Effects of Single Nucleotide Polymorphisms (SNPs) on BK K+ Channel Properties

Large-conductance, calcium-activated potassium (BK) channels are widely expressed and acquire functional heterogeneity through alternative splicing, auxiliary subunits (β1-4, γ1-4), and posttranslational modifications. An additional mechanism with the potential to alter channel properties is natural genetic variation via single nucleotide polymorphisms (SNPs). Five SNPs in the gene encoding the pore-forming α subunit of BK, Kcnma1, were predicted to have potentially deleterious effects on channel properties. To determine whether these SNPs could alter BK currents, we introduced the SNPs into two human BK variants expressed in HEK293T cells, encoding muscle and brain-type channels (hBKQEERL and hBKVYR, respectively). We found that an autism-linked SNP (A138V), located in the ‘core’ channel intracellular S0-S1 linker, had little effect on current properties, while two non-disease-linked SNPs (C495G and R800W) in the C-terminal gating ring affected the conductance-voltage relationship and kinetics across multiple Ca2+ conditions in the context of both BK variants. Although the conductance-voltage relationships of the hBKQEERL and hBKVYR variants differed across Ca2+ conditions, R800W consistently produced rightward shifts in the V1/2 values, while C495G produced leftward shifts in the V1/2 values. These results suggest that SNP effects are additive in combination with splice variant effects in channel properties and implicate naturally occurring human genetic variation as a potential modulator of BK channel function.