Genetic activation of BK currents in vivo generates bidirectional effects on neuronal excitability

• Published in: Proceedings of the National Academy of Sciences - PNAS 2012-11, Vol.109 (46), p.18997-19002
• Main Authors: Montgomery, Jenna R, Meredith, Andrea L
• Format: Article
• Language: English
• Subjects: Action Potentials; agonists; Amino Acid Substitution; Animals; Base Sequence; Behavioral neuroscience; Biological Sciences; calcium; Circadian rhythm; Disease Models, Animal; Electric potential; electric power; Gene expression; genes; Genetics; HEK293 Cells; heterologous gene expression; Humans; hypothalamus; Ion Channel Gating; Kinetics; Large conductance calcium activated potassium channels; Large-Conductance Calcium-Activated Potassium Channels - genetics; Large-Conductance Calcium-Activated Potassium Channels - metabolism; Mental Disorders - genetics; Mental Disorders - metabolism; Mental Disorders - pathology; Mental Disorders - physiopathology; Mice; Mice, Transgenic; Molecular Sequence Data; muscles; Mutation, Missense; Neurons; Neurons - metabolism; Neurons - pathology; Neuropsychology; Period Circadian Proteins - genetics; Period Circadian Proteins - metabolism; potassium channels; Rodents; seizures; smooth muscle; Suprachiasmatic Nucleus - metabolism; Suprachiasmatic Nucleus - pathology; Suprachiasmatic Nucleus - physiopathology; Transgenes; Transgenic animals; Waveforms
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1205573109

Large-conductance calcium-activated potassium channels (BK) are potent negative regulators of excitability in neurons and muscle, and increasing BK current is a novel therapeutic strategy for neuro- and cardioprotection, disorders of smooth muscle hyperactivity, and several psychiatric diseases. However, in some neurons, enhanced BK current is linked with seizures and paradoxical increases in excitability, potentially complicating the clinical use of agonists. The mechanisms that switch BK influence from inhibitory to excitatory are not well defined. Here we investigate this dichotomy using a gain-of-function subunit (BK ᴿ²⁰⁷Q) to enhance BK currents. Heterologous expression of BK ᴿ²⁰⁷Q generated currents that activated at physiologically relevant voltages in lower intracellular Ca ²⁺, activated faster, and deactivated slower than wild-type currents. We then used BK ᴿ²⁰⁷Q expression to broadly augment endogenous BK currents in vivo, generating a transgenic mouse from a circadian clock-controlled Period1 gene fragment (Tg-BK ᴿ²⁰⁷Q). The specific impact on excitability was assessed in neurons of the suprachiasmatic nucleus (SCN) in the hypothalamus, a cell type where BK currents regulate spontaneous firing under distinct day and night conditions that are defined by different complements of ionic currents. In the SCN, Tg-BK ᴿ²⁰⁷Q expression converted the endogenous BK current to fast-activating, while maintaining similar current-voltage properties between day and night. Alteration of BK currents in Tg-BK ᴿ²⁰⁷Q SCN neurons increased firing at night but decreased firing during the day, demonstrating that BK currents generate bidirectional effects on neuronal firing under distinct conditions.