Desensitization of the photoresponse in Limulus ventral photoreceptors by protein kinase C precedes rhabdomere disorganization and endocytosis

Limulus photoreceptors utilize the phosphoinositide pathway to generate light-induced single photon events (quantum bumps) that sum to form the depolarizing receptor potential. The protein kinase C (PKC) activator, (−)-indolactam V (ILV) rapidly desensitizes the light response in Limulus ventral ner...

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Bibliographic Details
Published in:Visual neuroscience 2003-05, Vol.20 (3), p.241-248
Main Authors: DABDOUB, ALAIN, JINKS, ROBERT N., WANG, YOUJUN, BATTELLE, BARBARA-ANNE, PAYNE, RICHARD
Format: Article
Language:English
Subjects:
Animals
Biochemistry. Physiology. Immunology
Biological and medical sciences
Crustacea
Endocytosis - physiology
Enzyme Activation - physiology
Fluorescent Antibody Technique
Fundamental and applied biological sciences. Psychology
Horseshoe Crabs - physiology
Indoles - pharmacology
Inhibition
Invertebrates
Lactams - pharmacology
Light
Microscopy, Electron
Microvilli
Microvilli - ultrastructure
Photoreceptor Cells - drug effects
Photoreceptor Cells - radiation effects
Photoreceptor Cells - ultrastructure
Physiology. Development
PKC
Protein Kinase C - metabolism
Protein Kinase C - physiology
Quantum bumps
Retina - cytology
Retina - physiology
Retina - ultrastructure
Time Factors
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Summary:Limulus photoreceptors utilize the phosphoinositide pathway to generate light-induced single photon events (quantum bumps) that sum to form the depolarizing receptor potential. The protein kinase C (PKC) activator, (−)-indolactam V (ILV) rapidly desensitizes the light response in Limulus ventral nerve photoreceptors. Within 10 min of extracellular application, 100 nM (−)-ILV caused a decrease in the mean amplitude of quantum bumps to 38% of control values. PKC activation by (−)-ILV also causes photosensitive membrane disorganization and endocytosis. To investigate whether this precedes desensitization of the electrical response, we fixed cells after 10-min incubation with 25 μM (−)-ILV, a concentration sufficient to cause a 1000-fold desensitization of the receptor potential. The photosensitive microvilli of these photoreceptors remained narrow, densely packed, and well organized. Increasing the incubation time to 60 min did, however, induce disorganization and swelling of the microvilli and endocytosis of the photosensitive membrane, as previously reported. Measurement of membrane capacitance did not indicate a significant reduction in membrane area accompanying desensitization by (−)-ILV. PKC-induced reduction in light sensitivity therefore precedes the detection of ultrastructural changes in the rhabdomeral membrane and is not due to a net loss of membrane.
ISSN:0952-5238
1469-8714
DOI:10.1017/S0952523803203035