Polymorphism of ADAM12, DPP6 and PRKN genes and their associations with milk production traits in Holstein

Milk production traits as the most important economic traits of dairy cows, they directly reflect the benefits of breeding and the economic benefits of pasture. In this study, A disintegrin and metalloproteinase-12 (ADAM12), Parkinson's disease gene 2 (PRKN) and dipeptidyl peptidase-like protein subtype 6 (DPP6) polymorphism in 384 Chinese Holstein cows were detected by time-of-flight mass spectrometry and through statistical analysis using software such as Popgene 32, SAS 9.4 and Origin 2022, the relationship between single nucleotide polymorphisms (SNPs) of three genes with four milk production traits such as daily milk yield (DMY), milk fat percentage (MFP), milk protein percentage (MPP) and somatic cell score (SCS) was verified at molecular level. The results showed that four polymorphic loci (116,467,133, 116,604,487, 116,618,268 and 116,835,111) of DPP6 gene, two polymorphic loci (97,665,052 and 97,159,837) of PRKN gene and two polymorphic loci (45,542,714 and 45,553,888) of ADAM12 gene were detected. PRKN-97665052, DPP6-116467133, ADAM12-45553888, DPP6-116604487 and DPP6-116835111 were all in Hardy-Weinberg equilibrium state (p > .05). ADAM12-45542714, PRKN-97159837 and PRKN-97665052 were moderately polymorphic (0.25 ≤ PIC <0.50) in Holstein. It is evident that the selection potential and genetic variation of these five loci are relatively large, and the genetic richness is relatively high. The correlation analysis of different genotypes between these eight loci and milk production traits of Holstein showed that ADAM12-45542714 and DPP6-116835111 (p < .01) had an extremely significant effects on the DMY of Chinese Holstein in Ningxia, while PRKN-97665052 had an extremely significant effect on MFP (p < .01). The effect of PRKN-97665052 and DPP6-116467133 on MPP of Holstein were extremely significant (p < .01). DPP6-116618268 had an extremely significant effect on the SCS of Holstein in Ningxia (p < .01), and AA genotype individuals showed a higher SCS than GG genotype individuals; the other two loci (ADAM12-45553888 and DPP6-116604487) had no significant effects on milk production traits of Holstein (p > .05). In addition, through the joint analysis of DPP6, PRKN and ADAM12 gene loci, it was found that the interaction effect between the three gene loci could significantly affect the DMY, SCS (p < .01) and MPP (p < .05). In conclusion, several different loci of DPP6, PRKN and ADAM12 genes can affect the milk production traits of Holstein to different degrees. PRKN, DPP6 and ADAM12 genes can be used as potential candidate genes for milk production traits of Holstein for marker-assisted selection, providing theoretical basis for breeding of Holstein.

LILBID and nESI: Different Native Mass Spectrometry Techniques as Tools in Structural Biology

Native mass spectrometry is applied for the investigation of proteins and protein complexes worldwide. The challenge in native mass spectrometry is maintaining the features of the proteins of interest, such as oligomeric state, bound ligands, or the conformation of the protein complex, during transfer from solution to gas phase. This is an essential prerequisite to allow conclusions about the solution state protein complex, based on the gas phase measurements. Therefore, soft ionization techniques are required. Widely used for the analysis of protein complexes are nanoelectro spray ionization (nESI) mass spectrometers. A newer ionization method is laser induced liquid bead ion desorption (LILBID), which is based on the release of protein complexes from solution phase via infrared (IR) laser desorption. We use both methods in our lab, depending on the requirements of the biological system we are interested in. Here we benchmark the performance of our LILBID mass spectrometer in comparison to a nESI instrument, regarding sample conditions, buffer and additive tolerances, dissociation mechanism and applicability towards soluble and membrane protein complexes. Graphical Abstract ᅟ.

[Autoimmune encephalitis due to mantle cell lymphoma]

BACKGROUND

Autoimmune encephalitis is a rare condition characterized by subacute development of cognitive and psychiatric symptoms. A paraneoplastic syndrome involves autoimmune encephalitis caused by classic antibodies. Although this condition is often associated with cancer, no malignancy has yet been found in 70-90% of patients at the time of diagnosis.

