Chapter 3 -- voltage-dependent membrane permeability
Overview
First rapid and transient (tijdelijk) rise in Na (depolarization) than slow and long rise in
K repolarization and even hyperpolarization)
Ion currents across nerve cell membranes
Opening of Na channels is very important and therefore well researched.
The voltage-clamp method: control of the membrane potential and simultaneously
(gelijktijdig) measure the underlying permeability changes.
This provides information needed to define the ion permeability of the membrane at
any level of membrane potential (or voltage)
Voltage-clamp method: because it controls or
clamps membrane potential (or voltage) at any
level:
1. Internal electrode measure membrane
potential (or voltage) (Vm)
2. Voltage clamp compares membrane
potential (or voltage) with the desire
(command) potential (or voltage)
3. When Vm is different from common potential (or voltage), the clamp injects
current into the axon through a second electrode. This causes the Vm to
become the same as the command potential (or voltage)
4. Current flowing back into the axon and thus cross the membrane can be
measured here
Two types of voltage-dependent ion currents
Whether (of) neuronal membrane have voltage-
dependent permeabilities?
Membrane potential (or voltage) change negatively = hyperpolarization
Capacitive current is negative. Very little current flow of Na (Na channels are
closed)
Membrane potential (or voltage) change positively = depolarization
Capacitive current is first positive. Before Na channel open first a small
amount of Na flow out the cell
Then slowly rising negative (early inward current). Before Na channel open
first a small amount of Na flow out of the cell. When impulse is bigger than +52
mV no Na out of the cell anymore because of bigger permeability
Then become positive (late outward current). Large amount of
Na flow in the cell
Overview
First rapid and transient (tijdelijk) rise in Na (depolarization) than slow and long rise in
K repolarization and even hyperpolarization)
Ion currents across nerve cell membranes
Opening of Na channels is very important and therefore well researched.
The voltage-clamp method: control of the membrane potential and simultaneously
(gelijktijdig) measure the underlying permeability changes.
This provides information needed to define the ion permeability of the membrane at
any level of membrane potential (or voltage)
Voltage-clamp method: because it controls or
clamps membrane potential (or voltage) at any
level:
1. Internal electrode measure membrane
potential (or voltage) (Vm)
2. Voltage clamp compares membrane
potential (or voltage) with the desire
(command) potential (or voltage)
3. When Vm is different from common potential (or voltage), the clamp injects
current into the axon through a second electrode. This causes the Vm to
become the same as the command potential (or voltage)
4. Current flowing back into the axon and thus cross the membrane can be
measured here
Two types of voltage-dependent ion currents
Whether (of) neuronal membrane have voltage-
dependent permeabilities?
Membrane potential (or voltage) change negatively = hyperpolarization
Capacitive current is negative. Very little current flow of Na (Na channels are
closed)
Membrane potential (or voltage) change positively = depolarization
Capacitive current is first positive. Before Na channel open first a small
amount of Na flow out the cell
Then slowly rising negative (early inward current). Before Na channel open
first a small amount of Na flow out of the cell. When impulse is bigger than +52
mV no Na out of the cell anymore because of bigger permeability
Then become positive (late outward current). Large amount of
Na flow in the cell
