-
Duane Allen,
Shin Nakayama,
Masayuki Kuroiwa,
Takaaki Nakano,
Julie Palmateer,
Yasuharu Kosaka,
Carmen Ballesteros,
Masahiko Watanabe,
Chris T Bond,
Rafael Luján,
James Maylie,
John P Adelman,
Paco S Herson
[show abstract]
[hide abstract]
ABSTRACT: In mouse hippocampal CA1 pyramidal neurons, the activity of synaptic small-conductance Ca(2+)-activated K(+) channels type 2 (SK2 channels) provides a negative feedback on N-methyl-D-aspartate receptors (NMDARs), reestablishing Mg(2+) block that reduces Ca(2+) influx. The well-established role of NMDARs in ischemia-induced excitotoxicity led us to test the neuroprotective effect of modulating SK2 channel activity following cerebral ischemia induced by cardiac arrest and cardiopulmonary resuscitation (CA/CPR). Administration of the SK channel positive modulator, 1-ethyl-benzimidazolinone (1-EBIO), significantly reduced CA1 neuron cell death and improved CA/CPR-induced cognitive outcome. Electrophysiological recordings showed that CA/CPR-induced ischemia caused delayed and sustained reduction of synaptic SK channel activity, and immunoelectron microscopy showed that this is associated with internalization of synaptic SK2 channels, which was prevented by 1-EBIO treatment. These results suggest that increasing SK2 channel activity, or preventing ischemia-induced loss of synaptic SK2 channels, are promising and novel approaches to neuroprotection following cerebral ischemia.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 06/2011; 31(12):2302-12. · 5.46 Impact Factor
-
Duane Allen,
Chris T Bond,
Rafael Luján,
Carmen Ballesteros-Merino,
Mike T Lin,
Kang Wang,
Nathan Klett,
Masahiko Watanabe,
Ryuichi Shigemoto,
Robert W Stackman,
James Maylie,
John P Adelman
[show abstract]
[hide abstract]
ABSTRACT: SK2-containing channels are expressed in the postsynaptic density (PSD) of dendritic spines on mouse hippocampal area CA1 pyramidal neurons and influence synaptic responses, plasticity and learning. The Sk2 gene (also known as Kcnn2) encodes two isoforms that differ only in the length of their N-terminal domains. SK2-long (SK2-L) and SK2-short (SK2-S) are coexpressed in CA1 pyramidal neurons and likely form heteromeric channels. In mice lacking SK2-L (SK2-S only mice), SK2-S-containing channels were expressed in the extrasynaptic membrane, but were excluded from the PSD. The SK channel contribution to excitatory postsynaptic potentials was absent in SK2-S only mice and was restored by SK2-L re-expression. Blocking SK channels increased the amount of long-term potentiation induced in area CA1 in slices from wild-type mice but had no effect in slices from SK2-S only mice. Furthermore, SK2-S only mice outperformed wild-type mice in the novel object recognition task. These results indicate that SK2-L directs synaptic SK2-containing channel expression and is important for normal synaptic signaling, plasticity and learning.
Nature Neuroscience 06/2011; 14(6):744-9. · 15.53 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Currently available optogenetic tools, including microbial light-activated ion channels and transporters, are transforming systems neuroscience by enabling precise remote control of neuronal firing, but they tell us little about the role of indigenous ion channels in controlling neuronal function. Here, we employ a chemical-genetic strategy to engineer light sensitivity into several mammalian K(+) channels that have different gating and modulation properties. These channels provide the means for photoregulating diverse electrophysiological functions. Photosensitivity is conferred on a channel by a tethered ligand photoswitch that contains a cysteine-reactive maleimide (M), a photoisomerizable azobenzene (A), and a quaternary ammonium (Q), a K(+) channel pore blocker. Using mutagenesis, we identify the optimal extracellular cysteine attachment site where MAQ conjugation results in pore blockade when the azobenzene moiety is in the trans but not cis configuration. With this strategy, we have conferred photosensitivity on channels containing Kv1.3 subunits (which control axonal action potential repolarization), Kv3.1 subunits (which contribute to rapid-firing properties of brain neurons), Kv7.2 subunits (which underlie "M-current"), and SK2 subunits (which are Ca(2+)-activated K(+) channels that contribute to synaptic responses). These light-regulated channels may be overexpressed in genetically targeted neurons or substituted for native channels with gene knockin technology to enable precise optopharmacological manipulation of channel function.
Journal of Neurophysiology 04/2011; 106(1):488-96. · 3.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Small-conductance Ca2+-activated K+ (SK) channels are widely expressed in neuronal tissues where they underlie post-spike hyperpolarizations, regulate spike-frequency adaptation, and shape synaptic responses. SK channels constitutively interact with calmodulin (CaM), which serves as Ca2+ sensor, and with protein kinase CK2 and protein phosphatase 2A, which modulate their Ca2+ gating. By recording coupled activities of Ca2+ and SK2 channels, we showed that SK2 channels can be inhibited by neurotransmitters independently of changes in the activity of the priming Ca2+ channels. This inhibition involvesSK2-associated CK2 and results from a 3-fold reduction in the Ca2+ sensitivity of channel gating. CK2phosphorylated SK2-bound CaM but not KCNQ2-bound CaM, thereby selectively regulating SK2 channels. We extended these observations to sensory neurons by showing that noradrenaline inhibits SK current and increases neuronal excitability in aCK2-dependent fashion. Hence, neurotransmitter-initiated signaling cascades can dynamically regulate Ca2+ sensitivity of SK channels and directly influence somatic excitability.
Neuron 09/2008; 59(3):439-49. · 14.74 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Small conductance Ca2+-activated K+ channels (SK channels) are complexes of four alpha pore-forming subunits each bound by calmodulin (CaM) that mediate Ca2+ gating. Proteomic analysis indicated that SK2 channels also bind protein kinase CK2 (CK2) and protein phosphatase 2A (PP2A). Coexpression of SK2 with the CaM phosphorylation surrogate CaM(T80D) suggested that the apparent Ca2+ sensitivity of SK2 channels is reduced by CK2 phosphorylation of SK2-bound CaM. By using 4,5,6,7-tetrabromo-2-azabenzimidazole, a CK2-specific inhibitor, we confirmed that SK2 channels coassemble with CK2. PP2A also binds to SK2 channels and counterbalances the effects of CK2, as shown by coexpression of a dominant-negative mutant PP2A as well as a mutant SK2 channel no longer able to bind PP2A. In vitro binding studies have revealed interactions between the N and C termini of the channel subunits as well as interactions among CK2 alpha and beta subunits, PP2A, and distinct domains of the channel. In the channel complex, lysine residue 121 within the N-terminal domain of the channel activates SK2-bound CK2, and phosphorylation of CaM is state dependent, occurring only when the channels are closed. The effects of CK2 and PP2A indicate that native SK2 channels are multiprotein complexes that contain constitutively associated CaM, both subunits of CK2, and at least two different subunits of PP2A. The results also show that the Ca2+ sensitivity of SK2 channels is regulated in a dynamic manner, directly through CK2 and PP2A, and indirectly by Ca2+ itself via the state dependence of CaM phosphorylation by CK2.
Journal of Neuroscience 03/2007; 27(9):2369-76. · 7.11 Impact Factor
