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Calcium release from rod outer segments: Evidence for a cGMP-sensitive calcium binding protein
Ist Teil von
Biochemical and biophysical research communications, 1991-04, Vol.176 (1), p.70-78
Ort / Verlag
San Diego, CA: Elsevier Inc
Erscheinungsjahr
1991
Quelle
Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)
Beschreibungen/Notizen
Numerous studies investigating the cGMP-gated cation conductance in rod disk membranes have purported to measure efflux of Ca
2+ entrapped in rod disk membrane vesicles. We have utilized sonication and osmotic shock as additional tests for sensitivity of cGMP- and A23187-induced Ca
2+ release to elimination of the transvesicular Ca
2+ gradient. We find that
1) Treatment with sonication or osmotic shock in low Ca
2+ medium does not release Ca
2+ from either native
cGMP
Ca
2+
-loaded
vesicles or solubilized, reconstituted “Ca
2+-loaded” vesicles,
2) 70–100% of the cGMP-induced “flux” and 90–100% of the A23187-induced Ca
2+ “flux” is insensitive to elimination of the Ca
2+ gradient by sonication or osmotic shock in low Ca
2+ medium, and
3) total amount of releasable Ca
2+ is related to membrane surface area rather than vesicle entrapment volume. We conclude that
1) A23187 disrupts binding of Ca
2+ to proteins and phospholipids as well as releasing entrapped Ca
2+ and
2) a large fraction of the cGMP-induced release observed in rod disk vesicles is due to release of bound Ca
2+.