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Bleached pigment activates transduction in salamander cones
M C Cornwall1, H R Matthews, R K Crouch
1Department of Physiology, Boston University School of Medicine, Massachusetts 02118, USA.
The Journal of General Physiology
|September 1, 1995
Summary
Pigment bleaching in salamander cones accelerates guanylyl cyclase velocity, mimicking background light. This effect, potentially an "equivalent background" excitation, can be reversed by 11-cis retinal or beta-ionone.
Area of Science:
- Phototransduction in vertebrate vision
- Cellular physiology of photoreceptors
Background:
- Understanding the mechanisms of light adaptation in retinal cones is crucial for visual processing.
- Previous studies in rods suggested light-activated pigment affects the transduction cascade.
Purpose of the Study:
- To investigate the impact of pigment bleaching on guanylyl cyclase velocity in isolated salamander cones.
- To compare the effects of background light and pigment bleaching on cone phototransduction.
Main Methods:
- Suction electrode recording in isolated salamander (Ambystoma tigrinum) cones.
- Rapid solution steps into 0.5 mM IBMX to measure guanylyl cyclase velocity.
- Experimental manipulation using background light, pigment bleaching, and retinal analogue treatments.
Main Results:
- Both background light and pigment bleaching accelerate guanylyl cyclase velocity in cones.
- Cyclase velocity increases with percent pigment bleached and saturates with background intensity.
- The bleaching effect on cyclase rate persists for 15-20 minutes and is reversible with 11-cis retinal or beta-ionone.
Conclusions:
- Cone pigment bleaching induces an "equivalent background" excitation of the transduction cascade.
- Bleached and light-activated pigments have distinct effects on cone phototransduction.
- The mechanism may be similar to that observed in retinal rods.