Guanylate cyclase activity in retinal homogenates of transgenic mice at 0 µM [Ca²⁺] and 2 µM [Ca²⁺].

<p>Guanylate cyclase activity (pmol cGMP/min.mg prot) was determined in WT, GCAPs−/−, GCAPs−/− bGCAP2 line E and GCAPs−/− bEF⁻GCAP2 line A retinal extracts at 0 µM [Ca²⁺] or 2 µM [Ca²⁺] conditions, in the absence or presence of 3 µM recombinant GCAP2. In WT retinal homogenates at 0 µM [Ca²⁺] the endogenous GCAPs activate RetGC activity about 8-fold over the activity at 2 µM [Ca²⁺]. This stimulation of RetGC activity at 0 µM [Ca²⁺] is lost in GCAPs−/− retinal homogenates, but restored in the GCAPs−/− bGCAP2 line E, which indicates that the control bGCAP2 protein expressed <i>in vivo</i> as a transgene is active in these assays. However, retinal homogenates from GCAPs−/−bEF⁻GCAP2 line A mice showed greatly reduced RetGC activity at 0 µM [Ca²⁺] and no activity at 2 µM [Ca²⁺] conditions. Addition of 3 µM recombinant GCAP2 elicited activation of RetGC at 0 µM [Ca²⁺] in all retinal homogenates, indicating the presence of functional RetGC in all samples. These results show that bEF⁻GCAP2 was present, but mostly inactive, in GCAPs−/−bEF⁻GCAP2 line A retinal homogenates. Results show the mean and standard deviation of at least four independent experiments.