lecture 5

lecture 5 - Ion channels underlie action potentials...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Ion channels underlie action potentials Predictions of the nature of channels from Hodgkin and Huxley. Different channels for Na+ and K+. Channels must be gated by the membrane potential. Because conductances are large, channels must be able to pass ions at high rate. Problem-Voltage clamping cannot look at individual channels, they look at a whole bunch of channels at once and measure the aggregate current Fowing through them. What does an individual channel look like? How does it work? Solution: Patch Clamping
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Patch clamp method Neher and Sakmann cell-attached recording
Background image of page 2
Patch Clamp • Allows one to look at currents fowing through a single channel. • Pipette with small opening makes a tight seal with the membrane. • Currents are ampliFed and measured • Can be adapted to do whole cell recordings, inside out recordings or outside out recordings.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The Patch Clamp Method measures ion fow through a single channel
Background image of page 4
pipette is continuous with cytoplasm, can measure potentials and currents from the entire cell, also can introduce things into the cytoplasm makes it easy to introduce things to the cytoplasmic side of the channel makes it easy to introduce things to the extracellular side of the channel
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
"for their discoveries concerning the function of single ion channels in cells" The Nobel Prize in Physiology or Medicine (1991) Erwin Neher Bert Sakmann 1991 Nobel prize in physiology or medicine
Background image of page 6
Patch clamping Na+ channels Block K+ channels with Cs+ (can also use TEA). Brief depolarizations cause small inward currents that disappear right away. Each inward current is the opening of one Na+ channel. About 1-2 pA of current = thousands of ions/msecond. Stochastic opening, biased at the beginning of a pulse. Probability of opening varies with membrane potential. If you remove Na+ from medium, do not see currents. Tetrodotoxin blocks currents.
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Measurements of Ionic Currents Flowing through Single Na+ Channels Small inward currents Open at beginning of pulse Close quickly
Background image of page 8
Measurements of Ionic Currents Flowing through Single Na+ Channels summed current of many channels looks like macroscopic currents seen by voltage clamping probability of opening increases as a function of membrane potential
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 02/28/2011.

Page1 / 49

lecture 5 - Ion channels underlie action potentials...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online