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I. Ocular Physiology > Phototransduction (F) > Flashcards

Phototransduction (F) Flashcards

1
Q

Where is the biochemical cascade of phototransduction restricted to?

A

outer segment of photoreceptors

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2
Q

Where is protein production and oxidative metabolism is restricted to?

A

inner segment of photoreceptors

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3
Q

Where are the outer and inner segments of the photoreceptor connected?

A

cilium

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4
Q

What is the microtubule arrangement of the cilium?

A

9+0

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5
Q

What is the resting membrane potential of rods in the dark?

A

-40mV

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6
Q

Where is the localized Na+-K+-ATPase in the photoreceptor?

A

inner segment membrane

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7
Q

Where does the potassium channel allows the flow of K+ ions back out of the photoreceptor cell along its concentration gradient?

A

inner segment membrane

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8
Q

What is the cGMP-gated channel also called? 1. What passes through the channel? 2. Where is it located? 3

A
  1. CNG channel (cyclic nucleotide-gated)
  2. Non-discriminate: Na+, K+, Ca2+ (mostly Na+) into cell
  3. outer segment membrane of photorecptor
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9
Q

What is the cGMP-gated channel also called? 1. What passes through the channel? 2. Where is it located? 3

A
  1. CNG channel (cyclic nucleotide-gated)
  2. Non-discriminate: Na+, K+, Ca2+ (mostly Na+) into cell
  3. outer segment membrane of photorecptor
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10
Q

Where is the NCKX channel located? 1. What does it exchange? 2

A
  1. outer segment membrane

2. 1 molecule of K+ and Ca2+ leave cell while 4 Na+ enter the cell

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11
Q

Why is there a low basal level of calcium in dark-adapted rods?

A

there is an inward leak of Ca2+ (via CNG) preventing an extremely low intracellular [Ca2+]

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12
Q

What are the regulators of cGMP (and what do each of them do)?

A
  1. guanylate cyclase (GC) (Synthesizes cGMP)

2. cGMP phosphodiesterase (PDE6) (degrades cGMP to GMP)

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13
Q

What are the regulators of cGMP (and what do each of them do)? 1-2. Are these more active in the light or the dark? 3

A
  1. guanylate cyclase (GC) (Synthesizes cGMP)
  2. cGMP phosphodiesterase (PDE6) (degrades cGMP to GMP)
  3. light
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14
Q

What is a transmembrane G protein coupled receptor (GPCR) photon receptor for the dark? 1. When is it inactive?

A
  1. Rhodopsin

2. dark

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15
Q

What does Rhodopsin do when activated?

A

catalyzes the activation of a heterotrimeric G-protein (Transducin)

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16
Q

What does guanylyl cyclase and phosphodiesterase do?

A

turns GTP to cGMP

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17
Q

What does guanylyl cyclase and phosphodiesterase do?

A

turns GTP to cGMP

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18
Q

What is the inverse agonist that rhodopsin is bound to while inactive?

A

11-cis retinal

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19
Q

When in dark-state what neurotransmitter is consistently in the vesicles?

A

glutamate

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20
Q

When a photon is absorbed by rhodopsin what happens to 11-cis retinal?

A

all become trans retinal

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21
Q

What does trans retinal do to rhodopsin?

A

converts it to Metarhodopsin II (R*)

22
Q

Does Metarhodopsin II have a higher or lower affinity than rhodopsin?

A

higher

23
Q

Does Metarhodopsin II have a higher or lower affinity than rhodopsin?

A

higher

24
Q

What decreases GDP affinity for Metarhodopsin II and dissociates from it?

A

Gtα-GTP

25
Q

What does Gtα-GTP have an increased affinity for? 1. WHat does this do? 2

A
  1. PDE6

2. converts cGMP to GMP

26
Q

What does a small reduction in cGMP do to channels?

A

large effect on channel closure

27
Q

What does channel closure in due to the reduction in cGMP lead to?

A
  1. reduces the flow of Na+ ions into the cell
  2. reduces the dark current and makes the membrane potential more negative and hyperpolarized
  3. flux of Ca2+ into the cell is also reduced and NCKX
28
Q

What are the mechanisms to block Metarhodopsin II?

A
  1. Phosphorylation by Rhodopsin kinase (RK1)
  2. Arrestin binding to MII
  3. Schiff’s base hydrolysis
  4. cGMP restoration
29
Q

What increases with lowering of cytoplasmic [Ca2+] in recovery?

A

Guanylate cyclase

30
Q

Even after MII quenching PDE6 will remain active until what happens?

A

GTP unbinds from G-protein which makes PDE6 inactivated

31
Q

Even after MII quenching PDE6 will remain active until what happens?

A

GTP unbinds from G-protein which makes PDE6 inactivated

32
Q

What is a GTPase accelerating (activating) protein and will cause hydrolysis of the GTP to GDP associated with activated transducin?

A

RGS9-1

33
Q

What is a GTPase accelerating (activating) protein and will cause hydrolysis of the GTP to GDP associated with activated transducin?

A

RGS9-1

34
Q

What can occur if enough photons (bright light) are absorbed such that all channels are closed?

A

saturation

35
Q

The sensitivity of the phototransduction system leads to a high potential for what?

A

“noise amplification”

36
Q

What are the types of opsin in cones?

A

S-Cones: S-opsin
M-Cones: M-opsin
L-Cone: L-opsin

37
Q

Are rods or cones more sensitive?

A

rods

38
Q

Are spontaneous isomerization rates of cone opsins less than or greater than Rhodopsin? 1. Do rods or cones have lower spatial and temporal resolution? 2

A
  1. greater

2. rods

39
Q

Do rods or cones have a greater convergence of photoreceptors to a single retinal ganglion cell?

A

rods

40
Q

Do rods or cones have faster phototransduction cascade kinetics? 1. What does this mean for saturation? 2

A
  1. cones

2. cones saturate less

41
Q

Where on the retina are there only cones?

A

fovea

42
Q

How many rod bipolar cell types are there? 1. Cone cell types? 2.

A
  1. 1

2. 10

43
Q

What are the two types of bipolar cells?

A
  1. On-center or depolarizing bipolar cells (DBC)

2. Off-center or hyperpolarizing bipolar cells (HBC)

44
Q

What are the two types of bipolar cells?

A
  1. On-center or depolarizing bipolar cells (DBC)

2. Off-center or hyperpolarizing bipolar cells (HBC)

45
Q

What is the major difference of HBC cells and DBC cells?

A

When stimulated HBC cation channels close and the cell becomes hyperpolarized. When stimulated DBC cation channels open, and the cell becomes depolarized

46
Q

What is the major difference of HBC cells and DBC cells?

A

When stimulated HBC cation channels close and the cell becomes hyperpolarized. When stimulated DBC cation channels open, and the cell becomes depolarized

47
Q

What are the glutamate receptors in HBC cells? 1. In DBC cells? 2

A
  1. AMPA and KA

2. mGlur6 glutamate receptor

48
Q

When bipolar cells (HBC or DBC) are depolarized where do they release glutamate to?

A

ganglion cells

49
Q

Do hyperpolarizing bipolar cells increase or decrease their release of glutamate to its synapsed ganglion cell? 1. Does this decrease or increases its firing rate? 2

A
  1. decrease

2. decrease

50
Q

Do depolarizing bipolar cells increase or decrease their release of glutamate to its synapsed ganglion cell? 1. Does this decrease or increases its firing rate? 2

A
  1. increase

2. increase

I. Ocular Physiology (20 decks)

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