|
|
|
|
|
|
|
||
The Journal of General Physiology, Vol 98, 95-130, Copyright © 1991 by The Rockefeller University Press
ARTICLES |
T Tamura, K Nakatani and KW Yau
Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Membrane current was recorded from a single primate rod with a suction pipette while the cell was bath perfused with solutions maintained at a temperature of approximately 38 degrees C. A transient inward current was observed at the onset of bright illumination after briefly exposing the outer segment in darkness to Ringer's (Locke) solution containing 3- isobutyl-1-methylxanthine (IBMX), an inhibitor of cGMP phosphodiesterase. After briefly removing external Na+ from around the outer segment in darkness, a similar current was observed upon Na+ restoration in bright light. By analogy to amphibian rods, this inward current was interpreted to represent the activity of an electrogenic Na(+)-dependent Ca2+ efflux, which under physiological conditions in the light is expected to reduce the free Ca2+ in the outer segment and provide negative feedback (the "Ca2+ feedback") to the phototransduction process. The exchange current had a saturated amplitude of up to approximately 5 pA and a decline time course that appeared to have more than one exponential component. In the absence of the Ca2+ feedback, made possible by removing the Ca2+ influx and efflux at the outer segment using a 0 Na(+)-0 Ca2+ external solution, the response of a rod to a dim flash was two to three times larger and had a longer time to peak than in physiological solution. These changes can be approximately accounted for by a simple model describing the Ca2+ feedback in primate rods. The dark hydrolytic rate for cGMP was estimated to be 1.2 s-1. The incremental hydrolytic rate, beta*(t), activated by one photoisomerization was approximately 0.09 s-1 at its peak, with a time-integrated activity, integral of beta*(t)dt, of approximately 0.033, both numbers being derived assuming spatial homogeneity in the outer segment. Finally, we have found that primate rods adapt to light in much the same way as amphibian and other mammalian rods, such as showing a Weber-Fechner relation between flash sensitivity and background light. The Ca2+ feedback model we have constructed can also explain this feature reasonably well.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  J. Fan, M. L Woodruff, M. C Cilluffo, R. K Crouch, and G. L Fain Opsin activation of transduction in the rods of dark-reared Rpe65 knockout mice J. Physiol., October 1, 2005; 568(1): 83 - 95. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S Nymark, H Heikkinen, C Haldin, K Donner, and A Koskelainen Light responses and light adaptation in rat retinal rods at different temperatures J. Physiol., September 15, 2005; 567(3): 923 - 938. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. L. Makino, R.L. Dodd, J. Chen, M.E. Burns, A. Roca, M.I. Simon, and D.A. Baylor Recoverin Regulates Light-dependent Phosphodiesterase Activity in Retinal Rods J. Gen. Physiol., June 1, 2004; 123(6): 729 - 741. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. L. Fain, H. R. Matthews, M. C. Cornwall, and Y. Koutalos Adaptation in Vertebrate Photoreceptors Physiol Rev, January 1, 2001; 81(1): 117 - 151. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. M. Schneeweis and J. L. Schnapf The Photovoltage of Macaque Cone Photoreceptors: Adaptation, Noise, and Kinetics J. Neurosci., February 15, 1999; 19(4): 1203 - 1216. [Abstract] [Full Text] [PDF]
|
|
|
|
