L2 - Bioelectricity Flashcards
How can Vm be measured
Similar method to a patch clamp
But electrode straight through the membrane
EC Na conc
150 mM
IC Na conc
15 mM
EC K conc
5 mM
IC K conc
150 mM
EC A- conc (anion)
0
IC A- conc
65 mM
How are all of these Na and K concentrations maintained
Na/K ATPase
Two blockers of the Na/K ATPase
Digoxin
Ouabain
When Na/K ATPase blocked what is the effect on Vm
Vm –> o mV
Why is the Na/K ATPase electrogenic
Net loss of one +ve charge
Contribution of K channels to the equilibrium potential
CONCENTRATION
Tends for K to move out, down gdt
POTENTIAL
Tends for K to move in, down gdt
Equilibrium potential
Two gradients equal no current flow
Nernst equation
(61.2/z) x log [x]i / [x]o
Nenst equation for K
61.2 x log (5/150)
= -90.1 mV
Contribution of Na channels to the equilibrium potential
CONCENTRATION
Tends for Na to move in, down gdt
POTENTIAL
Tends for Na to move out, down gdt
Equilibrium potential
Two gradients equal no current flow
Nernst for Na
61.2 x log (150/15)
= +61 mV
Goldman equation
Vm = (61.2/z) = log (pna[Na]o + pk[k]o) / (pna[Na]i + pk[k]i)
What does goldman equation determine
Membrane potential
Approximate Vm
-70 mV
Three movements of ions at Vm
Na (Ena)
K (Ek)
Na/K ATPase
If there is a change in Vm then what else must there be a change in
Change in the permeability to electrogenic transport
Describe the ion channels and movement of ions at a resting Vm
Many K channels are open
Many Na channels are closed
Vm –> Ek
What happens when threshold is reached
Voltage gated sodium channels open and the membrane potential approaches Na Nernst
Describe the significance of Na - Amino acid transport
Couple down hill transport of the Na gradient to the influx of amino acids
Cell is able to sustain a high level of Na transport whilst keeping the Vm close to resting
This is done by the opening of K channels in the membrane
