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Calcium release from rod outer segments: evidence for a cGMP-sensitive calcium binding protein
1Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06510.
Biochemical and Biophysical Research Communications
|April 15, 1991
Summary
Calcium (Ca2+) release from rod disk vesicles, often attributed to cGMP-gated channels, is largely due to bound Ca2+ rather than transvesicular flux. This challenges previous interpretations of Ca2+ efflux studies in retinal rod cells.
Area of Science:
- Biochemistry
- Cell Biology
- Vision Science
Background:
- Rod disk membranes are crucial for phototransduction in the eye.
- Previous studies suggested cGMP-gated channels mediate Ca2+ efflux from these vesicles.
Purpose of the Study:
- To re-evaluate the mechanisms of Ca2+ release from rod disk membrane vesicles.
- To determine if Ca2+ release is truly transvesicular or due to bound Ca2+.
Main Methods:
- Utilized sonication and osmotic shock to eliminate Ca2+ gradients.
- Investigated Ca2+ release induced by cyclic guanosine monophosphate (cGMP) and A23187.
- Compared Ca2+ release from native and reconstituted vesicles.
Main Results:
- Sonication/osmotic shock did not release Ca2+ from loaded vesicles.
- Most cGMP- and A23187-induced Ca2+ release was insensitive to gradient elimination.
- Releasable Ca2+ correlated with membrane surface area, not vesicle volume.
Conclusions:
- A23187 affects bound Ca2+ and releases entrapped Ca2+.
- A significant portion of cGMP-induced Ca2+ release originates from bound Ca2+ in rod disk vesicles.