Rod and cone photoreceptors in the vertebrate retina provide the organism with two alternative and complementary signaling systems that support the full behavioral range of the visual system. In general, the photoresponse in rods is slower in time course, more sensitive to light and adapts over a more restricted range of intensities than that of cones. Within a given species, cones sensitive to different wavelengths of light may also differ in their photosensitivity and kinetics. The long term objective in this research is to understand the mechanisms of phototransduction in retinal photoreceptors, and to explain the difference in transduction between the two receptor types. Ca ions in the cytoplasm of the outer segment in cone photoreceptors play a critical role in phototransduction. Yet, the Ca concentration in darkness and the magnitude and time course of changes expected to follow illumination are unknown. Also, the mechanisms that regulate Ca concentration and the mechanisms through which Ca achieves its function in transduction are generally not known from direct investigation, rather, they are inferred by analogy to the processes discovered in rod photoreceptors.
The specific aims of this proposal are to investigate the concentration, function and homeostasis of Ca in cone outer segments. Recent discoveries suggest that rods and cones differ in the rate and extent of voltage- and light-dependent changes in Ca concentration in their outer segments, in the Ca permeability of their cGMP-dependent ion channels as well as in the attributes of Ca-dependent biochemical processes in the outer segment. Using an indicator dye, we propose to measure the Ca concentration in the outer segment of isolated cone photoreceptors and to determine the magnitude and time course of light-dependent changes in this concentration. We will investigate the role of Ca in cone outer segments as modulator of three different biochemical processes: the activity of the enzyme guanylate cyclase, the photoactivation of the enzyme phosphodiesterase and the binding of cGMP to cGMP-gated ion channels. We will conduct these studies both in intact cones and in truncated outer segments using electrophysiological and photometric techniques. Using electrophysiological methods we will study the Ca permeability of the cGMP-gated channels of cones as well as their macroscopic and microscopic kinetics. We will also investigate the structural determinants of ion flow through these channels by combining electrophysiological methods with techniques of molecular biology.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY005498-11
Application #
2159445
Study Section
Visual Sciences C Study Section (VISC)
Project Start
1984-07-01
Project End
1999-06-30
Budget Start
1995-07-01
Budget End
1996-06-30
Support Year
11
Fiscal Year
1995
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Physiology
Type
Schools of Medicine
DUNS #
073133571
City
San Francisco
State
CA
Country
United States
Zip Code
94143
Korenbrot, Juan I; Mehta, Milap; Tserentsoodol, Nomingerel et al. (2013) EML1 (CNG-modulin) controls light sensitivity in darkness and under continuous illumination in zebrafish retinal cone photoreceptors. J Neurosci 33:17763-76
Korenbrot, Juan I (2012) Speed, sensitivity, and stability of the light response in rod and cone photoreceptors: facts and models. Prog Retin Eye Res 31:442-66
Rebrik, Tatiana I; Botchkina, Inna; Arshavsky, Vadim Y et al. (2012) CNG-modulin: a novel Ca-dependent modulator of ligand sensitivity in cone photoreceptor cGMP-gated ion channels. J Neurosci 32:3142-53
Korenbrot, Juan I (2012) Speed, adaptation, and stability of the response to light in cone photoreceptors: the functional role of Ca-dependent modulation of ligand sensitivity in cGMP-gated ion channels. J Gen Physiol 139:31-56
Miller, J L; Korenbrot, J I (1993) In retinal cones, membrane depolarization in darkness activates the cGMP-dependent conductance. A model of Ca homeostasis and the regulation of guanylate cyclase. J Gen Physiol 101:933-60
Picones, A; Korenbrot, J I (1992) Permeation and interaction of monovalent cations with the cGMP-gated channel of cone photoreceptors. J Gen Physiol 100:647-73
Maricq, A V; Korenbrot, J I (1990) Inward rectification in the inner segment of single retinal cone photoreceptors. J Neurophysiol 64:1917-28
Maricq, A V; Korenbrot, J I (1990) Potassium currents in the inner segment of single retinal cone photoreceptors. J Neurophysiol 64:1929-40
Maricq, A V; Korenbrot, J I (1988) Calcium and calcium-dependent chloride currents generate action potentials in solitary cone photoreceptors. Neuron 1:503-15
Hestrin, S; Korenbrot, J I (1987) Effects of cyclic GMP on the kinetics of the photocurrent in rods and in detached rod outer segments. J Gen Physiol 90:527-51

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