| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Biophysical Journal 12: 1073-1094 (1972)
© 1972 the Biophysical Society
ABSTRACT
The shapes of the photocurrent responses of rat rods, recorded with microelectrodes from the receptor layer of small pieces of isolated retinas, have been investigated as a function of temperature and of stimulus energy. Between 27 and 37°C the responses to short flashes can be described formally as the output of a chain of at least four linear low-pass filters with time constants in the range 50-100 msec. The output of the filter chain is then distorted by a nonlinear amplitude-limiting process with a hyperbolic saturation characteristic. Flashes producing 
30 photons absorbed per rod yield responses of half-maximal size independently of temperature. The maximum response amplitude is that just sufficient to cancel the dark current. The rate of rise of a response is proportional to flash energy up to the level of 105 photons absorbed per rod, where hyperbolic rate saturation ensues. The responses continue to increase in duration with even more intense flashes until, at the level of 107 photons absorbed per rod, they last longer than 50 min. The time-courses of the photocurrent and of the excitatory disturbance in the rod system are very similar. The stimulus intensity at which amplitude saturation of the photocurrent responses begins is near that where psychophysical "rod saturation" is seen. An analysis of these properties leads to the following conclusions about the mechanism of rod excitation. (a) The kinetics of the photocurrent bear no simple relation to the formation or decay of any of the spectroscopic intermediates so far detected during the photolysis of rhodopsin. (b) The forms of both the amplitude- and rate-limiting processes are not compatible with organization of rhodopsin into "photoreceptive units" containing more than 300 chromophores. Even at high stimulus intensities most rhodopsin chromophores remain connected to the excitatory apparatus of rods. (c) The maximum rate of rise of the photocurrent is too fast to be consistent with the infolded disks of a rod outer segment being attached to the overlying plasma membrane. Most of the disks behave electrically as if isolated within the cell. (d) Control of the photocurrent at the outer segment membrane is not achieved by segregation of the charge carriers of the current within the rod disks. Instead, it is likely to depend on control of the plasma membrane permeability by an agent released from the disks.
This article has been cited by other articles:
 |
|
 |
|
  B. G. Borghuis, C. P. Ratliff, R. G. Smith, P. Sterling, and V. Balasubramanian Design of a Neuronal Array J. Neurosci., March 19, 2008; 28(12): 3178 - 3189. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Knopp and H. Ruppel Calcium-Sensitive Downregulation of the Transduction Chain in Rod Photoreceptors of the Rat Retina Biophys. J., August 1, 2006; 91(3): 1078 - 1089. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. W. Xu, M. Hou, and M. M. Slaughter Photoreceptor encoding of supersaturating light stimuli in salamander retina J. Physiol., December 1, 2005; 569(2): 575 - 585. [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]
|
|
|
|
 |
|
 T. I. Rebrik and J. I. Korenbrot In Intact Mammalian Photoreceptors, Ca2+-dependent Modulation of cGMP-gated Ion Channels Is Detectable in Cones but Not in Rods J. Gen. Physiol., December 29, 2003; 123(1): 63 - 76. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T Tamura, K Nakatani, and K. Yau Light adaptation in cat retinal rods Science, August 18, 1989; 245(4919): 755 - 758. [Abstract] [PDF]
|
|
|
|
|
|
C. Stromeyer 3rd, R. Kronauer, and J. Madsen Apparent saturation of blue-sensitive cones occurs at a color-opponent stage Science, October 13, 1978; 202(4364): 217 - 219. [Abstract] [PDF]
|
|
|
|
|
|
E. Adelson Iconic storage: the role of rods Science, August 11, 1978; 201(4355): 544 - 546. [Abstract] [PDF]
|
|
|
|
|
|
B Sakitt Locus of short-term visual storage Science, December 26, 1975; 190(4221): 1318 - 1319. [Abstract] [PDF]
|
|
|
|
|
|
G. Fain Quantum sensitivity of rods in the toad retina Science, March 7, 1975; 187(4179): 838 - 841. [Abstract] [PDF]
|
|
|
|
|
|
S. Yoshikami, W. E. Robinson, and W. A. Hagins Topology of the Outer Segment Membranes of Retinal Rods and Cones Revealed by a Fluorescent Probe Science, September 27, 1974; 185(4157): 1176 - 1179. [Abstract] [PDF]
|
|
|
|
|
|
G. L. Fain and J. E. Dowling Intracellular Recordings from Single Rods and Cones in the Mudpuppy Retina Science, June 15, 1973; 180(4091): 1178 - 1181. [Abstract] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
