nervous system and cardiac ion channels

Question 1

what is the function of L-type calcium channels?
> in the action potential

Answer 1

these are voltage gated channels responsible for the plateau of an AP (calcium influx)

also help with cardiac contraction

Question 2

how can ion channels be controlled by PTM?

Question wording??

Answer 2

phosphorylation
voltage changes
ligand binding
pharcological intervention

all influence space and time regulation of ion channel proteins

Question 3

how does adrenaline influence heart behavior?

Answer 3

increase heart rate and force of contraction

if have LQTS then fatal ventricular tachycardia can happen

Question 4

how does adrenaline affect heart behavior?
> molecularly

Answer 4

targets adrenergic B-receptors on myocytes

these receptors coupled to G-stim proteins so a signalling cascade occurs where increase in L-type calcium channels on membrane

Increase open probability and amplitude of current

Question 5

what is isoprenaline?

Answer 5

synthetic analogue of adrenaline
> stable
> long half life

use to investigate how adrenaline affects calcium current

Question 6

how can whole cell current be changed?
> mathmatical model

Answer 6

increase no. of functional channels
increase channel open probability
alter the single cell current

these will all affect the whole cell current

Question 7

what is barium used for in electrophysiological experiements?

Answer 7

substitute for calcium as a charge carrier as it produces a bigger current making it easier to record

current are longer too as there iss no calcium-induced inhibition

Question 8

why must calcium electrophysio measure I/V relationship from -40mV instead of resting membrane potential of -70mV?

Answer 8

To avoid activating the sodium channels and recording the sodium currents

so use a higher voltage to isolate the L-type calcium channels

Question 9

how does open state of a ion channel change?

Answer 9

different modes of opening
> 0 closed
> 1 rapid 1ms opening
> 2 prolonged 20ms opening

Question 10

how does adrenaline influence whole cell current (Ca-Ltype)?

Answer 10

can increase the amplitude of current
can increase open state probability of L-type channel

so whole cell current increases

Question 11

how does PKA become activated?

Answer 11

cAMP second messenger able to activate PKA and release its catalytic subunits to phosphorylate targets

Question 12

how does PKA activate L-type calcium channels?

Answer 12

by phosphorylating the channel at a specific consensus sequences

there are many PKA phosph sites along structure of the channel

Question 13

how does PKA target L-type calcium channels specifically ?

Answer 13

there is AKAP which helps to colocalise PKA to the L-type calcium channel instead of it’s other cell targets

Question 14

how was the L-type channel activation pathway discovered?

Answer 14

electrophysiological expreirments using pharmacological agents to ACTIVATE or INHIBIT different parts of signalling pathway slowly enabled reconstitution of pathway

Question 15

what are some key features of the L-type calcium channel
> structure

Answer 15

similar to potassium but with added
> EF hand calcium sensor
> AKAP binding site
> phosphorylation PKA sites
> proximal and distal CTD for autoinhibition

Question 16

how is the CTD of L-type calcium channel related to its function?

Answer 16

CTD responsible for autoinhibitory effects
> removal of CTD leads to higher current amplitude

Question 17

can autoinhibition of L-type calcium current be overcome?

Answer 17

Yes, phosphorylation of specific residues on CTD is able to relieve autoinihibtion

RAD GTPase phosphorylation also relieves inhibition

Question 18

how does phosphorylation affect calcium and potassium channel activity?

Answer 18

increase Ca activity creating powerful contraction

inhibit K channel, reducing excitability

Question 19

how can phosphorylation status of cells be maintained?

Answer 19

needs to be ATP activity and kinase/phosphatase to regulate the process

Question 20

how does AKAP interact with calcium channel?

Answer 20

there is leucine zipper motif that AKAP recognises

mutations in motif associated with LQTS

Question 21

how does SNS and PNS influnce channel behavior? How does this affect the contractile heart?

Answer 21

adrenaline increase Ica and inhibit Ik = increase force of contraction

Ach enhance Ik and reduce Ica = reduced contraction

Question 22

how do the PNS and SNS pathways interact to control ion channel behavior?
> behavior of Ica-L

Answer 22

these pathways can influence each other
> chronic adrenergic (SNS) can lead to off (PNS) pathway as seen in chronic heart failure

Question 23

what is pathology of chronic heart failure?

Answer 23

inadequate CO and to compensate SNS/contraction increases

but compensation unable to resolve problem and blunted response to adrenaline = furthur reduction of CO [positive feedback]