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Flashcards in Adrenoceptors and the heart Deck (44):
1

Heart SNS receptors

B1, some a1 on contractility

2

Heart PNS

Mostly M2

3

Blood vessels SNS

Predominantly a1 for contraction, some B2 for relaxation.

4

Bronchi SNS

Non-innervated B2 relax

5

Bronchi PNS

M3 contract and increase secretion

6

GI tract SNS

Decrease motility (all except a2), sphincters contract and glandular cells decrease secretion (a2)

7

GI tract PNS

All M receptors; increase motility, sphincters relax, glands secrete.

8

Kidney SNS

B1; increase renin secretion

9

Liver SNS

glucose release; a1 mediated.

10

Eye SNS

radial muscle; a1 contracts.
Ciliary muscle; B2 relaxes
Lacrimal glands; a increases secretion.

11

M3 in eye

Cause contraction of sphincter muscle, ciliary muscle and increased secretion.

12

SNS in ejaculation

a1

13

PNS in erection

M3 and NO

14

Urinary sphincters

Contract; a1
relax; NO

15

Detrusor muscle

Relax; B3,
Contract; M3

16

a1 intracellular cascade

Gq/11 --> PLC. Increased Ca++ and PKC activation via IP3 and DAG

17

a2 intracellular cascade

Gi/o; By directly inhibits VGCC. a decreases phosphorylation which inhibits VGCC

18

B receptor intracellular cascade

Gs; leads to cAMP (If current) and PKA rise (increase in VGCC activation and inactivation of MLCK)

19

Adrenaline on CVS

Increases heart rate, decreases TPR, increases BP slightly

20

Noradrenaline on CVS

Increase in TPR increases BP significantly, so baroreceptor reflex decreases heart rate.

21

Isoprenaline on CVS

Decrease in peripheral resistance, increase in heart rate, decrease in BP due to diastolic decrease.

22

B3 receptor in heart

Negative inotropic effect; possibly 'safety valve' for high [catecholamine].

23

Mimicking B1 stimulation in heart.

Use cholera toxin or forskolin.

24

Effect of B1 stimulation of heart.

increases cAMP so PKA so increases Ca++ entry;
1) Inotropic effect
2) Sensitises ryanodine receptors
3) PKA phosphorylates SERCA and phospholamban.
4) Chronotropic effect
5) Enhances effect of delayed rectifier K+ channels.

25

Effects of M2 stimulation on heart.

Negative chronotropic effect to due to decreased cAMP and PKA but not inotropic as confined to nodal tissue.
If activation shifted to more negative levels.
Ik-ACh hyperpolarises cell.

26

Na+ channels structure

a subunit forms pore; B to do with trafficking. Relatively TTX insensitive in the heart.

27

Channels with S4 charged TM domain on each subunit

NaV, CaV and Kv channels. voltage sensor

28

Inactivation loop between domain 3 and 4 and linker chain on 4.

NaV

29

CaV structure

a1 = pore. a2d and B = channel trafficking

30

L-type CaVs

Phosphorylation enhances sensitivity
Sensitive to Ca++ blockers.

31

T-type channels

only occur in nodal and conductive tissue, not in contractile tissue.

32

Kv channel mutations

Lead to episodic ataxia and long QT syndrome (latter also by NaV mutations).

33

Kv channels distribution

None in nodal tissue

34

Kv channel inactivation

N-type; N-terminal occludes.
C-type; movement of residues near extracellular surface.

35

Shaker K channels

Kv channels

36

Kir channels; role

maintenance of resting potential without loss of K+ during d'poln. Unknown in liver and kidney. Carry I(k1).

37

Kir channels; structure

2 transmembrane domains

38

Why do Kir channels close?

Due to Mg++ and polyamine (e.g. spermine) occlusion.

39

Kir subfamilies

Inward rectifiers, ACh responsive, ATP-sensitive.

40

HGIRK channels

Kir channels; activated by By subunit on M2 stimulation; leads to hyperpolarisation.

41

ATP sensitive K+ channels; sulphonylureas

Sulphonylurea drugs close to stimulate insulin secretion

42

ATP sensitive K+ channels; smooth muscle

Opening causes relaxation; anti-hypertensive drug target.

43

ATP sensitive K+ channels; ATP

Closes. Also protects from ischaemia.

44

HCN channels structure

6TM structure with S4 = voltage sensor, S5-S6 selectivity pore. Present in heart and brain.