CASE DESCRIPTION

We saw a 58-year-old male patient with fatigue, diarrhoea and weight loss. He was also experiencing hyperekplexia, personality changes and an instable gait. PET-CT revealed generalised lymphadenopathy. Histopathological analysis of a lymph node showed mantle cell lymphoma. Further investigation of the fluid revealed anti-DPPX IgG antibodies. We treated the patient's mantle cell lymphoma with R-CHOP; he achieved complete remission and his neurological symptoms resolved almost completely.

CONCLUSION

The presence of anti-DPPX IgG antibodies is rare. Although it has not been proven that these antibodies are related to malignancies, this is the third of 30 known cases in which anti-DPPX IgG antibodies and a lymphatic malignancy were found.

The cardiomyocyte molecular clock regulates the circadian expression of Kcnh2 and contributes to ventricular repolarization

BACKGROUND

Sudden cardiac death (SCD) follows a diurnal variation. Data suggest the timing of SCD is influenced by circadian (~24-hour) changes in neurohumoral and cardiomyocyte-specific regulation of the heart's electrical properties. The basic helix-loop-helix transcription factors brain muscle arnt-like1 (BMAL1) and circadian locomotor output control kaput (CLOCK) coordinate the circadian expression of select genes.

OBJECTIVE

We sought to test whether Bmal1 expression in cardiomyocytes contributes to K(+) channel expression and diurnal changes in ventricular repolarization.

METHODS

We used transgenic mice that allow for the inducible cardiomyocyte-specific deletion of Bmal1 (iCSΔBmal1(-/-)). We used quantitative polymerase chain reaction, voltage clamping, promoter-reporter bioluminescence assays, and electrocardiographic telemetry.

RESULTS

Although several K(+) channel gene transcripts were downregulated in iCSΔBmal1(-/-)mouse hearts, only Kcnh2 exhibited a robust circadian pattern of expression that was disrupted in iCSΔBmal1(-/-) hearts. Kcnh2 underlies the rapidly activating delayed-rectifier K(+) current, and the rapidly activating delayed-rectifier K(+) current recorded from iCSΔBmal1(-/-) ventricular cardiomyocytes was ~50% smaller than control ventricular myocytes. Promoter-reporter assays demonstrated that the human Kcnh2 promoter is transactivated by the coexpression of BMAL1 and CLOCK. Electrocardiographic analysis showed that iCSΔBmal1(-/-) mice developed a prolongation in the heart rate-corrected QT interval during the light (resting) phase. This was secondary to an augmented circadian rhythm in the uncorrected QT interval without a corresponding change in the RR interval.

CONCLUSION

The molecular clock in the heart regulates the circadian expression of Kcnh2, modifies K(+) channel gene expression, and is important for normal ventricular repolarization. Disruption of the cardiomyocyte circadian clock mechanism likely unmasks diurnal changes in ventricular repolarization that could contribute to an increased risk of cardiac arrhythmias/SCD.

Decreased expression of hyperpolarisation-activated cyclic nucleotide-gated channel 3 in Hirschsprung’s disease

AIM: To determine if hyperpolarisation-activated nucleotide-gated (HCN) channels exist in human colon, and to investigate the expression of HCN channels in Hirschsprung’s disease.

METHODS: We investigated HCN1, HCN2, HCN3 and HCN4 protein expression in pull-through specimens from patients with Hirschsprung’s disease (HSCR, n = 10) using the proximal-most ganglionic segment and distal-most aganglionic segment, as well as in healthy control specimens obtained at the time of sigmoid colostomy closure in children who had undergone anorectoplasty for imperforate anus (n = 10). Fluorescent immunohistochemistry was performed to assess protein distribution, which was then visualized using confocal microscopy.

RESULTS: No HCN1 channel expression was observed in any of the tissues studied. Both HCN2 and HCN4 proteins were found to be equally expressed in the aganglionic and ganglionic bowel in HSCR and controls. HCN3 channel expression was found to be markedly decreased in the aganglionic colon vs ganglionic colon and controls. HCN2-4 channels were seen to be expressed within neurons of the myenteric and submucosal plexus of the ganglionic bowel and normal controls, and also co-localised to interstitial cells of Cajal in all tissues studied.

CONCLUSION: We demonstrate HCN channel expression in human colon for the first time. Reduced HCN3 expression in aganglionic bowel suggests its potential role in HSCR pathophysiology.

