Membrane Potential (Al Medhi) Flashcards
Functions of ionic concentration gradient
- Action potential
- Pace maker activity (heart/gut CYCLIC action potential)
- Signaling
- Cell volume homeostasis
- pH homeostasis
Action potential
excitable cell function resulting from rapid change in membrane potential
pace maker activity
sequential opening of ion channels at particular membrane potentials
signaling
dependent in change in membrane potential (Ca2+ etc)
Cell volume homeostasis
influx/efflux of ions determines water homeostasis
(aquaporins follow concentration gradient)
pH homeostasis
concentration of hydrogen ions
many enzymes require a specific pH to act
Na+
lower inside
higher outside
K+
higher inside
lower outside
Cl-
lower inside
higher outside
HCO3-
lower inside
higher outside
Ca2+
higher inside
lower outside
Active Transporters
create concentration AND electrical gradient
electronegative charge INSIDE cell
more positive charge is exiting
Na+-K+-ATPase
pump two K+ IN
pump 3 Na+ OUT
What determines membrane resting potential?
Ion channels
Uncharged molecules move across the membrane by:
passive transporters
GLUT1 uses […] to drive glucose into the cell
The concentration gradient
*glucose is UNCHARGED
Energy sources for charged molecules
concentration gradient
electrical charge gradient
Nerst Equation
Vm
resting membrane potential/equilibrium potential
Vm for specific ions
The Goldman Equation
describes the reversal potential across a membrane
(membrane potential at which there is no net flow of ions)
used for REAL cells → more than one ion channel is open
Current direction
direction of movement of positive charge
Ligand gated channels
follow concentration gradient
4 primary voltage gated channels
Na+
K+
Cl-
Ca2+
What amino acids sense voltage?
Lysine and arginine
positively charged
mechanism of voltage-dependent gating
negative electrical field → inward pull → closes channel
depolarization (cell gets more positive) → outward push → conformational change → pore opens → hydrophobic loop blocks pore → inactivation (physically open but blocked: refractory period)
action potential duration
should be about 1 ms
whole thing about 2 ms, including hyperpolarization and return to resting potential
mechanism of inward rectification
hyperpolarization → inward rectifying potassium channels are opened (Kir)
- voltage current relationship is linear
- channel opens briefly, potassium exits
- from -25 to 25 mv, no current
- >+50 mV, a very low slope outward rectifying current
Outward non-rectification
- potassium pore is negatively charged
- in positive voltages, positive ions try to escape cell
- larger positively charged molecules (magnesium and polyamines) are pushed into potassium channels and block them
- → potassium is prevented from leaving cell
Lidocaine
lidocaine: voltage-gate sodium channel blocker
local anesthetic
