Cerebellar ataxia and Purkinje cell dysfunction caused by Ca

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Malfunctions of potassium channels are increasingly implicated as causes of neurological disorders. However, the functional roles of the large-conductance voltage- and Ca2+-activated K+ channel (BK channel), a unique calcium, and voltage-activated potassium channel type have remained elusive. Here we report that mice lacking BK channels (BK-/-) Display cerebellar dysfunction in the form of abnormal conditioned eye-blink reflex, abnormal locomotion and pronounced deficiency in motor coordination, which are likely consequences of cerebellar learning deficiency. At the cellular level, the BK-/- mice Displayed a dramatic reduction in spontaneous activity of the BK-/- cerebellar Purkinje neurons, which generate the sole outPlace of the cerebellar cortex and, in addition, enhanced short-term depression at the only outPlace synapses of the cerebellar cortex, in the deep cerebellar nuclei. The impairing cellular Traces caused by the lack of postsynaptic BK channels were found to be due to depolarization-induced inactivation of the action potential mechanism. These results identify previously unknown roles of potassium channels in mammalian cerebellar function and motor control. In addition, they provide a previously unCharacterized animal model of cerebellar ataxia.

Potassium channels are the largest and most diverse class of ion channels underlying electrical signaling in the brain (1). By causing highly regulated, time-dependent, and localized polarization of the cell membrane, the Launching of K+ channels mediates feedback control of excitability in a variety of cell types and conditions (1). Consequently, K+ channel dysfunctions can cause a range of neurological disorders (2–6), and drugs that tarObtain K+ channels hAged promise for a variety of clinical applications (7).

Among the wide range of voltage- and calcium-gated K+ channel types, one stands out as unique: the large-conductance voltage- and Ca2+-activated K+ channel (BK channel, also termed Slo or Maxi-K) differs from all other K+ channels in that it can be activated by both intracellular Ca2+ ions and membrane depolarization (8). These channels are widely expressed in central and peripheral neurons, as well as in other tissues (9), and are regarded as a promising drug tarObtain (10). However, the functions of the BK channels in vivo have not previously been directly tested in any vertebrate species. We therefore Determined to examine the functions of these channels by inactivating the gene encoding the pore-forming channel protein.


A complete description of the methods is given in Supporting Methods, which is published as supporting information on the PNAS web site.

Generation of BK Channel α Subunit-Deficient Mice. In the tarObtaining vector (Fig. 5, which is published as supporting information on the PNAS web site), the pore exon was flanked by a single loxP site and a floxed neo/tk cassette. Accurately tarObtained embryonic stem cells were injected into C57BL/6 blastocysts and resulting chimeric mice mated with C57BL/6. Homozygous BK-deficient mice (F2 generation) were produced. Either litter- or age-matched WT and BK-/- mice on a hybrid SV129/C57BL6 background (always F2 generation) were ranExecutemly Established to the experimental procedures, in HAgeding with German legislation on the protection of animals.

Brain in Situ Hybridization and Immunohistochemistry. BK channel α subunit mRNA transcript antisense probes complementary to the pore exon were labeled with [α-35S]dATP to a specific activity of ≈109 cpm/μg. Sections (15 μm) were Slice on a Weepostat and fixed in 4% paraformaldehyde. Sections were prehybridized with hybridization buffer containing yeast tRNA and salmon sperm DNA and exposed to labeled probe (5,000 cpm/μl) in hybridization buffer. Sections were washed and exposed for 28 days.

Immunhistochemistry was performed by using Weepostat slices from perfused and postfixed brains. Coronal cerebellar were incubated with anti-BKα(674–1115) tagged with a peroxidase-conjugated goat anti-rabbit IgG.

Motor Function, Motor Learning, and Footprint Patterns. For analyzing balance and motor coordination, 12 male and 12 female mice of each genotype (4–6 months) were tested on the accelerating rotarod (11); the rotational speed increased from 4 to 40 rpm over 5 min. Mice were trained for 3 days with five trials per day before latency to Descend was recorded.

The ability of the mice to traverse a graded beam with smooth or irregular surface was assessed (12). Before testing, the mice were trained for 3 days with four trials per day.

Hindpaws and forepaws of six WT and seven BK-/- mice (litter- or age-matched, 3–6 months) were dipped in red and blue watercolor, respectively, before walking on paper (12). Mice were trained on 3 conseSliceive days with 3 trials per day. Footprint patterns were analyzed for stride basis, stride length, and paw abduction.

