Purchase this article with an account.
G. L. Fain, M. L. Woodruff, T. Wang, F. A. Concepcion, J. C. Chen; Background Light Modulates PDE Rate in Mouse Rods. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1117.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
We have previously shown that steady light decreases tauD of the flash response in mouse rods, suggesting that backgrounds modulate the rate of PDE turnoff. To assess the contribution of PDE modulation to light adaptation, we have examined the effect of backgrounds on rods lacking GCAPs (to eliminate cyclase regulation) and/or lacking the CNG channel calmodulin binding site (to eliminate channel modulation).
We used a stable line of transgenic mice lacking both GCAPs (Mendez et al 2001 PNAS 98:9948). In a second line of mice called CNGB1deltaCaM, a targeted mutation was introduced into the endogenous CNGB1 gene locus to remove amino acids 227-241; this deletes the calmodulin-binding site. Suction-electrode recordings from single rods were made with standard techniques.
Recordings from GCAPs-/- rods confirmed previous results: much of adaptation survives deletion of cyclase regulation. Responses to light steps showed a prominent sag, flash response turnoff was accelerated in the presence of background light as in WT rods, and sensitivity in background light was many orders of magnitude greater than expected from response compression. Rods from CNGB1deltaCaM mice behaved much like WT rods; we could find no significant differences in sensitivity, circulating current, or integration time, though tauD was somewhat reduced. Weber’s Law behavior of CNGB1deltaCaM rods was identical to WT. Rods from mice that were both GCAPs-/- and CNGB1deltaCaM responded much like GCAPs-/- rods: responses to light steps again show a prominent sag, flash response turnoff in the presence of background light was accelerated, and sensitivity in background light was much greater than expected from response compression and identical to that of GCAPs-/- rods. Of particular interest, the CNGB1deltaCaM/GCAPs-/- rods showed prominent (15-20 pA) undershoots when steady light was extinguished. These undershoots cannot be caused by cyclase modulation, channel modulation, or modulation of Rh* lifetime (which could not increase [cGMP] above its normal dark-adapted level at light off) but can only be produced by modulation of PDE.
Our experiments show that considerable light adaptation persists even after removal of both cyclase and channel modulation and confirm previous indications that regulation of the rate of the PDE plays an important role in adaptation to steady background light.
This PDF is available to Subscribers Only