Lec 03 Flashcards
Icf and Ecf are in
Electrical and chemical disequilibrium
-Many of the solutes in body are ions (have electrical charge on them)
-Unevenly distributed across cell membrane (selective permeability based on ion channels and transporters)
Potassium conc in Icf vs Ecd
140 vs 4 mM
Sodium conc in Icf vs Ecd
15 vs 145 mM
Calcium conc in Icf vs Ecd
0.001 vs 1.8
Chloride conc in Icf vs Ecd
4 vs 115 mM
Most important reason of K disequilibrium
Potassium leak channels
Resting Membrane Potential
Net charge of ICF and ECF at rest
Result of unequal distribution of ions
All living cells have resting membrane potential
RMP IS USUALLY NEGATIVE
most important factor: K LEAK CHANNELS
Measuring potential difference
Outside is set to 0
Inside cell relative to outside is measured
Equilibrium potential
Electrical gradient exactly opposes concentration gradient so there is no net movement of ions
Permeable ions will move down the electrochemical gradient until ———
V(m)=E(x)
Equilibrium
Nernst Equation definition
If membrane was only permeable to one type of ion, membrane potential would be equal to nernst equation
Nernst Equation
E(ion)=61/z*log(ion(out)/ion(in))
Potassium ion electrochemical gradient
1- K concentration gradient drives k out of the cell
2- excess negative charge pulls k back
If E(k) is 80mv and V(m)=-120mv
Stronger electrical gradient
Greater tendency of potassium to stay in
NET INWARD FLOW
If E(k) is 80mv and V(m)=-94mv
Equilibrium potential
NO NET ION FLOW
If E(k) is 80mv and V(m)=-80mv
Stronger chemical gradient
Greater potassium tendency to leave
NET OUTWARD FLOW
GHK equation definition
Predict membrane potential that results from contribution of all ions across membrane
GHK equation two factors
1- concentration gradient
2- relative membrane permeability
Resting membrane is close to E(k)
1- cells are 40 times more permeable to k than Na
2- k leak channels
3- K is primary contributor to RMP
K eq potential
-90 mV
Primary modulator of ion permeability
Ion channels
V(m)=-80mV why?
1- k leak channels
2- na/k pump
3- negative charge phosphate and protein
When potential is getiing more negative
Hyper polarization
Membrane potential is getting more positive
Depolarization
