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the membrane proteins that create and maintain ion gradients
active transporters
give rise to selective ion permeability change
ion channels
ion channels
membrane proteins that contain specialized structure called a pore that permits particular ions to cross the neuronal membrane
membrane proteins that produce and maintain ion concentration gradients
active transporters
most important active transporter
sodium pump
sodium pump
hydrolyzes ATP to regulate the intracellular concentrations of both sodium and postassium
how are active transporters and ion channels complementary
transporters create concentration gradients that help drive ion fluxes through open ion channels thus generating electrical signals
properties of channels found by voltage clamp experiments
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
what did the patch clamp experiments allow
to test directly hodgkin and huxleys proposals about the characteristics of ion channels
microscopic currents
currents flowing through single channels
macrscopic currents
flowing through large number of channels distributed over a much more extensive region of surface membrane
basis of patch clamp experiments
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
cell attached patch clamp recording method
when the pipette is attached to the membrane
whole cell recording
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
inside out path recording configuration
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
outside out patch recording configuration
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
tetrodotoxin
blocks the macroscopic Na+ current also blocks microscopic Na+ currents
ion selectivity
able to discriminate between sodium and potassium (can tell between different ions)
voltage gated
opening is influenced by membrane potential
voltage sensor
detects the potential across the membrane
inactivation
prevention of channel to stay open
what causes sodium channel inactivation
depolarization
both opens and closes
major physiological ions that have voltage gated channels
sodium
potassium
calcium
chlorine
How many genes do humans have for voltage gated sodium channels
10
rapid inactivation and some channels that do not inactivate
how many genes are there in humans for calcium voltage gated channels
16
what types of processes do calcium voltage gated channels activate
release of neurotransmitters
what types of drugs treat anxiety disorders
drugs that block voltage gated calcium channels
how many potassium channel genes do humans have
nearly 100
what channels influence the duration and rate of an action potential
potassium channel closing
what do voltage gated chlorine channels do
they control excitability, contribute to resting membrane potential and regulate cell volume