Lens Metabolism (F)

Question 1

What transports glucose into cells from the ciliary process stroma using sodium concentration gradient? 1. What cells are these found? 2

Answer 1

1. SGLT/Sodium Glucose cotransporter

2. pigmented ciliary epithelial cells

Question 2

Through what does glucose exit non-pigmented ciliary epithelial cells through facilitated diffusion?

Answer 2

GLUT

Question 3

Which GLUT is primarily of the lens epithelium? 1. Which glut is primarily in lens fibers and decreases towards the center of the lens? 2. Which has a higher affinity? 3

Answer 3

1. GLUT1
2. GLUT3
3. GLUT3

Question 4

What are the main sources of lenitcular oxygen?

Answer 4

1. diffusion across the cornea (major)

2. retinal vasculature (minor)

Question 5

Does the anterior lens or posterior lens have more oxygen?

Answer 5

anterior

Question 6

When oxygen is high what happens to HIF-1? 1. When it is low what happens to HIF-1? 2

Answer 6

1. covalently modifed (ubiquitinated) and is targeted for proteolysis
2. enter the nucleus and facilitate the transcription and expression of specific genes important for lens growth

Question 7

When oxygen is high what happens to HIF-1? 1. When it is low what happens to HIF-1? 2

Answer 7

1. covalently modifed (ubiquitinated) and is targeted for proteolysis
2. enter the nucleus and facilitate the transcription and expression of specific genes important for lens growth

Question 8

What is the relationship between HIF-1 and p27?

Answer 8

HIF-1 increases the expression of p27, which decreases lens cell proliferation

Question 9

As lens fibers go from superficial fiber to the central nuclear fibers, what is the relative number of mitochondria present?

Answer 9

decreases superficial to central

Question 10

What is the majority of lens ATP is derived from?

Answer 10

glycolysis

Question 11

Is lens fiber cell metabolism mostly aerobic or anaerobic?

Answer 11

anaerobic

Question 12

Because glycolysis predominates, what accumulates in the cells?

Answer 12

lactate and lactic acid

Question 13

Is the pH lower or higher in the central nucleus?

Answer 13

lower

Question 14

What does low pH do to gap junctions?

Answer 14

decreases permeability

Question 15

What make up gap junctions which are still permeable at low pH?

Answer 15

specific connexon proteins

Question 16

What make up gap junctions which are still permeable at low pH?

Answer 16

specific connexon proteins

Question 17

What contributes to the oxidants found in the lens?

Answer 17

1. some ATP is generated via oxidative phosphorylation (aerobic metabolism) generating free radicals
2. UV light absorbed by lens fiber proteins/DNA
3. H2O2 is also produced by lens mitochondria via superoxide dismutase

Question 18

What contributes to the oxidants found in the lens?

Answer 18

1. some ATP is generated via oxidative phosphorylation (aerobic metabolism) generating free radicals
2. UV light absorbed by lens fiber proteins/DNA
3. H2O2 is also produced by lens mitochondria via superoxide dismutase

Question 19

What is a tripeptide made of glutamine, cysteine, and glycine, found at a very high concentration in the lens that prevents oxidation of lens proteins by becoming oxidized itself?

Answer 19

Glutathione

Question 20

Where is Glutathione produced? 1. How is it transported into the lens epithelial cells? 2

Answer 20

1. lens epithelial cells, superficial lens fibers

2. sodium dependent transport protein

Question 21

What are the forms of glutathione found in the lens cells?

Answer 21

reduced (GSH), or oxidized (GSSG)

Question 22

How does oxidized ascorbate enter the lens? 1. How is it reduced? 2

Answer 22

1. glucose transporters

2. glutathione

Question 23

What are the mechanisms to protect against H2O2?

Answer 23

1. Lens epithelial cells have abundant catalase

2. Glutathione peroxidase