What can lead to an increase in membrane capictance of sodium (gNa+)
Increasing intracellular sodium woud increase gNa+
What can cause a focal depolarization of the plasma
Inward Ionic Current (+ charge moves in)
What is voltage clamping used for?
1. A method for measuring the “whole cell response” for a given class of ion channels.
2. A method of compensating for membrane capacitance so that membrane resistance can be directly measured in
current - voltage plots (V=IR).
How is Voltage Clamping done?
1. Apply a constant command
voltage (Vcom) across the plasma
2. Record the transmembrane current
(Itm) required to sustain the constant
What are the results of voltage clamping?
A current - voltage plot that
describes the channels under
Slope of the curve = Gx (whole cell conductance of ion x)
What do the downward and upward slopes of a current response plot represent in volatge clamping of fast Na+ channels.
The downward slope is due to the opening of Na+ channels and cell depolarization (inward Ionic current), An upward slope is the result of outward current.
What does voltage clamping an area with no voltage gated channels demonstrate?
What is the relationship between whole cell
and single channel conductance?
Gx = Nxo * Yx
Gx = conductance of all channel in a whole cell
Nxo = # open channels for a given ion
Yx = conductance of 1 open channel for that ion
What is single channel recording?
What are alpha and beta in terms of an ion channel's state?
How is the magnitude of a single channel current determined?
Sectioning off a segment of membrane "membrane patch" to measure magnitude if current and the amount of time channels are open and closed.
alpha = rate of a channel closing if open
beta = rate of a channel opening if closed
The magnitude of the
single channel current (i)
depends on the value of
the single channel
conductance (gamma) and the
force (Vm - Ex):
i = gamma (Vm - Ex)
What are 5 functional characterizations of ion channel?
Second messenger gated
What is the proposed model for "Fast Na+ channels"
opening and closing?
4 Motifs each containing 6 transmembrane subunits. The 4th subunit is the Activation Gate
Deactivation gate is a cytoplasmic loop between motifs 3 and 4
What are the 5 "moleulcar faimilies" of ion channels and an example of each?
1. Gap Junction Channels.
2. Depolarization - activated ion channels.
3. Inward Rectifying K+ channels.
4.Pentameric Ligand - gated channels.
5. Ionotropic Glutamate Receptors.
Describe gap junction ion channels
6 Connexins make a connexon, connexons of adjacet cells unite to form a gap juntion.
Very High Conductance
What's an example of a ligand gated channel (the one most focused on in calss)?
How does it function?
What are some other ligand gated channels?
Acetylcholine receptor (AChR)
AChR has 5 subunits and 2 binding sites for acetyl choline. If no ACh is bound, channel is closed. If two ACh bind, channel is open, allowing ions to flow in/out.
Other ligand gated channels include ATP receptors, GABA receptors, glycine receptors and glutamate receptors (he said don't worry about the glutamate receptors)