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THE ROLE OF CALCIUM IN Chlamydomonas PHOTOMOVEMENT RESPONSES AS ANALYSED BY CALCIUM CHANNEL INHIBITORS
Author(s) -
Hegemann P.,
Neumeier K.,
Hegemann U.,
Kuehnle E.
Publication year - 1990
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.1751-1097.1990.tb01802.x
Subject(s) - phototaxis , chlamydomonas , calcium channel , calcium , biology , verapamil , biophysics , dihydropyridine , voltage dependent calcium channel , diltiazem , microbiology and biotechnology , biochemistry , chemistry , botany , organic chemistry , mutant , gene
— Phototaxis and light‐induced stop responses in Chlamydomonas are known to be calcium dependent. We show that phototaxis is stereoselectively inhibited by dihyropyridines, verapamil, diltiazem, ω‐conotoxin and pimozide, all inhibitors of slow L‐type calcium channels. In contrast, the stop response in Chlamydomonas can be specifically reduced only by ω‐conotoxin and pimozide. The light‐regulated calcium uptake as detected by 45 calcium can be completely suppressed by verapamil and ω‐conotoxin but not by diltiazem or any of the dihyropyridine‐type calcium channel inhibitors. We conclude that phototaxis and stop response in Chlamydomonas are regulated by three distinguishable drug receptor sites. One of them controls phototaxis and is sensitive to verapamil. The second site controls stop response and phototaxis and shows a high sensitivity to ω‐conotoxin and pimozide. These two drug receptors seem to be localized in the plasma membrane and function as ion channels. In addition, calcium influences internal signal transduction from the photoreceptor to the flagella. This internal role of calcium is inhibited by the dihydropyridine binding to a dihydropyridine receptor protein. The arylazide‐l,4‐dihydropyridine[ 3 H]azidopine binds with a K d = 35 n M to a 50 kDa protein located in one of the internal cell membranes. Azidopine binding is fully reversible and can be partially inhibited by nimodipine and PN‐200110. This protein is the first identified dihyropyridine receptor in an unicellular plant cell. It might serve as an internal calcium regulating channel in Chlamydomonas.