Diet-induced obesity impairs endothelium-derived hyperpolarization via altered potassium channel signaling mechanisms

Background

The vascular endothelium plays a critical role in the control of blood flow. Altered endothelium-mediated vasodilator and vasoconstrictor mechanisms underlie key aspects of cardiovascular disease, including those in obesity. Whilst the mechanism of nitric oxide (NO)-mediated vasodilation has been extensively studied in obesity, little is known about the impact of obesity on vasodilation to the endothelium-derived hyperpolarization (EDH) mechanism; which predominates in smaller resistance vessels and is characterized in this study.

Methodology/Principal Findings

Membrane potential, vessel diameter and luminal pressure were recorded in 4^th order mesenteric arteries with pressure-induced myogenic tone, in control and diet-induced obese rats. Obesity, reflecting that of human dietary etiology, was induced with a cafeteria-style diet (∼30 kJ, fat) over 16–20 weeks. Age and sexed matched controls received standard chow (∼12 kJ, fat). Channel protein distribution, expression and vessel morphology were determined using immunohistochemistry, Western blotting and ultrastructural techniques. In control and obese rat vessels, acetylcholine-mediated EDH was abolished by small and intermediate conductance calcium-activated potassium channel (SK_Ca/IK_Ca) inhibition; with such activity being impaired in obesity. SK_Ca-IK_Ca activation with cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA) and 1-ethyl-2-benzimidazolinone (1-EBIO), respectively, hyperpolarized and relaxed vessels from control and obese rats. IK_Ca-mediated EDH contribution was increased in obesity, and associated with altered IK_Ca distribution and elevated expression. In contrast, the SK_Ca-dependent-EDH component was reduced in obesity. Inward-rectifying potassium channel (K_ir) and Na⁺/K⁺-ATPase inhibition by barium/ouabain, respectively, attenuated and abolished EDH in arteries from control and obese rats, respectively; reflecting differential K_ir expression and distribution. Although changes in medial properties occurred, obesity had no effect on myoendothelial gap junction density.

Conclusion/Significance

In obese rats, vasodilation to EDH is impaired due to changes in the underlying potassium channel signaling mechanisms. Whilst myoendothelial gap junction density is unchanged in arteries of obese compared to control, increased IK_Ca and Na⁺/K⁺-ATPase, and decreased K_ir underlie changes in the EDH mechanism.

A novel potassium channel in photosynthetic cyanobacteria

Elucidation of the structure-function relationship of a small number of prokaryotic ion channels characterized so far greatly contributed to our knowledge on basic mechanisms of ion conduction. We identified a new potassium channel (SynK) in the genome of the cyanobacterium Synechocystis sp. PCC6803, a photosynthetic model organism. SynK, when expressed in a K⁺-uptake-system deficient E.coli strain, was able to recover growth of these organisms. The protein functions as a potassium selective ion channel when expressed in Chinese Hamster Ovary cells. The location of SynK in cyanobacteria in both thylakoid and plasmamembranes was revealed by immunogold electron microscopy and Western blotting of isolated membrane fractions. SynK seems to be conserved during evolution, giving rise to a TPK (two-pore K⁺ channel) family member which is shown here to be located in the thylakoid membrane of Arabidopsis. Our work characterizes a novel cyanobacterial potassium channel and indicates the molecular nature of the first higher plant thylakoid cation channel, opening the way to functional studies.

Left versus right atrial difference in dominant frequency, K(+) channel transcripts, and fibrosis in patients developing atrial fibrillation after cardiac surgery

BACKGROUND

The development of atrial fibrillation (AF) after cardiac surgery is associated with adverse outcomes; however, the mechanism(s) that trigger and maintain AF in these patients are unknown.

OBJECTIVE

The purpose of this study was to test our hypothesis that postoperative AF is maintained by high-frequency sources in the left atrium (LA) resulting from ion channel and structural features that differ from the right atrium (RA).

METHODS

Forty-four patients with no previous history of AF who underwent cardiac surgery consented to LA and RA biopsies. Histologic sections evaluated fatty infiltration, fibrosis, and iron deposition; quantitative reverse transcription-polymerase chain reaction (RT-PCR) assessed ion channel expression. In a subset of 27 patients, LA and RA unipolar recording leads were also placed. In patients who developed AF, the dominant frequency (DF) for each lead was calculated using fast Fourier transform.

