Abstract

BK K+ channels are critical regulators of neuron and muscle excitability, comprised of a tetramer of pore-forming asubunits from the KCNMA1 gene and cell-and tissue-selective 13 subunits (KCNMB1-4). Mutations in KCNMA1 are associated with neurological disorders, including autism. However, little is known about the role of neuronal BK channel 13 subunits in human neuropathology. The 132 subunit is expressed in central neurons and imparts inactivation to BK channels, as well as altering activation and deactivation gating. In this study, we report the functional effect of G124R, a novel KCNMB2 mutation obtained from whole-exome sequencing of a patient diagnosed with autism spectrum disorder. Residue G124, located in the extracellular loop between TM1 and TM2, is conserved across species, and the G124R missense mutation is predicted deleterious with computational tools. To investigate the pathogenicity potential, BK channels were co-expressed with 132WT and 132G124R subunits in HEK293T cells. BK/132 currents were assessed from inside-out patches under physiological K+ conditions (140/ 6 mM K+ and 10 mu M Ca2+) during activation and inactivation (voltage-dependence and kinetics). Using 132 subunits lacking inactivation (132IR) revealed that currents from BK/132IRG124R channels activated 2-fold faster and deactivated 2-fold slower compared with currents from BK/132IRWT channels, with no change in the voltage dependence of activation (V1/2). Despite the changes in the BK channel opening and closing, BK/132G124R inactivation rates (tiinact and tirecovery), and the V1/2 of inactivation, were unaltered compared with BK/132WT channels under standard steady-state voltage protocols. Action potential-evoked current was also unchanged. Thus, the mutant phenotype suggests the 132G124R TM1-TM2 extracellular loop could regulate BK channel activation and deactivation kinetics. However, additional evidence is needed to validate pathogenicity for this patient associated variant in KCNMB2.