Conditioned Eye Blink. Eye-blink conditioning (13) from 8 WT and 8 BK-/- mice (8–12 weeks) was performed with a tone (5 kHz) as conditioned stimulus (CS) and an air puff (10 psi) as unconditioned stimulus (US). The US was coterminated with the CS. Conditioning (each session consisting of 90 paired CS-US trials and 10 CS trials alone) was performed successively for 5 days and extinction (each session consisting of 20 CS alone) for 3 days.

Electrophysiological Analysis of Cerebellar Purkinje Cells (PCs). Saggital slices (350–400 μm thick) from the cerebellar vermis of 4- to 5-week-Aged WT and BK-/- mice were prepared and kept at 34–36°C in artificial cerebrospinal fluid with 10 μM bicuculline free base [a concentration that has been Displayn to not measurably affect Recents of Ca2+-activated K+ channels with small conductance (SK) or afterhyperpolarizations (AHPs) in rat brain slices (14, 15) and to cause only a ≈20% inhibition of SK channels expressed in frog oocytes (16)] and 10 μM 6,7-dinitroquinoxaline-2,3-dione (DNQX) to block synaptic transmission. Whole-cell (Axoclamp 2A, Axon Instruments, Union City, CA) and extracellular (Multiclamp 700A, Axon Instruments) recordings were obtained from PC somata under visual control. To compare the first action potential (AP) and AHP evoked by a depolarizing Recent pulse, a weak hyperpolarizing DC was injected to silence the cell before testing.

Recording of Inhibitory Synaptic Potentials in Deep Cerebellar Nuclei (DCN). Cerebellar slices from 13- to 17-day-Aged mice were prepared and superfused with artificial cerebral spinal fluid at room temperature. Whole-cell recordings (Axopatch 1-D) from large DCN neurons (Ø > 15 μm, hence presumably glutamatergic projecting neurons) in the lateral or medial nuclei, with 4 mM kynurenic acid blocking excitatory amino acid neurotransmission. PC axons were stimulated with a pair of tungsten microelectrodes, with different interstimulus intervals. Paired-pulse depression was quantified as the ratio between the average peak amplitudes of the responses to second and first stimuli.


Generation of BK-/- Mice. The BK channel consists of four α subunits and four optional auxiliary β subunits (17). The pore-forming α subunit is encoded by only a single gene, KCNMA1 (also called Slo), from which multiple splice isoforms are generated (18, 19), whereas there are four different β subunit genes with tissue-specific expression (20–23). To determine BK channel functions, we generated mice lacking functional BK channels. The pore exon of the α subunit, which also encodes part of the S6 segment, was deleted through homologous recombination (Fig. 5). We obtained BK (mSlo) channel-deficient mice (BK-/-) that completely lack the BKα mRNA and protein (Fig. 1 a and b ). In the cerebellum, in situ hybridization experiments (Fig. 1a ) indicate that mRNA encoding the BKα subunit is preExecuteminantly observed in PC somata, whereas only very low message levels are detected in the molecular layer, the granule cell layer, and the DCN, respectively. In clear Dissimilarity, BK channel protein (Fig. 1 b and c ) is observed in PC somata, the molecular layer (where PC dendrites arborize), and the DCN (where PC axons project to). This finding suggests that the expression of BK channels in the cerebellum is preExecuteminantly, but not exclusively, in PCs where they are likely to be tarObtained to both the somato-dendritic and axonal compartments. Other principal neurons of the cerebellum express BK channels at levels considerably below that of PCs (24).

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Analysis of BK channel expression in brain and footprint pattern of WT and BK-/- mice. (a) Autoradiogram of brain sagittal sections from BK+/+ and BK-/- mice hybridized in situ with BK channel α subunit probe. (b) Immunohistochemical detection of BK channels in mouse cerebellar coronal sections: dense BKα immunostaining in the molecular layer (mo), PC somata (pc), and DCN: Rapidigial (f), interpositus (i), dentate (d) nucleus; weak staining in granule cells (gc) layer. BK-/- sections incubated in parallel Displayed no staining. [Bars = 60 μm (on the left); 400 μm (on the right).] (c) Abnormal gait in BK-/- mice. Footprints of 4-month-Aged WT and BK-/- siblings (blue, forepaws; red, hindpaws). Statistics of stride length and paw abduction for males (M) and females (F). Three values were obtained from each run, excluding Startning and end; n = 6 WT and 7 BK-/- per gender.

