Qian X , Nimigean CM , Niu X , Moss BL , Magleby KL .

AR32805 NIAMS NIH HHS , R01 AR032805 NIAMS NIH HHS

	Figure 1. . Schematic diagram of the membrane topology of the β1 and α subunit of the BK (Slo1) channel is shown in the top panel. The core and tail region of the α subunit are indicated as well as the RCK1, RCK2, and serine proteinase (SerP) like domains. The unconserved linker between S8 and S9 connects the core and tail as well as the two RCK domains. The tail contains the Ca2+ bowl with five consecutive aspartic acid residues, implicated with high affinity Ca2+ binding. Schematic diagrams of the channels examined in this study are indicated below the topology diagrams. Note that the linker region between the S8-S9 is missing in the Slo1 core/Slo3 tail channel, and is present in the Slo1 core/Slo3 tail joined channel.
	Figure 2. . The β1 subunit increases the apparent Ca2+ sensitivity of the Slo1core/Slo1 tail channels while reducing the voltage sensitivity. (A and B) Representative single-channel current traces recorded from Slo1 core/Slo1 tail channels with and without β1 subunits for 1.1, 2.5, 5.7 μM Ca2+i, as indicated, at 30 mV. (C and D) Representative macrocurrents recorded for 0 and 20 μM Ca2+i with and without the β1 subunit. For currents with 0 Ca2+i, the potential was held at −80 mV, stepped to potentials between 0 and 300 mV in increments of 20 mV, and then stepped to 40 mV to measure tail currents. For currents with 20 μM Ca2+i, the potential was held at −120 mV, stepped to potentials between −100 to 120 mV in increments of 10 mV and then stepped to −80 mV to measure tail currents. (E) G-V curves derived from tail currents of Slo1core/Slo1 tail channels with and without β1 subunits. Each point plots the mean from >5 different patches. The lines in the GV plots in this and later figures are the fitted Boltzmann function with Eq. 1. The average voltage sensitivity was 20.2 ± 1.0 mV/e-fold without the β1 subunit and 26.3 ± 2.1 mV/e-fold with the β1 (F) Plots of the V0.5 versus Ca2+i for experiments like in (E). V0.5 was determined separately for data from each of >5 different patches and then averaged.
	Figure 3. . The β1 subunit had little effect on burst duration and Po of Slo1 core/Slo3 tail channels at 30 mV, while decreasing the voltage sensitivity. (A and B) Representative single-channel currents recorded from Slo1core/Slo3 tail channels with and without β1 subunits, for 0, 20, and 100 μM Ca2+i at 30 mV. (C and D) Representative macrocurrents recorded with and without β1 subunits, for either 0 or 20 μM Ca2+i. Currents were held at −100 mV and then activated by stepping to potentials between −50 to 200 mV in increments of 10 mV, with tail currents measured at −80 mV. (E) G-V curves derived from tail currents of Slo1core/Slo3 tail channels with and without β1 subunits. The average voltage sensitivity was 22.6 ± 0.4 mV/e-fold without β1 subunits and 28.8 ± 0.5 mV/e-fold with β1 subunits. (F) Plots of V0.5 for Slo1 core/Slo3 tail channels with and without β1 subunits.
	Figure 4. . Comparison of the single-channel kinetics for various channel constructs with and without β1 subunits. Slo1 core/Slo1 tail channels: 2.5 μM Ca2+i. Slo1 core/Slo3 tail channels: 0 μM Ca2+i. Slo1 with D965N mutation: 20 μM Ca2+i. Average of 5–9 patches in each case, except 3 patches for burst duration and gap duration of D965N.
	Figure 5. . DHS-I and estrogen activate Slo1 core/Slo3 tail channels only in the presence of the β1 subunit, indicating that the β1 subunit is functionally associated with Slo1 core/Slo3 tail channels. (A and B) Representative single-channel currents from Slo1core/Slo3 tail channels with and without β1 subunits and 100 nM intracellular DHS-I, as indicated. (C and D) Representative single-channel currents from Slo1core/Slo3 tail channels with and without β1 subunits and 10 μM extracellular 17β-estradiol, as indicated.
