▁in ▁D ros oph ila ). ▁When ▁rh od ops in ▁( R h ) ▁absor bs ▁a ▁phot on ▁of ▁light ▁its ▁chrom oph ore , ▁ 1 1 - cis - 3 - h ydro xy ret inal , ▁is ▁is omer ized ▁to ▁all - trans - 3 - h ydro xy ret inal . ▁Rh ▁under go es ▁a ▁conform ational ▁change ▁into ▁its ▁active ▁form , ▁met ar hod ops in . ▁Met ar hod ops in ▁activ ates ▁G q , ▁which ▁in ▁turn ▁activ ates ▁a ▁ph osph ol ip ase ▁C β ▁( PL C β ) ▁known ▁as ▁Nor p A . ▁ ▁P LC β ▁hydro ly zes ▁ph osph at id y lin os it ol ▁( 4 , 5 )- bis ph osph ate ▁( PI P 2 ), ▁a ▁ph osph ol ip id ▁found ▁in ▁the ▁cell ▁memb rane , ▁into ▁sol ub le ▁in os it ol ▁tri ph osph ate ▁( IP 3 ) ▁and ▁dia cy l gly cer ol ▁( DA G ), ▁which ▁stays ▁in ▁the ▁cell ▁memb rane . ▁D AG ▁or ▁a ▁derivative ▁of ▁D AG ▁causes ▁a ▁calci um - select ive ▁ion ▁channel ▁known ▁as ▁trans ient ▁re ceptor ▁potential ▁( TR P ) ▁to ▁open ▁and ▁calci um ▁and ▁sod ium ▁flows ▁into ▁the ▁cell . ▁IP 3 ▁is ▁thought ▁to ▁bind ▁to ▁IP 3 ▁re cept ors ▁in ▁the ▁sub r hab dom er ic ▁c is tern