Lecture 6: Channels and Transporters Flashcards
When the membrane potential is +52mV, what change in current occurs?
early inward Na+ current is missing
When the membrane potential is +65mV, what change in current occurs?
early inward Na+ current reverses to an outward flow
What technique provided the first direct evidence for single channels? Describe it
- Patch clamp technique
- voltage change activates channel openings
- glass pipet is sealed against cell membrane
- all current flows through electrode
In the patch-clamp technique, what do macroscopic and microscopic currents result from?
- Macroscopic - current flow through many channels
- Microscopic - current flow through a single channel
Ion channels open in a stochastic (___) manner
random
Depolarizing stimulus _____ the probability that the Na+ channel is opened when a K+ channel is experimentally blocked
increases
The sum of many _____ trials approximates the _____ of the _____ currents from the whole cell
- microscopic
- time course
- macroscopic
Which channels specifically inactivate? Which just close?
- Na+ inactivate
- K+ close
What forms the binding sites in the K+ channels? Whtt energetic role do they play?
- O atoms of 5 AA lining channel
- stabilize the energetically unfavorable shedding of H2O
Which atom, Na+ or K+ is larger? Which is effectively larger? Why? Which ion channel therefore has a smaller pore?
- K+ is larger
- Na+ is effectively larger - more water molecules which are more tightly bound
- K+ channel has smaller pore
How many types of Na+ channels exist?
One
How many types of K+ channels exist?
Multiple
What three characteristics differentiate K+ channels?
- low vs high voltage activation
- rate of activation (how quickly max conductance is reached)
- inactivation properties (fast, slow, do/don’t inactivate)
Describe activation of fast After Hyperpolarization. Which channel is involved?
- BK K+ channel
- activated by Ca2+ and depolarization; then rapid inactivation
- shortens AP by quickly repolarizing membrane
Describe activation of medium After Hyperpolarization. Which channel is involved?
- IK and SK K+ channels
- no inactivation
- slowly activated by Ca2+ entry; early interspike interval
Describe slow After Hyperpolarization
limits firing by an unknown channel
Ka is the A-type _____ potassium channel. It inactivates _____.
- voltage-sensitive
- rapidly
Kdr is the _____ potassium channel. It is ______ and inactivates _____ or _____.
- delayed rectifier
- voltage sensitive
- slowly
- does not inactivate
Kbk is the _____ (name), ___-activated, _____ potassium channel. It requires both _____ and _____ to be activated.
- big conductance
- Ca2+
- voltage-sensitive
- Ca2+ and depolarization
What are the 5 channel timings of APs?
- Na+ channels open
- Na+ channels inactivate; Ka and Kdr channels open
- Kbk channels open
- Ca2+ channels open
- other known and unknown K+ channels open
Which type of channel usually only allows one type of ion to pass through? Which usually allows multiple?
- Voltage-gated = 1
- Ligand-gated = multiple
Which K+ channel plays a + role in tumorigenic human mammary cells?
Kv1.4
So many genes encoding K+ channels allow them to differ in which three aspects?
Activation
Gating
Inactivation
Congenital stationary night blindness, familial hemiplegic migrane, and episodic ataxia type two are all due to mutations in ______ channels.
Voltage-gated Ca2+
Generalized epilepsy with febrile seizures is caused by a _____ channel defect
Na+
Benign familial neonatal convulsion is caused by a _____ channel mutation
K+
Teradotoxin (puffer fish), saxitoxin (red tide), Alpha- and beta-toxins (scorpion), and batrachotoxin (frogs) all affect ___ channels.
Na+
Dendrotoxin (wasps) and apamin (bees) affect ___ channels
K+
w-conotoxins and w-agatoxin affect ____ channels
Ca2+
Active ion transporters are _____ which create and maintain ion gradients using ____ as the energy source.
- membrane proteins
- ATP
Ion exchangers use the _____ as an energy source to exchange ions.
electrochemical gradients of co-transported ions
What is co-transport of ions?
2 or more ions/molecules move in the same direction across the membrane
