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Lecture 3

ISCI 2A18 Lecture Notes - Lecture 3: Serca, Nicotine, Nicotinic Acetylcholine ReceptorPremium

2 pages100 viewsFall 2014

Department
Integrated Science
Course Code
ISCI 2A18
Professor
Carolyn Eyles
Lecture
3

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Resting Membrane Potential and Channelology
September 16, 2014
Cells selectively and dynamically control the movement of ions to create/shape:
Resting membrane potential (vrest) separation of charge creates an
electric potential difference across membrane, vrest gives magnitude and sign
of this difference when the cell is at rest (not signaling), inside of cell is ve
with respect to outside, order of magnitude generally 10s of millivolts
Generator (sensory) potential seen in cells that may or may not be
neurons, ex. photoreceptors
Synaptic potential
Action potential
To set up a potential difference, the barrier must have selective permeability to
charged particles. For neurons, the relevant charged particles are Na+, K+, and Cl-
ions, which are controlled by transporters and ion channels.
Transporters:
Selective
Actively transport ions across membrane
Pump against concentration gradient
Driven by ATP, concentration gradient (co-/anti-transport), pH
Speed limited by protein conformational change (~103-106 ions/sec)
Ion Channels:
Selective
Open/closed states, with regulated state transitions
May spontaneously convert to inactivated state
Ions passively diffuse no flux against concentration gradient
Speed limited by diffusion (as high as ~108 ions/sec)
Transporters in Neurons Na-K-ATPase (enzyme):
Critical for all mammalian cells
Maintains cell volume generally, and volume in neurons uses ~20-30% of
all ATP produced
Pumps Na out of cell and K into cell can pump out K substitutes, but does
not pump in Na substitutes does not pump Na in, but can pump other cations
in
A P-type ATPase as is SERCA (Ca-ATPase of the endo-/sarco-plasmic
reticulum)
Looks like it was designed to remove Na from the cell after action potential
2 subunits: alpha has binding sites for Na+, K+, and ATP and is analogous to
SERCA, beta appears to be required for K+ anti-transport
Auxiliary protein may also associate with alpha-beta complex
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