Lens Water and Ion Transport (F)

Question 1

Where does water enter the lens?

Answer 1

the anterior and posterior poles

Question 2

Where does water leave the lens?

Answer 2

equatorial region

Question 3

What drives water circulation in the lens?

Answer 3

ion transporters “pumps”

Question 4

What drives water circulation in the lens?

Answer 4

ion transporters “pumps”

Question 5

Which surface of the cells face the aqueous?

Answer 5

basal surface

Question 6

How are the tight junctions arranged in the lens?

Answer 6

Wide spacing can be observed between lens epithelial cells and “leaky”

Question 7

How are the tight junctions arranged in the lens?

Answer 7

Wide spacing can be observed between lens epithelial cells and “leaky”

Question 8

What is the benefit of having extracellular space between the lens fibers?

Answer 8

allows for fluid flow and access to lateral surfaces for fluid absorption and ion transport

Question 9

What connexin proteins are found in the lens epithelium?

Answer 9

Cx43 and Cx50

Question 10

What connexin proteins are found in the lens fibers?

Answer 10

Cx46 and Cx50

Question 11

What connexin stimulates lens epithelial cell proliferation in the germinative zone?

Answer 11

Cx50

Question 12

Are gap junctions found between lens epithelial cells and lens fibers at the anterior pole? 1. Are gap junctions found between lens fiber cells and between lens fiber cells and lens epithelial cells at the equatorial region? 2

Answer 12

1. no

2. yes

Question 13

What aquaporin is a lens-specific aquaporin found only in lens fiber cells and has a significantly decreased ability to allow water to pass through?

Answer 13

Aquaporin 0

Question 14

Is the concentration of Na+ low or high in the lens cells?

Answer 14

low

Question 15

Where is the Na+/K+ ATPase found in high levels in the lens? 1. How does it impact the lens circulation? 2

Answer 15

1. lens fibers at the equatorial region

2. circulation is dependent on pump function

Question 16

Where is the Na+/K+ ATPase found in high levels in the lens? 1. How does it impact the lens circulation? 2

Answer 16

1. lens fibers at the equatorial region

2. circulation is dependent on pump function

Question 17

What maintains the cell volume?

Answer 17

concentrations of Cl- (higher in extracellular space)

Question 18

Which part of the lens has a greater difference in charge?

Answer 18

greater peripherally than centrally

Question 19

Do central lens cells have a Cl- influx or efflux (why)? 1. What about the peripheral lens (why)? 2

Answer 19

1. influx (concentration gradient outcompetes electrochemical gradient)
2. efflux (electrochemical gradient outcompetes concentration gradient)

Question 20

In what location would blocking Cl- channels cause cell swelling? 1. In what location would it cause extracellular swelling? 2

Answer 20

1. peripheral fiber cells

2. central fiber cells

Question 21

What are the ion transport proteins involved in Cl- movement?

Answer 21

NKCC1, KCC1, KCC4, KCC3, KCC4

Question 22

What are the ion transport proteins involved in Cl- movement?

Answer 22

NKCC1, KCC1, KCC4, KCC3, KCC4

Question 23

What drives glucose into the lens cells? 1. What is the transporter? 2

Answer 23

1. Na+ gradient

2. SGLT2

Question 24

What are utilized to generate the tripeptide glutathione (cysteine, glycine, glutamate)?

Answer 24

amino acid transporters

Question 25

What are the two major regulators of Calcium homeostasis?

Answer 25

1. intracellular to extracellular transport of Calcium

2. Storage within the ER

Question 26

What are the intracellular to extracellular transporters of Calcium (and what are their actions)?

Answer 26

1. Na+/Ca2+ exchanger (NCX) (Uses sodium gradient to pump out calcium)
2. plasma membrane Ca2+ -ATPase (PMCA) (uses ATP to pump out Ca2+)

Question 27

What is storage of calcium within the ER mediated by?

Answer 27

SERCA