Neurobiology

active transporters

ion channels

membrane proteins that contain specialized structure called a pore that permits particular ions to cross the neuronal membrane

active transporters

sodium pump

hydrolyzes ATP to regulate the intracellular concentrations of both sodium and postassium

transporters create concentration gradients that help drive ion fluxes through open ion channels thus generating electrical signals

• channels must allow ions to move across the membrane at high rates
• channels had to make use of electrons chemical gradients
• different channel types had to be capable of discriminating between sodium and potassium
• must be able to sense voltage drops

to test directly hodgkin and huxleys proposals about the characteristics of ion channels

currents flowing through single channels

flowing through large number of channels distributed over a much more extensive region of surface membrane

• a glass pipette with a very small opening used to make tight contact with a tiny area
• after using small amount of suction to the back of the pipette
• this causes a tight seal that do not allow ions to pass through
• thus all ions that pass through ion channel must go through the pipette

when the pipette is attached to the membrane

• when the membrane patch within pipette is disrupted by briefly applying strong suction and interior of pipette becomes continuous with the cell cytoplasm
• allows measurmetns of electrical potential and current from entire cell

• retract a pipette that is in the cell attached configuratin causes small vesical of membrane to remain attached to pipette
• exposing tip of pipette to air allows vesicle to open to yield small path of membrane with its former intracellular suface exposed
• allows to change intracellular

• if pipette is retracted while in whole cell confiuration a membrane patch produced has its extracellular surface exposed
• allows study of how channel activity is influenced by extracellular chemical signals

blocks the macroscopic Na+ current also blocks microscopic Na+ currents

able to discriminate between sodium and potassium (can tell between different ions)

opening is influenced by membrane potential

detects the potential across the membrane

prevention of channel to stay open

• depolarization
• both opens and closes

• sodium
• potassium
• calcium
• chlorine

• 10
• rapid inactivation and some channels that do not inactivate

16

release of neurotransmitters

drugs that block voltage gated calcium channels

nearly 100

potassium channel closing

they control excitability, contribute to resting membrane potential and regulate cell volume