Abstract
During illumination. Ca2+ enters fly photoreceptor cells through light-activated channels that are located in the rhabdomere, the compartment specialized for phototransduction. From the rhabdomere. Ca2+ diffuses into the cell body. We visualize this process by rapidly imaging the fluorescence in a cross section of a photoreceptor cell injected with a fluorescent Ca2+ indicator in vivo. The free Ca2+ concentration in the rhabdomere shows a very fast and large transient shortly after light onset. The free Ca2+ concentration in the cell body rises more slowly and displays a much smaller transient. After approximate to 400 ms of light stimulation, the Ca2+ concentration in both compartments reaches a steady state, indicating that thereafter an amount of Ca2+. equivalent to the amount of Ca2+ flowing into the cell, is extruded. Quantitative analysis demonstrates that during the steady state, the free Ca2+ concentration in the rhabdomere and throughout the cell body is the same. This shows that Ca2+ extrusion takes place very close to the location of Ca2+ influx, the rhabdomere. because otherwise gradients in the steady-state distribution of Ca2+ should be measured. The close colocalization of Ca2+ influx and Ca2+ extrusion ensures that, after turning off the light, Ca2+ removal from the rhabdomere is faster than from the cell body. This is functionally significant because it ensures rapid dark adaptation.
Original language | English |
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Pages (from-to) | 8578-8583 |
Number of pages | 6 |
Journal | Proceedings of the National Academy of Sciences of the United States of America |
Volume | 97 |
Issue number | 15 |
DOIs | |
Publication status | Published - 18-Jul-2000 |
Keywords
- LIMULUS VENTRAL PHOTORECEPTORS
- LIGHT-SENSITIVE CHANNELS
- HAIR-CELLS
- DROSOPHILA PHOTORECEPTORS
- BLOWFLY PHOTORECEPTORS
- CA2+ CHANNEL
- IN-VIVO
- TRP
- LOCALIZATION
- EXCHANGE