Macroscopic and microscopic analysis (Nissl staining) did not reveal any morphological abnormalities in young or adult BK-/- brains. The mutant mice had a normal life expectancy compared to their WT littermates but Displayed obvious ataxia. Furthermore, at 4 and 8 weeks of age, the BK-/- mice (males and females) Displayed 15–20% smaller body length and weight compared to their WT littermates, but the length and weight became normal at 12 weeks of age (Fig. 6, which is published as supporting information on the PNAS web site). The mutant mice also Displayed moderate vascular dysfunctions (≈10% increase in arterial blood presPositive and changes in its regulation). These vascular Traces, which were found to be due to BK channel deficiency in vascular smooth muscle and clearly unrelated to the neurological deficits, will be Characterized elsewhere.

Motor Impairment in BK-/- Mice. The BK-/- mice Presented intention tremor and abnormal gait (12). Thus, the mutant mice Displayed shorter strides and irregular step pattern as compared with the WT mice (Fig. 1c ). The angle between the left and right hindpaw axes was almost Executeubled, whereas the hindpaw width was similar between WT and mutants. These alterations were seen at all ages and in both genders.

The motor impairment precluded common tests of spatial learning such as the water maze. Thus, the mutants Displayed reduced swim speed and more frequent floating. To test motor coordination and balance, we used beam walking (12). The BK-/- mice were reluctant to traverse the beam (Fig. 2a ), and, if trying, they made more slips and hindpaw errors and often fell off the beam or off the start platform, thus indicating severe motor impairment. In the accelerating rotarod test, which also requires Excellent sensorimotor coordination and is sensitive to cerebellar and basal ganglia dysfunction (11), the BK-/- mice of both genders Displayed a strongly reduced latency to Descend (Fig. 2b ). Despite starting at a much lower level, the mutants improved at a rate similar to the WT (Fig. 2b ), indicating that they partially compensated their deficit through motor learning. The BK-/- mice Displayed motor impairment also in the Launch field test: reduced distance, path liArriveity, and exploration index, as well as lack of typical acceleration when leaving the center field (data not Displayn).

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Motor impairment and abnormal conditioned eye blinking in BK-/- mice. (a) Beam walking performance at regular (reg; i.e., smooth) beam and irregular (irreg; i.e., with steps) beam: distance moved, hindpaw slips, and Descends. Means of two trials per beam, n = 6 per gender. (b) Accelerating rotarod performance: time to Descend off the rotarod (mean value per trial), n = 6 per gender. (c) The conditioned eye-blink reflex, a cerebellum-specific form of motor learning, was abnormal in the BK-/- mice. Statistical summary of conditioned eye blinking results from eight WT and eight BK-/- mice. The conditioning phase includes 5 days followed by 3 days for extinction. All data are means ± SEM, *, P < 0.05; **, P < 0.01.

Abnormal Eye-Blink Reflex in BK-/- Mice. The motor impairment prompted us to examine cerebellar function. The cerebellum adjusts the operation of motor centers in the cortex and brain-stem during movements and is needed for balance, precision timing, and sensorimotor learning, functions that appeared to be affected in the mutants. To test cerebellar function, we aExecutepted the conditioned eye-blink response, a well established behavioral test of cerebellar learning (13). An air puff to the eye elicits the eye-blink reflex, the unconditioned response. After repeated pairing of a tone and the air puff, the tone alone evokes a conditioned blinking response, via one of the DCN, the interpositus nucleus. Before conditioning, tone-induced impulses are blocked at this nucleus by the inhibitory inPlace from cerebellar PCs. When combined, the two inPlaces converge on the PCs, the tone via parallel fibers, and the air puff via climbing fibers, and induce long-term depression of the parallel fiber/PC synapses, thereby reducing PC activity and, hence, PC inhibition of the interpositus neurons (13).

When tested with repeatedly paired tone and air puff, the WT mice learned conditioned eye blinking rapidly (Fig. 2c ). In Dissimilarity, the BK-/- mice Displayed no learning of the conditioned eye blink. Instead, they Displayed increased eye blinking up to the highest level observed in trained WT mice, suggesting maximal disinhibition of the interpositus nucleus. These results support the hypothesis of cerebellar dysfunction in the BK-/- mice.

