Two-pore domain potassium (K 2P ) channel expression is believed to underlie the developmental emergence of a potassium leak conductance [I K(SO) ] in cerebellar granule neurons (CGNs), suggesting that K 2P function is an important determinant of the input conductance and resting membrane potential. To investigate the role that different K 2P channels may play in the regulation of CGN excitability, we generated a mouse lacking TASK-1, a K 2P channel known to have high expression levels in CGNs. In situ hybridization and real-time PCR studies in wild-type and TASK-1 knock-outs (KOs) demonstrated that the expression of other K 2P channels was unaltered in CGNs. TASK-1 knock-out mice were healthy and bred normally but exhibited compromised motor performance consistent with altered cerebellar function. Whole-cell recordings from adult cerebellar slice preparations revealed that the resting excitability of mature CGNs was no different in TASK-1 KO and littermate controls. However, the modulation of I K(SO) by extracellular Zn 2ϩ , ruthenium red, and H ϩ was altered. The I K(SO) recorded from TASK-1 knock-out CGNs was no longer sensitive to alkalization and was blocked by Zn 2ϩ and ruthenium red. These results suggest that a TASK-1-containing channel population has been replaced by a homodimeric TASK-3 population in the TASK-1 knock-out. These data directly demonstrate that TASK-1 channels contribute to the properties of I K(SO) in adult CGNs. However, TASK channel subunit composition does not alter the resting excitability of CGNs but does influence sensitivity to endogenous modulators such as Zn 2ϩ and H ϩ .

The ability of neurons, such as cerebellar granule neurons (CGNs), to fire action potentials (APs) at high frequencies during sustained depolarization is usually explained in relation to the functional properties of voltage-gated ion channels. Two-pore domain potassium (K 2P ) channels are considered to simply hyperpolarize the resting membrane potential (RMP) by increasing the potassium permeability of the membrane. However, we find that CGNs lacking the TASK-3 type K 2P channel exhibit marked accommodation of action potential firing. The accommodation phenotype was not associated with any change in the functional properties of the underlying voltage-gated sodium channels, nor could it be explained by the more depolarized RMP that resulted from TASK-3 channel deletion. A functional rescue, involving the introduction of a nonlinear leak conductance with a dynamic current clamp, was able to restore wild-type firing properties to adult TASK-3 knock-out CGNs. Thus, in addition to the accepted role of TASK-3 channels in limiting neuronal excitability, by increasing the resting potassium conductance TASK-3 channels also increase excitability by supporting high-frequency firing once AP threshold is reached.

The TASK-3 channel is an acid-sensitive two-pore-domain K ϩ channel, widely expressed in the brain and probably involved in regulating numerous neuronal populations. Here, we characterized the behavioral and pharmacological phenotypes of TASK-3 knockout (KO) mice. Circadian locomotor activity measurements revealed that the nocturnal activity of the TASK-3 KO mice was increased by 38% (P Ͻ 0.01) compared with wild-type littermate controls, light phase activity being similar. Although TASK-3 channels are abundant in cerebellar granule cells, the KO mice performed as well as the wild-type mice in walking on a rotating rod or along a 1.2-cm-diameter beam. However, they fell more frequently from a narrower 0.8-cm beam. The KO mice showed impaired working memory in the spontaneous alternation task, with the alternation percentage being 62 Ϯ 3% for the wild-type mice and 48 Ϯ 4% (P Ͻ 0.05) for the KO mice. Likewise, during training for the Morris watermaze spatial memory task, the KO mice were slower to find the hidden platform, and in the probe trial, the female KO mice visited fewer times the platform quadrant than the male KO and wild-type mice. In pharmacological tests, the TASK-3 KO mice showed reduced sensitivity to the inhalation anesthetic halothane and the cannabinoid receptor agonist WIN55212-2nylmethanone mesylate] but unaltered responses to the ␣2 adrenoceptor agonist dexmedetomidine, the i.v. anesthetic propofol, the opioid receptor agonist morphine, and the local anesthetic lidocaine. Overall, our results suggest important contributions of TASK-3 channels in the neuronal circuits regulating circadian rhythms, cognitive functions, and mediating specific pharmacological effects.The TASK-3 (K 2P 9.1, KCNK9, KT3.2) channel is an acidsensitive member of the two-pore-domain background K ϩ (K 2P ) channel family (Chapman et al., 2000;Kim et al., 2000;Rajan et al., 2000;Vega-Saenz De Miera et al., 2001). K 2P channels contribute to the resting membrane potential by allowing K ϩ to leak out of the cell. Opening of TASK channels promotes hyperpolarization, whereas their inhibition leads to depolarization (for review, see Goldstein et al., 2001;Bayliss et al., 2003). Native TASK-like currents have been recorded from, e.g., cerebellar granule cells (Millar et al., 2000;Aller et al., 2005;Brickley et al., 2007), hippocampal principal neurons and inhibitory interneurons (Taverna et al., 2005;Torborg et al., 2006), cholinergic cells in the caudateputamen (Berg and Bayliss, 2007), thalamocortical relay neurons (Meuth et al., 2006), hypothalamic orexin/hypocretin neurons (Burdakov et al., 2006), and brainstem noradrenergic, serotonergic, and motor neurons Talley et al., 2000;Washburn et al., 2002).Diverse neurotransmitters (e.g., acetylcholine, serotonin, noradrenaline, and glutamate) and hormones (e.g., thyro- ABBREVIATIONS: K 2P , two-pore-domain background K ϩ channel; WIN55212-2 mesylate, (R)-(ϩ)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylat...

Rhythmic physiology is central to retinal function and survival and adapts vision to daily light intensity changes. Mammalian retina rhythmically releases melatonin when cultured under constant conditions, and the occurrence of clock gene [e.g., Period (Per)] expression has been shown for most cellular layers. However, contribution of the distinct layers to genesis of circadian rhythms within the retina is still debated. To characterize their endogenous oscillatory capacity and their communication at the whole-tissue level, we used a vibratome-based method to isolate individual or paired retina cellular layers from the mPer2Luc mouse and Per1-luciferase (Per1-Luc) rat, and realtime recorded bioluminescence. We report that each layer of the mouse retina harbors a self-sustained oscillator whose period is significantly longer (∼26 hours) than in whole-retina explants (∼22.9 hours), indicating that the period is correlated with the degree of coupling. Accordingly, the maximal period (∼29 hours) is reached upon complete enzymatic dissociation of the retina. By using pharmacological approaches, we demonstrate that connection between retina oscillators involves gap junctions but only minor contribution from the main retina neurochemicals. Taken together with results from Per1-Luc rats, these data show that mammalian retina consists of a network of layer-specific oscillators whose period is determined by their connectivity.