Lecture 10 - Smooth Muscle

Question 1

Describe the nuclear location and quantity in smooth muscle.

Answer 1

One nucleus per cell that is centrally located.

Question 2

Smooth muscle cells do not have ___-____; they have small invaginations called _______ instead.

Answer 2

T-Tubules

Caveolae

Question 3

Smooth muscle can be composed such that it acts as a single unit, where cells are connected via ____ ______, or as multiple, individual units when not connected. The latter allows for finer control (e.g. iris of the eye).

Answer 3

Gap junctions

Question 4

The ratio of actin:myosin in smooth muscle is much _______ than in skeletal or cardiac muscle. Also, smooth muscle lacks ______ (one of the proteins in skeletal and cardiac muscle thin filaments). Smooth muscle has characteristic dense bodies where the intermediate filaments ____ and ____ anchor actin (analogue of z-discs.)

Answer 4

Greater

Troponin

Desmin

Vimentin

Question 5

Describe the smooth muscle contraction process.

Answer 5

Increase in intracellular Ca++ –> Ca++ binds Calmodulin –> Ca++/Calmodulin complex activates myosin light chain kinase to make it more active(keep in mind MLCK activity is constiutively high in skeletal and cardiac muscle)–> phosphorylates light chains in myosin heads to increase ATPase activity.

Question 6

In response to ß2 adrenergic agonists, smooth muscle cells increase ______ –> activates PKA –> phosphorylates (which deactivates) _______ –> decreased myosin ATPase activity –> smooth muscle relaxation. This processes is dependent on the G__ subunit of the ß2 adrenergic receptor (a GPCR).

Keep in mind smooth muscle can also relax in response to _____ released from endothelial cells –> this pathway leads to the activation of PKG –> increases intracellular ______ –> which eventually leads to increased activity of MYLCK-P –> dephosphorylates MLC –> decreased MLC activity.

Answer 6

cAMP

MLCK

Gs

NO

cGMP

Question 7

Smooth muscle cell contraction cycling undergoes a “______” state, in which the myosin heads remain in the powerstroke position longer than compared to moysin heads in skeletal or cardiac muscle. Only _____% of myosin heads need to remain phosphorylated in smooth muscle cells for this state to be maintained.

Answer 7

“Latch” state

30%

Question 8

Smooth muscle can contract in both a phasic and tonic manner. Which one is mostly associated with hormonal, pharmacological, and metabolic factors, and which one is mostly associated with neural stimulation?

Answer 8

Tonic is mostly associated with hormonal, pharmacological, and metabolic factors, while Phasic is mostly associated with neruonal stimulation.