Stimulates two retinal guanylyl cyclases (GCs) GUCY2D and GUCY2F when free calcium ions concentration is low, and inhibits GUCY2D and GUCY2F when free calcium ions concentration is elevated (By similarity). This Ca(2+)-sensitive regulation of GCs is a key event in recovery of the dark state of rod photoreceptors following light exposure (By similarity). May be involved in cone photoreceptor response and recovery of response in bright light (By similarity). . This is the function of GUCA1B (guanylate cyclase activator 1B, Ensembl gene identifier ENSG00000112599).