BIOL 2480 - L4

How do we know? Patch-clamp can quantify

ion flow through a single channel.

What are the 4 types of cell recordings?

Cell-attached recording

Whole-cell recording

Inside-out recording

Outside-out recording

Cell-attached recording is the easiest way, and is done by the pipette being stuck on the mb, suctioning to isolate

1 channel of the cell, getting the whole cell response

Whole-cell recording measures the

cytoplasm

Inside-out recording measures

inside channel, and also can ass into the cell thru this process

Outside-out recording measures

outside channel

Ion channel characteristics: Ion flux through the channel is

passive, no energy is required once the channel is open

Ion channel characteristics: Channels are

selective, some let 1 ion thru (K, Na, ect)

Ion channel characteristics: Driving force depends on

•electrical potential and concentration difference. (change in charge, determines the direction of ion flow)

Ion channel characteristics: Opening and closing involves change in

conformation (shape)

Ion channel characteristics: Some channels act as

rectifiers, has a preferred direction (inward or outward)

rectifiers has an

activation gate, an extra part of the channel that swings open/close

Voltage-gated channels: Regulated by change in voltage at

voltage sensor

Voltage-gated channels: Inactivation by:

Prolonged voltage

Calcium binding

Dephosphorylation

Na channel starts closed, then flap opens, opening channel and depolarization activates, then with prolonged depolarization, channel is

deactivated and closes again

Ligand-gating - Ligands must bind to

receptor, can bind in/out of cell

NT receptor: NT acts as a

ligand

Ca-activated K channel, Ca acts as a

ligand, binds to receptor to allow K to flow in

cyclic nucleotide gated channels, cAMP, as a intercellular signal messenger, binds

as a ligand and opens as a channel

•Mechanical gating - Physical force causes

conformational change

-saxitoxin (eating oysters) causes blocking of

Na channels and voltage gated Na channels

batrachotoxin (licking a frog) stops deactivation of

Na channels

-Get a disease

•Channelopathies, disruptions in

channels, can cause severe migraines, it is an inherited disease and is not common

How do voltage-gated channels work? 2 membrane-spanning domains form

pore, (also known as a toansmembrane domain)

Changes in voltage cause

conformational change

One "pore domain" has loop for

selectivity, (only small ions, size, charge on ion itself)

K+ channels

Very diverse in

structure and function

Types of K+ channels

-Onset

-Offset

-Inward rectifier

-Calcium activated

Onset and Offset channels are important in

figuring out timing

-Onset K channels only affected by the

beginning of stimulus

Offset K channels ignore the

initial charge, only when voltage stops, it fires (closes)

Inward rectifier (can also be outward) only let current flow

into the cell

Ca activated - inside a cell that uses

Ca as a messenger, the more Ca, the longer the response

•If all these ions are flowing around, how do they maintain a stable concentration?

Answer:

-active transporters.

•ATPase pumps

•Ion exchangers

ATPase pumps, Best known is

Na+/K+ pump

Removal of Na+ is DIRECTLY linked to

addition of K+

Na+/K+ Pump is

electrogenic, generates electricity through movement of ions

Na+/K+ pump Inhibited by

ouabain (can test if it is involved in a cell/pathway by using)

Na+/K+ pump steps 1) 3 Na bind to

receptor from inside the cell

Na+/K+ pump steps 2) receptor is phosphorylated to

change conformation, opening channel to outside of cell

Na+/K+ pump steps 3) Na is brought out and

2 K binds in

Na+/K+ pump steps 4) dephosphorylation occurs, causing a confirmation change,

causing K to be released inside cell

Ion exchangers

•Cotransporters

•Antitransporters

•Cotransporters

brings in an ion, both in the same direction

•Antitransporters

goes in different directions, 1 in and 1 out

Na/Ca exchanger

antitransport, 2 Na in, 1 Ca out

Na/H exchanger

antitransporter, used to keep electrical charges the same, good way to lower pH in a cell

examples of cotransporters

- Na/K/Cl

- K/Cl

- Na/NT