	Figure 6. . The β1 subunit greatly increases burst duration and Po, and leftward shifts V0.5 after the Ca2+ bowl mutation D965N to the Slo1 channel. (A) Representative single-channel currents recorded from Slo1 channels, and Slo1 channels with the Ca2+ bowl mutation D965N without, and with β1 subunits. 20 μM Ca2+i, 30 mV. (B) Representative macrocurrents recorded from the D965N mutant Slo1 channels with and without β1 subunits. The potential was held at −120 mV, stepped to potentials between −100 to 200 mV in increments of 10 mV, and then stepped to −80 mV to measure tail currents. (C) G-V curves derived from tail currents of Slo1 channels, D965N mutant Slo1 channels, and D965N mutant Slo1 channels with β1 subunits (20 μM Ca2+i). The average voltage sensitivity was 19.1 ± 0.6 mV/e-fold without the β1 subunit and 23.1 ± 1.2 mV/e-fold with the β1 (n = 5 patches in each case except 3 patches for Slo1). (D) Plots of V0.5 for Slo1 channels, and D965N mutant Slo1 channels without and with β1 subunits.
	Figure 7. . The β1 subunit greatly increases burst duration and Po after a Ca2+ bowl mutation that deletes D965 and D966 of Slo1. (A) Representative single-channel currents recorded from Slo1 channels, and Slo1 channels with the Ca2+ bowl mutation that deletes D965 and D966 without and with β1 subunits. 8 μM Ca2+i, 50 mV. (B) Plots of mean burst duration versus Ca2+i for three mutant channels and four mutant channels with the β1 subunit.

Adelman, Calcium-activated potassium channels expressed from cloned complementary DNAs. 1992, Pubmed, Xenbase

Adelman, Calcium-activated potassium channels expressed from cloned complementary DNAs. 1992, Pubmed , Xenbase
Bao, Elimination of the BK(Ca) channel's high-affinity Ca(2+) sensitivity. 2002, Pubmed , Xenbase
Barrett, Properties of single calcium-activated potassium channels in cultured rat muscle. 1982, Pubmed
Bian, Ca2+-binding activity of a COOH-terminal fragment of the Drosophila BK channel involved in Ca2+-dependent activation. 2001, Pubmed
Braun, Contribution of potential EF hand motifs to the calcium-dependent gating of a mouse brain large conductance, calcium-sensitive K(+) channel. 2001, Pubmed
Brenner, Vasoregulation by the beta1 subunit of the calcium-activated potassium channel. 2000, Pubmed
Brenner, Cloning and functional characterization of novel large conductance calcium-activated potassium channel beta subunits, hKCNMB3 and hKCNMB4. 2000, Pubmed
Butler, mSlo, a complex mouse gene encoding "maxi" calcium-activated potassium channels. 1993, Pubmed , Xenbase
Chang, Differential expression of the alpha and beta subunits of the large-conductance calcium-activated potassium channel: implication for channel diversity. 1997, Pubmed
Cox, Role of the beta1 subunit in large-conductance Ca(2+)-activated K(+) channel gating energetics. Mechanisms of enhanced Ca(2+) sensitivity. 2000, Pubmed , Xenbase
Cui, Allosteric linkage between voltage and Ca(2+)-dependent activation of BK-type mslo1 K(+) channels. 2000, Pubmed
Cui, Intrinsic voltage dependence and Ca2+ regulation of mslo large conductance Ca-activated K+ channels. 1997, Pubmed , Xenbase
Díaz, Role of the S4 segment in a voltage-dependent calcium-sensitive potassium (hSlo) channel. 1998, Pubmed , Xenbase
Dick, (Xeno)estrogen sensitivity of smooth muscle BK channels conferred by the regulatory beta1 subunit: a study of beta1 knockout mice. 2001, Pubmed
Dworetzky, Phenotypic alteration of a human BK (hSlo) channel by hSlobeta subunit coexpression: changes in blocker sensitivity, activation/relaxation and inactivation kinetics, and protein kinase A modulation. 1996, Pubmed
