Page 364 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

D. Activation of photosensors and adaptation
Rhodopsin 1 MR-II (metarhodopsin II)
Disk membrane
β
Transducin β γ MR II γ
–70 mV
–40 mV α s α s
I PDE I PDE Sensor
PDE GDP GTP PDE potential
Light
Inactive GDP 2 active
Darkness
cGMP 4 Light stimulus 5‘-GMP cGMP
Na + 5
ICF of rod Channel
cGMP decreases ICF 2+ closes Visual Acuity, Photosensors II
3 Ca 2+ Channel Ca
opens Channel closes
GCAP
active
Na + Influx of 2+ Na +
2+
2+
[Ca ] i = Ca /Na + [Ca ] decreases 2+
350-500 nmol/L [Ca ] i
6
P De- Hyper- 7 P Plate 12.21
polarization polarization CaM
CaM
Plasma membrane Phos- β γ β γ Phos- Plasma membrane
P
ECF ducin-P Glutamate release ducin ECF
Low
High
Dark-adapted
Signal: “Light“ Light-adapted
E. Regeneration cycles
1 Retinal cycle 2 Rhodopsin cycle
Recoverin
All-trans-retinal Arrestin P Ca 2+ Light
P
P RK
All-trans-retinol (rhodopsin
Pigmented epithelium Rhodopsin MR II Transducin
kinase)
11-cis-retinol β γ
Opsin
11-cis-retinal α s
3 Transducin cycle Dark- β γ
Transducin adapted
β Phos- α s
β γ γ Light- ducin GDP I PDE
adapted
α s
GDP
β I PDE P i
MR II γ PDE GAP α s
GTP I PDE
α s 351
GDP GDP
Despopoulos, Color Atlas of Physiology © 2003 Thieme
All rights reserved. Usage subject to terms and conditions of license.