Photosensory transduction in ciliates. Role of intracellular pH and comparison between Stentor coeruleus and Blepharisma japonicum.
To test the hypothesis that light signal transduction in the unicellular ciliates Stentor coeruleus and Blepharisma japonicum involves a change in intracellular pH as an initial signal following photoexcitation, we studied the dependence of the photophobic responses of the cells to changes in extracellular pH and to reagents that specifically affect intracellular pH. The extracellular pH can modify not only the intracellular pH, but can even reverse the sign of the pH gradient across the cell membrane. Thus, as predicted by the hypothesis, low extracellular pH reversibly inhibited the photophobic response of the ciliates. The intracellular pH-modulating reagents tested included ammonium chloride, a membrane-permeable weak acid that lowers the intracellular pH, and the protonophores carbonylcyanide m-chlorophenyl-hydrazone (CCCP) and carbonylcyanide p-(trifluoromethoxy)-phenyl-hydrazone (FCCP), which collapse the pH gradient across the cell membrane. The low pH and protonophore treatments caused a gradual inhibition of the photophobic responses in both ciliates. The observed reduction of the responsiveness of the cells to visible light can be attributed to the alteration of the intracellular pH, which is suggested to play a specific role in the photosensory transduction in both Stentor coeruleus and Blepharisma japonicum.
Fabczak
H
H
Department of Cell Biology, Polish Academy of Science, Warsaw.
Fabczak
S
S
Song
P S
PS
Checcucci
G
G
Ghetti
F
F
Lenci
F
F
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002465:Cell Movement / Q000187:drug effects / Q000528:radiation effects; D016798:Ciliophora / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D008027:Light; D015398:Signal Transduction; D013045:Species Specificity
D000643:Ammonium Chloride; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone