Lecture 3: Voltage Clamps and membrane potential Flashcards
How would you record membrane potential?
Micropipet with KCl and Patch pippet.
Describe the micropipet recording.
Take a fine tip of a glass pipet and pierce the cell of interest. The pipet is filled with KCl because of their matching diffusion rate so doesn’t effect the reading. Place another point in the ground (outside of cell) Measures inside and outside of cell.
Describe cell patching.
Pipet with wider diameter, create suction between the cell membrane and the pipet. All ions will flow into the pipet.
Whole cell patch: strong suction breaks off the cell and the pipet receives information about the whole cell. from the cytoplasm.
What is the resting membrane potential?
The voltage difference between inside and outside of the cell, around -70mV.
Describe ion pumps.
A specific group of ions that pump from one side of the plasma membrane to the other. Uses ATP hydrolysis for energy. Adds a phosphate to the protein.
Force ions to move against their electrochemical gradient.
Extracellular -> Na more abundant
Intracellular-> K is more abundant.
Describe ion channels.
Contains small pore that allows specific ions to pass.
How do you find out equilibrium potentials?
Nernst Equation
Ex= 58.mV/z log [x]out/[x]in
How do you find conductance weighted average?
Vm=gkEk+gnaEna/gk+gna
What is the conducted weighted average?
Use when there are multiple ions contributing to the membrane potential.
How do you measure leak conductance?
(Vcommand - Erest) x gleak = Ileak
How do you now when equilibrium is reached?
No more voltage or current changes. Ions are stable.
When chemical driving force = voltage across the membrane. (Ek = Vm).
How do you measure the RC time constant?
Capacitor does not react quickly to voltage step, unlike the resistor. Therefore, there is a certain amount of time the capacitor will take to change its state.
Tau(sec) = RΩ x C(F)
Voltage change across the capacitor plates
As capacitor charges, VR and I decay. Resistance decays because no more current. Capacitor is charged.
Vc=Vtotal(1-e -t/RC)
Vr= Vtotal(1-e -t/RC)
How do you find the voltage of the capacitor in a parallel circuit with two batteries?
Conducted weighted average of the two batteries
Vc=Vaga + Vbgb/ga+gb
