metabotropic receptors

Question 1

pathways of GPCR include

indirect channel modulation

Answer 1

cAMP (a SU)- Gs/ Gi

PLC (a SU) - Gq - IP3

Question 2

direct channel modulation

Answer 2

via G protein itself
not via enzymes/ 2nd

• beta/gamma SU binds directly to GIRK K channel; on cardiac myocytes
• triggers hyper polarisation of cells
• decreased excitability
• mAChRs
• reduced HR - PNS

Question 3

pre SN R

Post SN R

Answer 3

effect NT release at synapse

effect neuronal excitability and AP firing - mAChR (GIRK)

Question 4

post-ganglionic SNS neurone (pre- SN)

Answer 4

• synapses with smooth muscle target in periphery
• NAd release
• pre SN a2 R + VGCa
• modulation of Ca current via beta/gamma SU
• activation of a2 inhibits VGC via beta/gamma signalling directly
• reduced ca conductance/influx
• reduced Nad release from terminals

Question 5

regulation of pre- synaptic transmission can be via

Answer 5

inhibition of NT release (reduced ca influx)

facilitation of NT release (VGKC) - inhibit delayed rectifier channel

• prolonged AP
• enhanced ca influx due to more pos Vm because of reduced K conductance
• longer EPSP

Question 6

receptors can be activated by

Answer 6

same
or different neurones in that chain

• CNS
• Nad release from neighbouring synapses can reduce the release of glutamate from glutaminergic neurones - a2 R

Question 7

post SN modulation on..

Answer 7

autonomic ganglia

• ACh always
• post G neuron
• modulates AP firing in that cell

Question 8

Fast EPSP

Answer 8

• ACh binds to nAChR
• single AP
• na influx
• large depol
  (synapse not stimulated)- current stimulus only

Question 9

slow EPSP

Answer 9

• ACh binds to mACHr
• IP3 pathway (a SU) - Gq protein
• DAG produced (2nd messenger)
• inhibits M-type K channels
• less k efflux, reduced resting conductance to k (open without stimulation)
• small depol due to leak Na channels
• no AP fired initially

Question 10

ACh release leads to

Answer 10

fast and slow EPSPs

Question 11

No slow EPSP

Answer 11

• M-type open
• k efflux
• reduced excitability
  . single AP only
• difficult to reach vT

Question 12

slow EPSP

Answer 12

• M-T channels close (mACHr)
• increased excitability of cell
• now if stimulated by current
• multiple Eps fire
• repeated stimulation of same synapse enhances response

Question 13

mACHr activation in ANS…

Answer 13

increases neuronal excitability