Smooth Muscle Contraction and Relaxation

Question 1

Does smooth muscle have troponin?

Answer 1

No

Question 2

Describe the arrangement of actin and myosin in smooth muscle

Answer 2

Random - not striated

Question 3

What are the 2 types of smooth muscle?

Answer 3

Single unit

Multiunit

Question 4

What are the characteristics of single unit smooth muscle?

Answer 4

Not all cells innervated
Depolarisation spreads through gap junctions
Has pacemaker cells
Common

Question 5

What are the characteristics of multiunit smooth muscle?

Answer 5

Each cell innervated
No gap junctions
Less common

Question 6

What is the role of Ca2+ in smooth muscle contraction?

Answer 6

Ca-CaM activates myosin light chain kinase (MLCK)
MLCK phosphorylates myosin light chain - forms cross-bridges with actin - contraction
MLC-phosphatase dephosphorylates myosin
Overall activity depends on balance between MLCK and phosphatase
Ca2+ inhibits MLCP indirectly - prevents dephosphorylation

Question 7

Which GPCR types cause smooth muscle contraction?

Answer 7

Gq-linked - e.g. Alpha1-adrenoceptors, M3 receptors

Question 8

What is the effect of G12/13 activation on muscle contraction?

Answer 8

Activates Rho-GEF - activates RhoA - activates RhoK - inhibits MLCP

Question 9

Name 2 alpha1 adrenoceptor agonist treatments acting on smooth muscle contraction

Answer 9

Adrenaline - treats anaphylactic shock - raise blood pressure
Phenylephrine - treats nasal congestion - constricts blood vessels

Question 10

Name 2 mAChR agonist treatments acting on smooth muscle contraction

Answer 10

Pilocarpine - treats glaucoma - pupil constriction - increases intraocular fluid drainage
Bethanechol - treats urinary retention

Question 11

Which enzyme is required for nitric oxide synthesis?

Answer 11

Nitric oxide synthase (NOS)

Question 12

Which endothelial cell receptor types stimulate NO release, causing vasodilation, and what are their ligands?

Answer 12

M3 receptors - ACh
H1 - histamine
BK2 - bradykinin