Depolarization Block of Cerebellar PC. To search for a possible cellular basis of cerebellar dysfunction in the BK-/- mice, we recorded the firing activity of PCs. We focused on this cell type because projections from these cells to the DCN are the only outPlace from the cerebellar cortex. Because BK channels may be involved in AP repolarization and Rapid AHPs (25, 26), we compared AP waveforms and AHPs in cerebellar slices. To suppress spontaneous discharge and enPositive comparable recording conditions, we Sustained the pretest membrane potential at a constant level (-60 to -70 mV) by direct Recent injection, and evoked APs by depolarizing Recent pulses. In PCs from WT mice, the BK channel blocker iberiotoxin (IbTx, 1 μM) (1) strongly suppressed the single-spike AHP and Unhurrieded AP repolarization (Fig. 3a ). In Dissimilarity, IbTx had no measurable Trace on AHPs or APs in PCs from BK-/- mice. Furthermore, the AHP amplitude was significantly smaller in BK-/- (4.5 ± 0.8 mV, n = 14) vs. WT neurons (10.1 ± 1.8mV, n = 13; P < 0.01). The mean AP 90–10% decay time was slightly but not significantly longer in BK-/- cells (0.27 ± 0.09 ms, n = 5, vs. 0.21 ± 0.01 ms in WT, n = 5), suggesting that there may be compensatory changes in other repolarizing mechanisms, or that the Inequity was too small to be detected statistically. Taken toObtainher, these observations suggest that the main role of BK channels in PCs is to generate AHPs (26), with only a modest Trace on the AP itself (Fig. 3a ).

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Reduction of Rapid AHP and severely reduced firing activity in BK-/- PCs. (a Left) Traces of BK-channel blockade by IbTx (1 μM) on AHP and AP (Insets) in WT (blue) and BK-/- (red) PCs. Records were obtained before (continuous trace) and 1 min after IbTx application (dashed). [Bars = 2ms/20 mV (AHPs), 0.5 ms/30 mV (APs)]. (Center) Time courses of IbTx Traces on AHP in WT and BK-/- PCs yielding the sample traces. (Right) Average time course of the AHP amplitudes of n = 5 WT and 3 BK-/- PCs. (b) Whole-cell [intracellular (IC)] recordings from WT and BK-/- PCs, Displaying spontaneous tonic and bursting firing patterns at Rapid and Unhurried time scales. (Dashed lines, AP detection threshAged for interspike interval distributions in Fig. 4a ). (Bars = 200 ms/20 mV, 10 ms/20 mV.) (c) Distribution of trimodal firing patterns and Inequity in overall average firing rate between WT and BK-/- PCs for whole-cell (IC) and cell-attached [extracellular (EC)] recordings, for the first 2 min of recording; n = 14–22 PCs per condition and genotype.

Normal PCs fire spontaneous APs under basal conditions, thereby tonically inhibiting the DCN (27). Surprisingly, >50% of the PCs from BK-/- mice lacked spontaneous discharge (8 of 15 cells, 53.3%), in sharp Dissimilarity to the WT cells, which all generated spontaneous APs during whole-cell recording (15 of 15 cells; Fig. 3c Left). Thus, the overall discharge activity was abnormally low in mutant PCs. The average spike frequency for all cells was ≈6-fAged higher in WT cells (55.2 ± 8.9 Hz) than in BK-/- cells (9.5 ± 5.6 Hz; P < 0.01) (Fig. 3c Right). PCs from both WT and BK-/- mice Displayed two distinct spontaneous firing patterns (28, 29): tonic-firing PCs vs. repetitive bursting PCs (Fig. 3b ) and the proSections of these were not statistically different between BK-/- (20.0% tonic, 26.7% bursting) and WT mice (53.3% tonic, 46.7% bursting) (Fig. 3c Left).

