Extremely rapid recovery of human cone circulating current at the extinction of bleaching exposures.
We used a conductive fibre electrode placed in the lower conjunctival sac to record the a-wave of the human photopic electroretinogram elicited by bright white flashes, delivered during, or at different times after, exposure of the eye to bright white illumination that bleached a large fraction (approximately 90%) of the cone photopigment. During steady-state exposures of this intensity, the amplitude of the bright-flash response declined to approximately 50% of its dark-adapted level. After the intense background was turned off, the amplitude of the bright-flash response recovered substantially, for flashes presented within 20 ms of background extinction, and fully, for flashes presented 100 ms after extinction. In addition, a prominent 'background-off a-wave' was observed, beginning within 5-10 ms of background extinction. We interpret these results to show, firstly, that human cones are able to preserve around half of their circulating current during steady-state illumination that bleaches 90% of their pigment and, secondly, that following extinction of such illumination, the cone circulating current is restored within a few tens of milliseconds. This behaviour is in stark contrast to that in human rods, where the circulating current is obliterated by a background that bleaches only a few percent of the pigment, and where full recovery following a large bleach takes at least 20 min, some 50,000 times more slowly than shown here for human cones.
Kenkre
J S
JS
Division of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 0200, Australia.
Moran
N A
NA
Lamb
T D
TD
Mahroo
O A R
OA
D000200:Action Potentials / Q000502:physiology; D000221:Adaptation, Ocular / Q000502:physiology*; D003623:Dark Adaptation / Q000502:physiology*; D004596:Electroretinography; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012168:Retinal Pigments / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology
D012168:Retinal Pigments