0 -> Galpha_GTP 0 -> Galpha_GTP Galpha_GTP -> 0 Galpha_GTP -> 0 0 -> APLC APLC -> 0 0 -> IP3 IP3 -> 0 (1/1000)*Ca_ER -> (1/100)*Ca_Cyt (1/100)*Ca_Cyt -> (1/1000)*Ca_ER (1/20)*Ca_Cyt -> 0 0 -> (1/20)*Ca_Cyt