibrium because no pumps, eliminate it |
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Myotonia congenita |
Cl- channel blocked, can't get inside cell to help repolarize
Causes a "myotonia" which is a prolongued contraction of muscles, retarded relaxation of clasped hand and abnormal walking gate |
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Finalized GHK Equation with Cl- eliminated |
Vm= -RT/F ln ( [K+]i/[K+]o + alpha[Na]i/alpha[Na]o )
Alpha=PNa/Pk |
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Effect of changing permeability on Vm |
Increase in Na+ permeability increases alpha and you get an increase in Vm magnitude
Vm can shift from -120 to -100 as PNa+ increases
As [K+]o increases, we get depolarization too (Vm closer to 0) due to reduced K+ electrochemical gradient and reduced Vm |
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Clinical implications of too much [K+]o |
Could get too many spontaneous, hyperexcitable depolarizations
Therefore lethal cardiac arrthymias/abnormal breathing patterns |
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Effect of Changes in Pk |
Decrease: would cause depolarization bc couldn't move down concentration gradient, less separation of positive and negative charges
Increase: would cause hyperpolarization because of greatr mvt of K+ down concentration gradient, causing more separation charges |
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Effect of Changes in PNa |
Decrease: would cause little change in resting Vm because contribution of iNa to Em small due to small PNa
Increase: would cause sig. depolarization because would lead to large iNa and separation of charges |
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Importance of alpha |
Absolute value Vm inversely proportional to alpha as alpha increases, membrane less polarized
to do so, open Na+ channels during action potential |
