The Journal of General Physiology
CrossRef
  Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents
This Article
Right arrow Full Text
Right arrow Full Text (PDF, 804K)
Right arrow PPT slides of all figures
Right arrow Alert me when this article is cited
Right arrow Citation Map
Services
Right arrow Email this article
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new content in the JGP
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Nikonov, S.
Right arrow Articles by Pugh, E.N.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Nikonov, S.
Right arrow Articles by Pugh, E.N., Jr.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Facebook   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?
© The Rockefeller University Press, 0022-1295/1998//7/ $5.00
Journal of General Physiology, Volume 111, Number 1, 1998

Article

Kinetics of Recovery of the Dark-adapted Salamander Rod Photoresponse

S. Nikonov*,||, N. Engheta{ddagger},§, and E.N. Pugh, Jr.*,§

From the * Department of Psychology, {ddagger} Department of Electrical Engineering, and § Institute of Neurological Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104; and || Institute of Cellular Biophysics, Puschino, Russia 142292

The kinetics of the dark-adapted salamander rod photocurrent response to flashes producing from 10 to 105 photoisomerizations ({Phi}) were investigated in normal Ringer's solution, and in a choline solution that clamps calcium near its resting level. For saturating intensities ranging from ~102 to 104 {Phi}, the recovery phases of the responses in choline were nearly invariant in form. Responses in Ringer's were similarly invariant for saturating intensities from ~103 to 104 {Phi}. In both solutions, recoveries to flashes in these intensity ranges translated on the time axis a constant amount ({tau}c) per e-fold increment in flash intensity, and exhibited exponentially decaying "tail phases" with time constant {tau}c. The difference in recovery half-times for responses in choline and Ringer's to the same saturating flash was 5–7 s. Above ~104 {Phi}, recoveries in both solutions were systematically slower, and translation invariance broke down. Theoretical analysis of the translation-invariant responses established that {tau}c must represent the time constant of inactivation of the disc-associated cascade intermediate (R*, G*, or PDE*) having the longest lifetime, and that the cGMP hydrolysis and cGMP-channel activation reactions are such as to conserve this time constant. Theoretical analysis also demonstrated that the 5–7-s shift in recovery half-times between responses in Ringer's and in choline is largely (4–6 s) accounted for by the calcium-dependent activation of guanylyl cyclase, with the residual (1–2 s) likely caused by an effect of calcium on an intermediate with a nondominant time constant. Analytical expressions for the dim-flash response in calcium clamp and Ringer's are derived, and it is shown that the difference in the responses under the two conditions can be accounted for quantitatively by cyclase activation. Application of these expressions yields an estimate of the calcium buffering capacity of the rod at rest of ~20, much lower than previous estimates.

Key Words: G-protein cascade • signal transduction • photoreceptors • calcium • guanylyl cyclase

Address correspondence to E.N. Pugh, Jr., Department of Psychology, University of Pennsylvania, 3815 Walnut Street, Philadelphia, PA 19104-6196. Fax: 215-573-3892; E-mail: pugh{at}psych.upenn.edu


Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Facebook Facebook   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?


This article has been cited by other articles:


Home page
 JGPHome page
D. Tranchina
The Calculus of Rod Phototransduction
J. Gen. Physiol., January 1, 1998; 111(1): 3 - 6.
[Full Text] [PDF]


  Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents