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PHOTOSENSORY TRANSDUCTION IN CILIATES. II. POSSIBLE ROLE OF G‐PROTEIN AND cGMP IN Stentor coeruleus
Author(s) -
Fabczak Hanna,
Park PhunBum,
Fabczak Stanislaw,
Song PillSoon
Publication year - 1993
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.1751-1097.1993.tb02941.x
Subject(s) - phosphodiesterase , cyclic guanosine monophosphate , transducin , guanosine , biology , g protein , protein subunit , pertussis toxin , biochemistry , activator (genetics) , cyclic nucleotide , cyclic adenosine monophosphate , microbiology and biotechnology , signal transduction , endocrinology , receptor , nucleotide , enzyme , nitric oxide , gene
Abstract— The heterotrichous ciliate, Stentor coerulus , exhibits a welll defines photophobic response to a sudden increase in the intensity of visible light. the phobic reactions usually appear with a latency perios (i.e. a time delay between the onset of the stimulus and the stop response). This latency of phobic response was significatly increased when the cells werw incubated with 8‐bromo‐guanosine3′,5′‐cyclic monophospjhate. In the presence of this nucleotide, a reduction of cell responsiveness (i.e. the number of photophobically responding cells) was also observed. similar effects were observed when cells were treated with pertussis toxin, a G‐protein activity modulator, and 3′‐isobutyl‐methylxanthine, an inhibitor of guanosine 3′, 5′‐cyclic monophosphate (cGMP) phosphodiesterase. the G‐protein activator fluoroaluminate and 6‐anilino‐5,8‐quinolinedione (LY 83583) (an effective agent for lowerin cellular cGMP levels) showed opposite effects on hte cell photophobic response. These result indirectly suggesnt that the level of cytoplamic cGMP, possibly modulated by a G‐protein‐coupled CGMP phosphodiesterase, plays a phototreasducing role in Stentor . In addition, using an antiserum raised against bovine transducin, a cross reacting protein with an apparent molecular mass of 39 kDa was detected on immunoblots. The α‐subunits of a Stentor G‐protein has also been partially cloned and sequenced. However, the possible coupling between the G‐protein and the putative phosphodiesterase remains to be established.