Talbot resting membrane potentials and membrane biophysics Flashcards
nernst equation
Ex (V) = [RT/(zF)] [ln [x]out/[x]in]]
Ex = equilibrium potential for ion x = a (theoretical) membrane potential (V or mV)
R = gas constant (8.31 J/°K mol)
T = temperature in °K (°C + 273)
z = valence (charge on ion)
F = Faraday’s constant (96,500 Coulombs/mol)
1 V = 1 J/C
Nernst equation is accurate for K+ movement at high extracellular [K+], but at low extracellular [K+], the nernst equation does not predict the membrane potential–> other ions influencing–> GHK takes these into account
Goldman-Hodgkin-Katz (GHK) Equation
Vm(mV)=61.5 log[(Pk[k]out) + (PNa[Na]out+ PCl[Cl]in]/[(Pk[K]in +PNa[Na]in+ PCL[CL]out]
if the gradient for a given ion and/or the permeability for an ion across the membrane changes, the membrane potential, Vm, changes.
Vm= a function of 2 parameters:
- permeability of the various ions
- concentration gradients of those ions across the membrane
For a typical cell, PK»_space;> PCl > PNa > 0
small changes in [K+] will have a greater effect on Vm than changes in [Cl-] and [Na+]
K+ becomes an important ion to measure because small changes in extracellular [K+] can cause large changes on Vm (normal [K+] extracellular=very low)–> larger effect on the cell.
hyperkalemia= serum [K+] 7mM==> severe, can cause cardiac arrest and death
Tetrodotoxin (TTX)
found in the skinand liver of puffer fish, blocks the fast voltage-gated Na+ channel of neurons and striated muscle.
K+ channels not affected–> cell remains hyperpolarized ==> no AP
Hodgkin loop
positive feedback system in biological systems (ex: giving birth, blood clotting)
Any stimulus that inducesa membrane depolarizationstarts the cycle; causingv.g. Na+ channels to open
As the Na+ channels open, the membrane is further depolarized, whichcontinue to induce more v.g. Na+ channels to open and the cyclecontinues
must have an outside mechanism to stop=the spontaneous inactivation of channels