Fettiplace, Mechanisms of hair cell tuning. 1999, Pubmed
Giangiacomo, Mechanism of maxi-K channel activation by dehydrosoyasaponin-I. 1998, Pubmed
Hamill, Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. 1981, Pubmed
Horrigan, Allosteric voltage gating of potassium channels II. Mslo channel gating charge movement in the absence of Ca(2+). 1999, Pubmed
Horrigan, Allosteric voltage gating of potassium channels I. Mslo ionic currents in the absence of Ca(2+). 1999, Pubmed , Xenbase
Jiang, Structure of the RCK domain from the E. coli K+ channel and demonstration of its presence in the human BK channel. 2001, Pubmed , Xenbase
Jiang, Crystal structure and mechanism of a calcium-gated potassium channel. 2002, Pubmed
Jiang, The open pore conformation of potassium channels. 2002, Pubmed
Jiang, Human and rodent MaxiK channel beta-subunit genes: cloning and characterization. 1999, Pubmed
Krause, Xenopus laevis oocytes contain endogenous large conductance Ca2(+)-activated K+ channels. 1996, Pubmed , Xenbase
Latorre, Reconstitution in planar lipid bilayers of a Ca2+-dependent K+ channel from transverse tubule membranes isolated from rabbit skeletal muscle. 1982, Pubmed
Magleby, Burst kinetics of single calcium-activated potassium channels in cultured rat muscle. 1983, Pubmed
Magleby, Kinetic gating mechanisms for BK channels: when complexity leads to simplicity. 2001, Pubmed
Marty, Ca-dependent K channels with large unitary conductance in chromaffin cell membranes. 1981, Pubmed
McManus, Kinetic states and modes of single large-conductance calcium-activated potassium channels in cultured rat skeletal muscle. 1988, Pubmed
McManus, Sampling, log binning, fitting, and plotting durations of open and shut intervals from single channels and the effects of noise. 1987, Pubmed
McManus, Accounting for the Ca(2+)-dependent kinetics of single large-conductance Ca(2+)-activated K+ channels in rat skeletal muscle. 1991, Pubmed
McManus, An activator of calcium-dependent potassium channels isolated from a medicinal herb. 1993, Pubmed
McManus, Functional role of the beta subunit of high conductance calcium-activated potassium channels. 1995, Pubmed , Xenbase
Meera, Large conductance voltage- and calcium-dependent K+ channel, a distinct member of voltage-dependent ion channels with seven N-terminal transmembrane segments (S0-S6), an extracellular N terminus, and an intracellular (S9-S10) C terminus. 1997, Pubmed
Meera, A calcium switch for the functional coupling between alpha (hslo) and beta subunits (Kv,cabeta) of maxi K channels. 1996, Pubmed
Meera, A neuronal beta subunit (KCNMB4) makes the large conductance, voltage- and Ca2+-activated K+ channel resistant to charybdotoxin and iberiotoxin. 2000, Pubmed , Xenbase
Moczydlowski, Bovine pancreatic trypsin inhibitor as a probe of large conductance Ca(2+)-activated K+ channels at an internal site of interaction. 1992, Pubmed
Moss, Gating and conductance properties of BK channels are modulated by the S9-S10 tail domain of the alpha subunit. A study of mSlo1 and mSlo3 wild-type and chimeric channels. 2001, Pubmed , Xenbase
Moss, Hypothesis for a serine proteinase-like domain at the COOH terminus of Slowpoke calcium-activated potassium channels. 1996, Pubmed
Moss, An evolutionarily conserved binding site for serine proteinase inhibitors in large conductance calcium-activated potassium channels. 1996, Pubmed
Nimigean, Functional coupling of the beta(1) subunit to the large conductance Ca(2+)-activated K(+) channel in the absence of Ca(2+). Increased Ca(2+) sensitivity from a Ca(2+)-independent mechanism. 2000, Pubmed
