The SLC24 Family of K+-Dependent Na+–Ca2 + Exchangers: Structure–Function Relationships

Abstract The human SLC24 gene family contains five members encoding the NCKX1–5 proteins that function as K + -dependent Na + –Ca 2 + exchangers. NCKX proteins have been shown to play critical roles in retinal rod and cone photoreceptors, olfactory neurons, epidermal melanocytes, and the retinal pigment epithelium. NCKX transcripts are also found in many other tissues, in particular throughout the brain, but their specific physiological roles yet need to be elucidated in most cases. Here, we focus on our current knowledge of NCKX transport function as has been described in detail only for in situ NCKX1 in the outer segments of retinal rod photoreceptors and on structure–function relationships elucidated for the NCKX2 isoform after expression of its (mutated) cDNA in cell lines.