Characterization of Ca2+-binding protein 5 knockout mouse retina
Fred Rieke 1,
Amy Lee 2,
and
Francoise Haeseleer 3*
1 Physiology and Biophysics, University of Washington, Seattle, Washington, United States
2 Dept of Pharmacology and Center for Neurodegenerative Disease, Emory University, Atlanta, Georgia, United States
3 Department of Ophthalmology, University of Washington, 1959, NE Pacific St--Box 356485, Seattle, Washington, 98195-6485, United States
* To whom correspondence should be addressed. E-mail: fanfan{at}u.washington.edu.
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Abstract |
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Purpose: The goal of this study was to investigate whether Ca2+-binding protein 5 (CaBP5) is required for vision using CaBP5 knockout mice. We also tested whether CaBP5 can modulate expressed Cav1.2 voltage-activated calcium channels.
Methods: CaBP5 knockout (Cabp5-/-) mice were generated. The retinal morphology and visual function of six-week-old Cabp5-/- mice was analyzed by confocal and electron microscopy, by single flash electroretinography (ERGs) and whole-cell patch-clamp recordings of retinal ganglion cells. The interaction and modulation of Cav1.2 channels by CaBP5 was analyzed using affinity chromatography, gel overlay assays and patch-clamp recordings of transfected HEK293 cells.
Results: No evidence of morphological changes and no significant difference in the amplitude of the ERG responses were observed in CaBP5 knockout mice compared with wild-type mice. However, the sensitivity of retinal ganglion cell light responses was reduced by ~50% in Cabp5-/- mice. CaBP5 directly interacted with the CaM-binding domain of Cav1.2 and colocalized with Cav1.2 in rod bipolar cells. In transfected HEK293T cells, CaBP5 suppressed calcium-dependent inactivation of Cav1.2 and shifted the voltage-dependence of activation to more depolarized membrane potentials.
Conclusion: This study provides evidence that lack of CaBP5 results in reduced sensitivity of rod-mediated light responses of retinal ganglion cells, suggestive of a role for CaBP5 in the normal transmission of light signals throughout the retinal circuitry. The interaction, colocalization and modulation of Cav1.2 by CaBP5 suggest that CaBP5 can alter retinal sensitivity through modulation of voltage-gated calcium channels.
Key Words:
knockout animals, bipolar cell, Ca2+ channels, ganglion cell, Ca2+ binding protein
