The second non-visual arrestin cloned was first termed β-arrestin-2 (retroactively changing the name of β-arrestin into β-arrestin-1), even though by that time it was clear that non-visual arrestins interact with hundreds of different GPCRs, not just with β2-adrenergic receptor. Systematic names, arrestin-2 and arrestin-3, respectively, were proposed soon after that. Arrestin-4 was cloned by two groups and termed cone arrestin, after photoreceptor type that expresses it, and X-arrestin, after the chromosome where its gene resides.