West Material Flashcards
Phospholipid bilayer acts as what in circuit of cell?
Capacitor.
Cap. is proportional to Area.
Cap is inversely proportional to distance
At what rate do ion channels conduct ions across the plasma membrane?
“at a rate near the diffusion limit across the plasma membrane
Do ions move faster through ion channels or carriers?
- ion channels
- (10^6-10^8 ions/sec)
- current equivalent (10^-12-10^-10 amps (1-100 pA))
Na-K exchanger
* 300 Na+, 200 k+ /sec
* Current equivalent of 1.5x10^-17 A.
Define Nernst Potential
-Calculated potential at which the concentration of an ion inside and outside a cell is in equilibrium.
-Driving force due to charge separation is exactly equal and opposite to chemical force due to concentration gradient.
-Potential at which the net current of an ion is zero.
Nernst Potential Equation
E_x = RT/zF * ln([x]_out / [x]_in)
F = Faradays Constant (F = 96485.3321233100184 C mol−1)
R = gas constant (R = 8.31446261815324 J K−1 mol−1,)
z = Valence
T = Temperature (in Kelvin)
Nernst Table
Sodium Concentrations outside and inside cell
[Na+]_out = 145
[Na+]_in = 18
Results in a Nernst Potential of +56
Potassium Concentrations without and within cell
[K+]_out = 3
[K+]_in = 135
Results in a Nernst Potential of -102
Chlorine Concentrations within and without a cell
[Cl-]_out = 120
[Cl-]_in = 7
Results in a Nernst Potential of -76
Calcium Concentrations within and without a cell
[Ca2+]_out = 1.2
[Ca2+]_in = .1uM
Results in a Nernst Potential of +125
Na-K Pump
pumps 3 Na+ out of cell, pumps 2 K+ into cell
Goldman-Hodgkin-Katz Voltage Equation
notice Cl is inverted because of it’s valence
58*log is replacing RT/F ln()
Choroid Plexus
Ion Channels as resistors
Full Neuronal Circuit
Time Constant Equation
Tau = RmCm
Rm = membrane Resistance
Cm = membrane Capictance
REMEMBER: SMALLER == FASTER
Length Constant
Lambda = sqrt(Rm/Ra)
Rm = membrane Resitance
Ra (Ri) = axial Resistance
REMEMBER: LARGER == LESS DEGRADATION
Action Potential related changes in conductances
Sequential increases in Na+ and K+ conductances
Current Equation for specific ion
I_x = g_x * (V_m - E_x)
E_x = equilibrium potential. This is empirically determied by reversal potential
How to Draw IV Curves
Current = 0 @ Ex. Draw a straight dotted line with an x-intercept @ Ex. Channel is closed prior to it opening, when it’s opening voltage is reached, it slowly approaches the dotted line. When channel fully open, it joins the line and follows it.
Positive Current flows in which directions
FOR DR. WEST (voltage clamping): positive current is out of the cell. Negative current is cations flowing into the cell
Structural Components of Voltage Gated Ion Channels
- Transmembrane, extra- & intra-cellular domains
- Gates
- Pore and Selectivity Filter
- Voltage Sensor
How many domains in alpha subunits of Voltage-gated sodium channel have? How many transmembrane segments does each domain have?
4 homologous domains.
6 transmembrane segments
Which alpha subunit is the primary voltage sensor for Sodium gated channel?
S4
contains multiple charged amino acids