RESULTS

DFs during AF were LA 6.26 +/- 0.8 Hz, RA 4.56 +/- 0.7 Hz (P <.01). RT-PCR revealed LA-to-RA differences in mRNA abundance for Kir2.3 (1.8:1) and Kir3.4 (2.3:1). While LA fibrosis was greater in patients developing AF compared with those remaining in normal sinus rhythm (10.8% +/- 11% vs. 3.8% +/- 3.5%; P = .03), the amount of LA fibrosis inversely correlated with the LA DF.

CONCLUSIONS

This is the first demonstration of LA-to-RA frequency differences during postoperative AF, which are associated with LA-to-RA differences in mRNA levels for potassium channel proteins and LA fibrosis. These results strongly suggest that sources of AF after cardiac surgery are located in the LA and are stabilized by LA fibrosis.

The expression of hyperpolarization activated cyclic nucleotide gated (HCN) channels in the rat ovary are dependent on the type of cell and the reproductive age of the animal: a laboratory investigation

BACKGROUND

Aim of this study was to test the hypothesis that levels of hyperpolarization activated cyclic nucleotide gated channels 1 to 4 (HCN1-4) are linked to the reproductive age of the ovary.

METHODS

Young, adult, and reproductively aged ovaries were collected from Sprague-Dawley rats. RT-PCR and western blot analysis of ovaries was performed to investigate the presence of mRNA and total protein for HCN1-4. Immunohistochemistry with semiquantitative H score analysis was performed using whole ovarian histologic sections.

RESULTS

RT-PCR analysis showed the presence of mRNA for HCN1-4. Western blot analysis revealed HCN1-3 proteins in all ages of ovarian tissues. Immunohistochemistry with H score analysis demonstrated distinct age-related changes in patterns of HCN1-3 in the oocytes, granulosa cells, theca cells, and corpora lutea. HCN4 was present only in the oocytes, with declining levels during the reproduction lifespan.

CONCLUSION

The evidence presented here demonstrates cell-type and developmental age patterns of HCN1-4 channel expression in rat ovaries. Based on this, we hypothesize that HCN channels have functional significance in rat ovaries and may have changing roles in reproductive aging.

Local and global effects of I(h) distribution in dendrites of mammalian neurons

The hyperpolarization-activated cation current I(h) exhibits a steep gradient of channel density in dendrites of pyramidal neurons, which is associated with location independence of temporal summation of EPSPs at the soma. In striking contrast, here we show by using dendritic patch-clamp recordings that in cerebellar Purkinje cells, the principal neurons of the cerebellar cortex, I(h) exhibits a uniform dendritic density, while location independence of EPSP summation is observed. Using compartmental modeling in realistic and simplified dendritic geometries, we demonstrate that the dendritic distribution of I(h) only weakly affects the degree of temporal summation at the soma, while having an impact at the dendritic input location. We further analyze the effect of I(h) on temporal summation using cable theory and derive bounds for temporal summation for any spatial distribution of I(h). We show that the total number of I(h) channels, not their distribution, governs the degree of temporal summation of EPSPs. Our findings explain the effect of I(h) on EPSP shape and temporal summation, and suggest that neurons are provided with two independent degrees of freedom for different functions: the total amount of I(h) (controlling the degree of temporal summation of dendritic inputs at the soma) and the dendritic spatial distribution of I(h) (regulating local dendritic processing).

Hyperpolarization-activated channels in trigeminal ganglia innervating healthy and pulp-exposed teeth

AIM

To use immunocytochemistry for determining the expression of HCN1, HCN2 and HCN3 (three subunits of the hyperpolarization-activated cyclic nucleotide-gated current channel) in rodent trigeminal ganglia (TG) that innervate healthy teeth and determine if expression of HCN subunits is increased in TG following pulp exposure.

METHODOLOGY

Pulps were exposed in right maxillary incisors of male Sprague-Dawley rats. After fixation, TG were removed, cryostat sectioned, and immunocytochemistry was utilized to study the expression of HCN1-3 subunits. Immunoreactivity of individual neurons from the maxillary region of the TG was determined with ImageJ software. Differences in the number immunopositive neurons amongst groups were tested for statistical significance with either a Yates or Pearson's chi-square or Fisher's exact probability tests depending on neuron sample size. Differences in the intensity of immunoreactivity between groups were tested for statistical significance with a Student's t-test.

