HCN1 and retinitis pigmentosa 1: The absence of HCN1 in CNGB1-knockout (K/O) mice resulted in an increased deterioration of photoreceptor cells, underscoring the notion that suppressing HCN channels could exacerbate the progression of RP [Schön et al., 2016; but see Della Santina et al., 2010 for no effect on the speed of retinal degeneration when comparing the retinas of normal mice and those treated with ivabradine, in the rd10 and wild-type (wt) mice].