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FUNCTIONAL ROLE OF CALCIUM IN PHOTORECEPTOR CELLS
Author(s) -
Miki Naomasa,
Kuo CheHui,
Hayashi Yokichi,
Akiyama Mariko
Publication year - 1980
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1980.tb03795.x
Subject(s) - membrane , chemistry , biophysics , calcium , biochemistry , biology , organic chemistry
— Ca‐uptake by disc membranes prepared from frog rod photoreceptor outer segments was examined. Ca‐uptake study revealed two affinity sites which were saturated with 10– 5 M and 10– 3 M of ATP. When disc membranes in 20 m M Tris‐HCl buffer (pH 7.5) were stored at ‐20°C for 6 h, more than 95% of Ca‐uptake activity was lost. Ca‐uptake activity was, however, preserved if the disc membrane suspension was mixed with 1–10m M ATP and stored at ‐20°C. Furthermore the reactivation of Ca‐uptake was observed if disc membranes, which had lost Ca‐uptake ability by storing at 4°C for 3 h, were mixed with 10 m M ATP and then frozen at ‐20°C for 5 h or 28 h (ATP‐induced ATP‐dependent Ca‐uptake). When the contents of ATP bound to disc membranes were measured during a brief aging at 37°C, the decrement of bound ATP content was correlated well with the decreasing of Ca‐uptake activity. Carbonylcyanide m ‐chlorophenylhydrazone (CCCP), a conductor of protons, inhibited Ca‐uptake activity and half maximal inhibition was achieved at 2 × 10– 8 M. When 10– 6 M of CCCP was added to the 45 Ca‐accumulated disc membranes, rapid release of 45 Ca from the disc membranes was observed. These results suggest that ATP may play a role in the Ca‐pump regulation in disc membranes and a [H + ] gradient across disc membrane may be linked to Ca‐uptake mechanism.