RESULTS

The majority of TG neurons were immunopositive for HCN1-3. Moreover, statistically significant increases in the number of TG neurons immunopositive for HCN1 and the intensity of HCN1-3 immunoreactivity were observed within hours of exposing the tooth pulp.

CONCLUSIONS

HCN1-3 expression, as determined by immunocytochemistry, is increased within hours after injury. Given that I(h) can facilitate neuronal excitability, results of the current study suggest that antagonists to HCN1-3 subunits could work as analgesics in the alleviation of orofacial pain.

ΔF508 Mutation Results in Impaired Gastric Acid Secretion

The cystic fibrosis transmembrane conductance regulator (CFTR) is recognized as a multifunctional protein that is involved in Cl(-) secretion, as well as acting as a regulatory protein. In order for acid secretion to take place a complex interaction of transport proteins and channels must occur at the apical pole of the parietal cell. Included in this process is at least one K(+) and Cl(-) channel, allowing for both recycling of K(+) for the H,K-ATPase, and Cl(-) secretion, necessary for the generation of concentrated HCl in the gastric gland lumen. We have previously shown that an ATP-sensitive potassium channel (K(ATP)) is expressed in parietal cells. In the present study we measured secretagogue-induced acid secretion from wild-type and DeltaF508-deficient mice in isolated gastric glands and whole stomach preparations. Secretagogue-induced acid secretion in wild-type mouse gastric glands could be significantly reduced with either glibenclamide or the specific inhibitor CFTR-inh172. In DeltaF508-deficient mice, however, histamine-induced acid secretion was significantly less than in wild-type mice. Furthermore, immunofluorescent localization of sulfonylurea 1 and 2 failed to show expression of a sulfonylurea receptor in the parietal cell, thus further implicating CFTR as the ATP-binding cassette transporter associated with the K(ATP) channels. These results demonstrate a regulatory role for the CFTR protein in normal gastric acid secretion.

Activating of ATP-dependent K+ channels comprised of K(ir) 6.2 and SUR 2B by PGE2 through EP2 receptor in cultured interstitial cells of Cajal from murine small intestine

The interstitial cells of Cajal (ICC) are pacemaker cells in gastrointestinal tract and generate an electrical rhythm in gastrointestinal muscles. We investigated the possibility that PGE(2) might affect the electrical properties of cultured ICC by activating ATP-dependent K(+) channels and, the EP receptor subtypes and the subunits of ATP-dependent K(+) channels involved in these activities were identified. In addition, the regulation of intracellular Ca(2+) ([Ca(2+)](i)) mobilization may be involved the action of PGE(2) on ICC. Treatments of ICC with PGE(2) inhibited electrical pacemaker activities in the same manner as pinacidil, an ATP-dependent K(+) channel opener and PGE(2) had only a dose-dependent effect. Using RT-PCR technique, we found that ATP-dependent K(+) channels exist in ICC and that these are composed of K(ir) 6.2 and SUR 2B subunits. To characterize the specific membrane EP receptor subtypes in ICC, EP receptor agonists and RT-PCR were used: Butaprost (an EP(2) receptor agonist) showed the actions on pacemaker currents in the same manner as PGE(2). However sulprostone (a mixed EP(1) and EP(3) agonist) had no effects. In addition, RT-PCR results indicated the presence of the EP(2) receptor in ICC. To investigate cAMP involvement in the effects of PGE(2) on ICCs, SQ-22536 (an inhibitor of adenylate cyclase) and cAMP assays were used. SQ-22536 did not affect the effect of PGE(2) on pacemaker currents, and PGE(2) did not stimulate cAMP production. Also, we found PGE(2) inhibited the spontaneous [Ca(2+)](i) oscillations in cultured ICC. These observations indicate that PGE(2) alters pacemaker currents by activating the ATP-dependent K(+) channels comprised of K(ir) 6.2-SUR 2B in ICC and this action of PGE(2) are through EP(2) receptor subtype and also the activation of ATP-dependent K(+) channels involves intracellular Ca(2+) mobilization.

