ae , ▁an ▁extension ▁of ▁the ▁end op las mic ▁ret icul um , ▁and ▁cause ▁release ▁of ▁calci um , ▁but ▁this ▁process ▁does ▁not ▁seem ▁to ▁be ▁essential ▁for ▁normal ▁vision . ▁ ▁Cal ci um ▁bind s ▁to ▁prote ins ▁such ▁as ▁cal mod ul in ▁( Ca M ) ▁and ▁an ▁eye - specific ▁protein ▁kin ase ▁C ▁( PK C ) ▁known ▁as ▁In a C . ▁These ▁prote ins ▁interact ▁with ▁other ▁prote ins ▁and ▁have ▁been ▁shown ▁to ▁be ▁necessary ▁for ▁shut ▁off ▁of ▁the ▁light ▁response . ▁In ▁addition , ▁prote ins ▁called ▁arrest ins ▁bind ▁met ar hod ops in ▁and ▁prevent ▁it ▁from ▁activ ating ▁more ▁G q . ▁A ▁sod ium - cal ci um ▁ex ch anger ▁known ▁as ▁Cal X ▁p umps ▁the ▁calci um ▁out ▁of ▁the ▁cell . ▁It ▁uses ▁the ▁in ward ▁sod ium ▁gradient ▁to ▁export ▁calci um ▁at ▁a ▁sto ichi ometry ▁of ▁ 3 ▁Na + / ▁ 1 ▁Ca ++ . ▁ ▁TR P , ▁In a C , ▁and ▁P LC ▁form ▁a ▁signal ing ▁complex ▁by ▁binding ▁a ▁sc aff old ing ▁protein ▁called ▁In a D . ▁In a D ▁contains ▁five ▁binding ▁domains ▁called ▁P D Z ▁domain ▁prote ins , ▁which ▁specifically ▁bind ▁the ▁C ▁term ini ▁of ▁target ▁prote ins . ▁Dis ruption ▁of ▁the ▁complex ▁by ▁mut ations ▁in ▁either ▁the ▁P D Z ▁domains ▁or ▁the ▁target ▁prote ins ▁reduces ▁the ▁efficiency ▁of ▁signal ing