Lecture 7 Outline Flashcards
(37 cards)
Electrochemical gradients are dependent on both…
concentration & charge
- under physiological conditions, electrochemical gradients are established for K+, Na+ & Cl-
Membrane potential vs RMP
MP of a cell: due to electrical gradient across a cell membrane - unequal distribution of charges (ions) - established by ATPase transporters measured in mV (millivolts) not constant: - MP can change due to movement of ions
RMP
- special case of MP, where there is steady-state balance b/t active transport & leakage of ions
- for most cells, RMP b/t -20mV & -90mV
Define Depolarization
more +
- towards 0
Define Hyperpolarization
even more -
- even more away from 0
Define repolarization
more -
- away from 0
Equilibrium potential definition
the membrane potential that exactly opposes the steady state electrochemical gradient for an ion
follows the convention: “inside with respect to outside”
Nernst equation
Eion=61/z x log ([ion]out/[ion]in)
Example normal physiological conditions for equilibrium potential
K+ -90mV
Na+ +60mV
Ca2+ +122mV
Cl- -81mV
Independence
The equilibrium potential for each ion is independent of the concentration of the other ions
- ex: the equilibrium potential for K+ has NO EFFECT on the equilibrium potential for Na+ or Cl-
RMP Goldman Equation
RMP (in mV) = 61 log (Pk [K+]out + PNa [Na+]out + PCl [Cl-]in/ Pk [K+]in + PNa [Na+]in + PCl[Cl-]out)
predicts RMP considering 2 factors:
- relative permeability of Na+, K+, & Cl-
- the concentrations inside & outside the cell
Example normal physiological conditions of RMP
Normal, healthy is -78mV RMP
*the ion that has the greatest permeability contributes the most towards determining what the RMP will be
Example kidney failure Equilibrium potential
elevated [K+out]
hyperkalemic (10 mM K+)
= -67mV (depolarization)
High Na+ permeability
PNa=10 000
RMP = +58mV (VERY positive)
What would cause this?
the opening of VG Na+ channels for ex
Movement of ions changes MP: K+
relative concentration inside: high
EP = -90mV
direction of movement when ion channels out: OUT
Movement of ions changes MP: Na+
relative concentration inside: low
EP = +60mV
direction of movement when ion channels out: IN
Movement of ions changes MP: Ca2+
relative concentration inside: low
EP = +122mV
direction of movement when ion channels out: IN
Movement of ions changes MP: Cl-
relative concentration inside: low
EP = -81mV
direction of movement when ion channels out: IN
Why is the cell membrane an effective insulator?
it is able to keep charges separated from each other
Define electrochemical gradient
combo of an electrical gradient & chemical gradient
- ions subjected to an electrochemical gradient will move
Define electrical gradient
ex: inside the cell there is more (-) & outside more (+)
Define chemical gradient
ex: more of the green (-)’s inside than outside
- vice versa with the red (+)’s
Describe how to measure MP
convention is “inside with respect to outside”
Ex: if a cell has a RMP of -70 mV it is -70mv “inside with respect to outside”
- take a sharp electrode & poke it inside the neurons & measure the MP “inside with respect to outside”
Describe the hypothetical cell with a K+ pump (Active transport) and leakage channels
concentration of K+ maintained over time
system is at STEADY STATE where the rate of leakage thru leakage channels is exactly balanced by active transport
NOT equilibrium b/c it requires constant energy
Now imagine that the K+ pump (active transport) in the hypothetical cell is stopped (add a poison for ex)
K+ would eventually leak out until inside & outside are at an equilibrium
