Biophysical and biochemical properties of Slo2.1, an intracellular sodium-activated potassium channel

Slo2.1 channel is a large conductance Na+-activated K + channel which is activated by internal Na+ in a concentration-dependent fashion. In this study, I reported fenamates, such as niflumic acid (NFA), can activate S1o2.1 channel by extracellular application, even in the presence of physiological [Na+]i concentration. The NFA effects of Slo2.1 are concentration-dependent with EC50 = 2.08 mM. Higher concentrations of NFA shifted V1/2 of Slo2.1 activation to more negative potentials, and attenuated the voltage dependence in high [K +]e solution. Extracellular monovalent cations can modulate the S1o2.1 activation. For example, elevation of [K+] e inhibits the channel activities and shifts activation curve to positive, whereas decreased [Na+]e reduces the maximum slope conductance. In addition, the Slo2.1 activation was not appreciably changed by neutralization of charged residues in S1-S4 domains, indicating the weak voltage-dependence of Slo2.1 is not mediated by these domains.;Additionally, biochemical methods revealed that both Slo2.1 and Nav1.5 channels can associate with synapse-associated protein 97 (SAP97), suggesting a SAP97 mediated sodium channel---Na+-activated K + channel coupling system, in which Slo2.1 channel could be activated by Na+ ions conducted from proximate activated Nav channels in vivo.;Collectively, this study reveals some primary biophysical properties of Slo2.1 channel.;Crystal structural and functional studies demonstrated that the activation gate of Kv channel is located at the intracellular entrance, which is formed by S6 bundle crossing. In Shaker channel, V478 defined a narrowest region at the intracellular activation gate. Mutation of the equivalent residue A278 in Slo2.1 to tryptophan results in a nonconducting channel by hydrophobic seal, but A278R mutation failed to exhibit a fully opening phenotype by like-charge repulsion, suggesting that multiple narrow regions in the pore participate in the limit of ion flux. Based on studying result, selectivity filter-mediated gating was proposed for Slo2.1 channel. Besides, S4-S5 linker was found to potentially couple with S6 bundle crossing to affect the gating process.