Potassium channel gene expression in the rat cochlear nucleus

Potassium channels play a critical role in defining the electrophysiological properties accounting for the unique response patterns of auditory neurons. Serial analysis of gene expression (SAGE), microarrays, RT-PCR, and real-time RT-PCR were used to generate a broad profile of potassium channel expression in the rat cochlear nucleus. This study identified mRNAs for 51 different potassium channel subunits or channel interacting proteins. The relative expression levels of 27 of these transcripts among the AVCN, PVCN, and DCN were determined by real-time RT-PCR. Four potassium channel transcripts showed substantial levels of differential expression. Kcnc2 was expressed more than 15-fold higher in the DCN as compared to AVCN and PVCN. In contrast, Kcnj13 had an approximate 10-fold higher expression in AVCN and PVCN than in DCN. Two subunits that modify the activity of other channels were inversely expressed between ventral and dorsal divisions. Kcns1 was over 15-fold higher in DCN than AVCN or PVCN, while Kcns3 was about 25-fold higher in AVCN than in DCN. The expression patterns of potassium channels in the subdivisions of the cochlear nucleus provide a basis for understanding the electrophysiological mechanisms which sub-serve central auditory processing and provide targets for further investigations into neural plastic changes that occur with hearing loss.

Organisation of the mouse sinoatrial node: structure and expression of HCN channels

OBJECTIVE

To reveal the structural characteristics of the sinoatrial node (SAN) and the distribution of hyperpolarization-activated cyclic nucleotide-gated cation channels (HCN) in the SAN in the mouse.

METHODS

The structure of the SAN and the distribution of HCN channels in the SAN in the mouse were studied by histology and immunolabelling of ANP, Cx43 and HCN channels.

RESULTS

The mouse SAN is a comma-shaped structure with a length of approximately 1.5 mm parallel to the crista terminalis and is separated from atrial muscle by connective tissue at the border both with the crista terminalis and the atrial septum. A unique compact nodal structure with densely-packed nodal cells was identified at the head of the comma-shaped SAN. Cell size and fibre orientation vary regionally in the SAN: the cells in the compact node are small and are orientated perpendicular to the crista terminalis, whereas the cells in the more inferior part are larger and more loosely-packed and are orientated parallel to the crista terminalis. All SAN cells exhibited labelling of HCN4, but no cell exhibited detectable labelling of HCN1, HCN2, ANP and Cx43, while surrounding atrial cells exhibited labelling of ANP and Cx43, but not HCN1, HCN2 and HCN4. A specialised interface between the SAN and surrounding atrial muscle was also identified: strands of HCN4-positive nodal cells protrude into the atrial muscle and strands of Cx43-positive atrial cells protrude into the SAN; thus, there are interdigitations between the SAN and atrial muscle.

CONCLUSIONS

In the mouse, (i) the SAN is structurally complex with a densely-packed head and loosely-packed tail; (ii) HCN4 is the only HCN isoform detectable and is present throughout the SAN; and (iii) there is a specialised interface between the SAN and surrounding atrium that may be necessary for the SAN to drive the more hyperpolarized atrial muscle.

Actions of ZD0947, a novel ATP-sensitive K+ channel opener, on membrane currents in human detrusor myocytes

BACKGROUND AND PURPOSE

ATP-sensitive K+ channels (K(ATP) channels) play important roles in regulating the resting membrane potential of detrusor smooth muscle. Actions of ZD0947, a novel KATP channel opener, on both carbachol (CCh)-induced detrusor contractions and membrane currents in human urinary bladder myocytes were investigated.

EXPERIMENTAL APPROACH

Tension measurements and patch-clamp techniques were utilized to study the effects of ZD0947 in segments of human urinary bladder. Immunohistochemistry was also performed to detect the expression of the sulphonylurea receptor 1 (SUR1) and the SUR2B antigens in human detrusor muscle.

KEY RESULTS

ZD0947 (> or = 0.1 microM) caused a concentration-dependent relaxation of the CCh-induced contraction of human detrusor, which was reversed by glibenclamide. The rank order of the potency to relax the CCh-induced contraction was pinacidil > ZD0947 > diazoxide. In conventional whole-cell configuration, ZD0947 (> or = 1 microM) caused a concentration-dependent inward K+ current which was suppressed by glibenclamide at -60 mV. When 1 mM ATP was included in the pipette solution, application of pinacidil or ZD0947 caused no inward K+ current at -60 mV. Gliclazide (< or =1 microM), a selective SUR1 blocker, inhibited the ZD0947-induced currents (Ki = 4.0 microM) and the diazoxide-induced currents (high-affinity site, Ki1 = 42.4 nM; low-affinity site, Ki2 = 84.5 microM) at -60 mV. Immunohistochemical studies indicated the presence of SUR1 and SUR2B proteins, which are constituents of KATP channels, in the bundles of human detrusor smooth muscle.