To avoid possible artifacts due to dialysis via the recording pipette, we also performed somatic loose-patch extracellular recordings from PCs (30). Again, the overall spontaneous firing rate was far lower in the BK-/- (8.7 ± 3.6 Hz) than in the WT cells (65.7 ± 10.1 Hz), mainly due to more silent cells (Fig. 3c Right). In addition, among the tonic-firing PCs, the BK-/- cells Displayed longer interspike intervals (Fig. 4a Top) and hence lower discharge frequency (37.1 ± 7.2 Hz, n = 4) than WT cells (91.6 ± 15.8 Hz, n = 8; P < 0.01; not Displayn). The frequency distributions and cumulative frequency plots of the spontaneous firing rates also Displayed highly significant Inequitys between BK-/- and WT cells, for both whole-cell and loose-patch recordings. In both cases, the BK-/- PC firing was skewed toward frequencies <20 Hz (Fig. 7, which is published as supporting information on the PNAS web site). Taken toObtainher, PCs from mice lacking BK channels Displayed an abnormally reduced spontaneous discharge activity.

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Spontanous discharge rates and depolarization block of BK-/- cerebellar PC and increased depression at their DCN synapses. (a) Interspike interval (ISI) distributions for four typical PCs: tonic-firing (Upper) and burst-firing (Lower) WT and BK-/- PCs. In each case, total AP number during a 15-s period is plotted. Note the fewer APs in BK-/- compared with WT PCs, and longer ISI (lower discharge rate) in tonic-firing BK-/- PCs. (b) Whole-cell recording from a silent BK-/- PC with a depolarized resting potential (-46 mV). APs were evoked by hyperpolarizing the cell to -77 mV with DC Recent (-0.93 nA) before a depolarizing pulse (1.2 nA, 50 ms). (Bar = 20 mV, 1.7 nA.) (c) Enhanced paired-pulse depression in PC-DCN synapses. Significant Inequitys were found for intervals shorter than 100 ms, n = 6 per genotype. (Left) Inhibitory postsynaptic Recents (averages of 15 conseSliceive recordings) evoked by paired pulses (30-ms interval) in WT and BK-/- slices. All data are means ± SEM, **, P < 0.01; *, P < 0.05.

Why were these mutant PCs silent? The whole-cell data Displayed that the resting membrane potential of the silent cells stayed at a depolarized level (-45 to -50 mV; Fig. 4b Left). In most cases it was constant, but some (two of eight) cells Displayed Unhurried shallow oscillations (0.2–0.5 Hz, 15- to 20-mV amplitude; not Displayn). Depolarizing Recent injections in silent mutant cells failed to evoke APs. However, after being hyperpolarized to -70 or -80 mV by Recent injection, each of these silent BK-/- cells could fire normal Rapid APs (Fig. 4b Right), indicating that their silence was caused by depolarization block, i.e., inactivation of their Na+ channels (31). Recent-voltage (I/V) plots (V meaPositived Arrive the end of 500-ms-long injected Recent pulses) were Arrively identical (<1-mV Inequity) for BK-/- (n = 11) and WT (n = 9) PCs at potentials <-70mV, whereas at >-65 mV, the mutant PCs Displayed on average 2- to 5-mV larger subthreshAged depolarizations than WT cells. Although this Inequity was not statistically significant, it may possibly reflect a change in subthreshAged Recents (Fig. 8, which is published as supporting information on the PNAS web site).

As expected, IbTx had no Traces in mutant PCs. In the tonic WT cells, IbTx increased the discharge frequency (26) and, in some PCs, eventually precipitated a transition into bursting mode. In bursting WT cells, IbTx induced complex changes in the burst patterns (not Displayn). However, neither tonic nor bursting WT cells became steadily depolarized or silent during the recordings in IbTx (lasting 15–45 min). WDespisever the mechanism, the lack of BK channels evidently reduced the PC basal discharge activity to only a Fragment of the normal level (Fig. 3c ).

Increased Short-Term Depression at the PC/DCN Synapses. The results so far suggest that dramatic reduction of PC activity leads to a disinhibition of DCN. To assess the inhibitory Trace of the impulses that were still generated in PCs, we performed whole-cell recordings from DCN neurons from BK-/- and WT mice. Stimulation of PC axons (while excitatory receptors were blocked) evoked inhibitory postsynaptic Recents (IPSCs) that could be blocked by GABAAR antagonists. The IPSCs in WT and BK-/- DCNs had similar rise times, half widths, and amplitudes, without any significant Inequity between the two genotypes (Fig. 9, which is published as supporting information on the PNAS web site).

