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ISCI 2A18 (9)

Carolyn Eyles (9)

Lecture 3

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

by OneClass168541

2 pages116 viewsFall 2014

School

McMaster University

Department

Integrated Science

Course Code

ISCI 2A18

Professor

Carolyn Eyles

Lecture

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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

 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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