Nimigean, The beta subunit increases the Ca2+ sensitivity of large conductance Ca2+-activated potassium channels by retaining the gating in the bursting states. 1999, Pubmed
Niu, Stepwise contribution of each subunit to the cooperative activation of BK channels by Ca2+. 2002, Pubmed
Pallanck, Cloning and characterization of human and mouse homologs of the Drosophila calcium-activated potassium channel gene, slowpoke. 1994, Pubmed
Pallotta, Single channel recordings of Ca2+-activated K+ currents in rat muscle cell culture. 1981, Pubmed
Petkov, Beta1-subunit of the Ca2+-activated K+ channel regulates contractile activity of mouse urinary bladder smooth muscle. 2001, Pubmed
Plüger, Mice with disrupted BK channel beta1 subunit gene feature abnormal Ca(2+) spark/STOC coupling and elevated blood pressure. 2000, Pubmed
Ramanathan, beta subunits modulate alternatively spliced, large conductance, calcium-activated potassium channels of avian hair cells. 2000, Pubmed
Robitaille, Functional colocalization of calcium and calcium-gated potassium channels in control of transmitter release. 1993, Pubmed
Rothberg, Voltage and Ca2+ activation of single large-conductance Ca2+-activated K+ channels described by a two-tiered allosteric gating mechanism. 2000, Pubmed
Rothberg, Gating kinetics of single large-conductance Ca2+-activated K+ channels in high Ca2+ suggest a two-tiered allosteric gating mechanism. 1999, Pubmed
Ruiz, The single-channel dose-response relation is consistently steep for rod cyclic nucleotide-gated channels: implications for the interpretation of macroscopic dose-response relations. 1999, Pubmed , Xenbase
Schreiber, A novel calcium-sensing domain in the BK channel. 1997, Pubmed , Xenbase
Schreiber, Slo3, a novel pH-sensitive K+ channel from mammalian spermatocytes. 1998, Pubmed
Schreiber, Transplantable sites confer calcium sensitivity to BK channels. 1999, Pubmed , Xenbase
Shi, Intracellular Mg(2+) enhances the function of BK-type Ca(2+)-activated K(+) channels. 2001, Pubmed , Xenbase
Silberberg, Wanderlust kinetics and variable Ca(2+)-sensitivity of dSlo [correction of Drosophila], a large conductance CA(2+)-activated K+ channel, expressed in oocytes. 1996, Pubmed , Xenbase
Tanaka, Molecular constituents of maxi KCa channels in human coronary smooth muscle: predominant alpha + beta subunit complexes. 1997, Pubmed , Xenbase
Valverde, Acute activation of Maxi-K channels (hSlo) by estradiol binding to the beta subunit. 1999, Pubmed , Xenbase
Wallner, Determinant for beta-subunit regulation in high-conductance voltage-activated and Ca(2+)-sensitive K+ channels: an additional transmembrane region at the N terminus. 1996, Pubmed
Wallner, Molecular basis of fast inactivation in voltage and Ca2+-activated K+ channels: a transmembrane beta-subunit homolog. 1999, Pubmed , Xenbase
Wei, Calcium sensitivity of BK-type KCa channels determined by a separable domain. 1994, Pubmed
Weiger, A novel nervous system beta subunit that downregulates human large conductance calcium-dependent potassium channels. 2000, Pubmed
Xia, Rectification and rapid activation at low Ca2+ of Ca2+-activated, voltage-dependent BK currents: consequences of rapid inactivation by a novel beta subunit. 2000, Pubmed , Xenbase
Xia, Multiple regulatory sites in large-conductance calcium-activated potassium channels. 2002, Pubmed
Yang, Block of stretch-activated ion channels in Xenopus oocytes by gadolinium and calcium ions. 1989, Pubmed , Xenbase
Zhang, Allosteric regulation of BK channel gating by Ca(2+) and Mg(2+) through a nonselective, low affinity divalent cation site. 2001, Pubmed , Xenbase