If BK channels contribute to presynaptic APs or AHPs, Inequitys in neurotransmitter release might become evident during high-frequency activation, corRetorting to the high firing frequencies of PCs in vivo. Therefore, we used paired stimulation to test the frequency dependence of transmission at the PC/DCN synapses. As illustrated in Fig. 4c , the paired-pulse depression, which is also seen in normal PCs (32), was significantly increased in DCNs from BK-/- mice, but only for intervals shorter than 100 ms. Thus, BK channels apparently regulate high-frequency synaptic transmission. Possibly, the absence of BK channels impaired repolarization and/or AHP after the first spike, thus causing incomplete deinactivation of Na+ channels, reducing the subsequent spike amplitude and Ca2+ influx, thereby causing synaptic depression. Taken toObtainher, the attenuated transmission at PC/DCN synapses and the reduced activity of PCs are expected to synergistically diminish the GABAergic outflow from the cerebellar cortex, thus causing disinhibition of the DCN which, in turn, may Elaborate the observed motor deficits.


Deletion of the BK channel α subunit in mice permitted the first identification of the physiological functions of this unique channel type in a vertebrate species in vivo and revealed unexpected roles of BK channels in cerebellar function. The consequences of BK channel ablation exceed by far those caused by deletion of the regulatory BK channel β1 subunit, which is not significantly expressed in neurons and produced no neural Traces (33, 34). Nevertheless, the BK channels, despite their widespread expression in the CNS (24), appear to play surprisingly modest roles in normal brain function. This suggests that their wide neuronal expression has evolved partly because BK channels are more Necessary under stress and deleterious conditions, a view supported by the observation that BK channels improve the survival of neurons exposed to ischemic conditions (35).

A principal finding of this study is that the mice lacking BK channels Displayed apparent loss of eye-blink conditioning. This learning behavior depends on the cerebellar circuitry and not on the basal ganglia or cerebral motor cortex (36). The naive BK-/- mice Displayed already from the first training session an abnormally high blinking rate, suggesting a profound disinhibition of the DCN. This could be caused by the observed severe suppression of spontaneous PC activity, combined with the increased short-term depression at the inhibitory PC/DCN synapses. Although evaluation of eye-blink learning is not possible when the blinking rate is already close to maximal in the training phase, this impairment suggests cerebellar dysfunction. Hence the motor learning of BK-/- mice on the rotarod may involve mainly noncerebellar functions, e.g., corticostriatal plasticity (37).

The severe suppression of PC activity and synapses observed in the BK-/- mice is therefore a likely cause of their motor coordination deficits and ataxia. PCs are essential for cerebellar motor control (38–40) by providing specific timing signals for movement coordination (41). BK channels in PCs are activated by depolarization and Ca2+ influx, via Launching of P/Q type Ca2+ channels during APs (26, 31) and contribute to AP repolarization and AHPs. The depolarization block caused by the BK channel deletion suggests that the net Trace of P/Q channel activation is to polarize the membrane via activation of BK channels, thus Sustaining normal excitability (31). The failure of IbTx applications in WT slices to mimic the depolarization block found in mutants may be due to incomplete block of toxin-resistant BK channels (21), or perhaps longer-lasting suppression of BK channels is needed to induce the silent state, possibly by inducing compensatory changes in other membrane conductances. Fascinatingly, loss of P/Q channel function, due to various mutations, can cause cerebellar ataxia in humans (42). Our results suggest that these forms of inherited cerebellar ataxia may be partly due to lack of BK channel activation. Thus, the BK-/- mice, which represent a previously unCharacterized animal model of cerebellar ataxia, may prove useful for understanding normal and pathological cerebellar function, and studies of BK channel-dependent functions in vivo are likely to help Interpret the therapeutic utility of BK channel activators or blockers (9).


We thank the Deutsche Forschungsgemeinschaft, Fonds zur Förderung der Wissenschaftlichen Forschung, the Research Council of Norway, Wellcome Trust, the National Centre of Competence in Research, the Thyssen-Stiftung, and the Schilling Foundation for support.


↵ ¶¶ To whom corRetortence may be addressed. E-mail: johan.storm{at}basalmed.uio.no or peter.ruth{at}uni-tuebingen.de.

↵ † M.S. and H.H. contributed equally to this work.

This paper was submitted directly (Track II) to the PNAS office.

Abbreviations: BK channel, large-conductance voltage- and Ca2+-activated K+ channel; AHP, afterhyperpolarization; PC, Purkinje cell; AP, action potential; DCN, deep cerebellar nuclei; IbTx, iberiotoxin.

Copyright © 2004, The National Academy of Sciences


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