CONCLUSIONS AND IMPLICATIONS

These results suggest that ZD0947 caused a glibenclamide-sensitive detrusor relaxation through activation of glibenclamide-sensitive KATP channels in human urinary bladder.

Pharmacological characteristics of endothelium-derived hyperpolarizing factor-mediated relaxation of small mesenteric arteries from db/db mice

Endothelial dysfunction is considered as a major risk factor of cardiovascular complications of type I and type II diabetes. Our previous studies have demonstrated that endothelial dysfunction in the small mesenteric arteries from 12-16 week old type II diabetic mice was associated with decreased bio-availability of nitric oxide whereas endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation was preserved. The objective of the present study was to characterize EDHF-mediated relaxations of small mesenteric arteries from db/db mice. A depolarizing concentration of KCl or tetraethylammonium (TEA, 10 mM) significantly inhibited the EDHF-mediated relaxation to acetylcholine and bradykinin in small mesenteric arteries from both db/+ and db/db mice. Charybdotoxin or iberiotoxin alone and a combination of ouabain and barium significantly reduced the maximal relaxation to acetylcholine in small mesenteric arteries from db/db mice and charybdotoxin or iberiotoxin either alone or in combination with apamin reduced the sensitivity to the EDHF-mediated component of the relaxation response to bradykinin. 17-octadecynoic acid, but not catalase, significantly reduced the sensitivity to EDHF-mediated responses to bradykinin in db/db mice; 17-octadecynoic acid had no effect on acetylcholine-mediated relaxations. No differences were, however, detected for mRNA expression levels of calcium-activated potassium channels or connexins 37, 40, 43 and 45. Collectively, these data suggest that bradykinin-induced, EDHF-dependent relaxation in small mesenteric arteries from db/db mice is mediated via cytochrome P450 product that activates the large conductance calcium-activated potassium (BK(Ca) or Slo) channel, whereas the acetylcholine-induced, EDHF-mediated relaxation involves neither cytochrome P450 product nor hydrogen peroxide.

Properties of ion channels in rabbit mesenchymal stem cells from bone marrow

The present study was designed to investigate properties of ion channels in undifferentiated rabbit mesenchymal stem cells (MSCs) from bone marrow using whole-cell patch-clamp and RT-PCR techniques. It was found that three types of outward currents were present in rabbit MSCs, including an inward rectifier K(+) current (I(Kir)), a noise-like Ca(2+)-activated K(+) current (I(KCa)) co-present with delayed rectifier K(+) current (IK(DR)). I(Kir) was inhibited by Ba(2+), while I(KCa) was inhibited by paxilline (a blocker of big conductance I(KCa) channels) and clotrimazole (an inhibitor of intermediate conductance I(KCa) channels). IK(DR) exhibited a slow inactivation, "U-shaped" voltage-dependent inactivation, and slow recovery from inactivation, and the current was inhibited by tetraethylammonium or 4-aminopyridine. RT-PCR revealed the molecular identities for the functional ionic currents, including Kir1.1 (possibly responsible for I(Kir)), KCa1.1 and KCa3.1 (possibly responsible for I(KCa)), and Kv1.2, Kv2.1, and Kv2.2 (possibly responsible for IK(DR)). These results demonstrate for the first time that three types of functional ion channel currents (i.e., I(Kir), I(KCa), and IK(DR)) are present in rabbit MSCs from bone marrow.

Hyperpolarization-activated cation channels are expressed in rat hypothalamic gonadotropin-releasing hormone (GnRH) neurons and immortalized GnRH neurons

OBJECTIVES

The current research was conducted to determine whether hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels are expressed in gonadotropin-releasing hormone (GnRH) neurons in the female rat hypothalamus and immortalized GnRH neurons (GT1-7 cells).

METHODS

Double-label fluorescence immunohistochemistry was used to colocalize HCN1-4 channels and GnRH in GnRH neurons in the female rat hypothalamus. Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry were used to analyze HCN channel gene expression in GT1-7 cells.

RESULTS

Double-label fluorescence immunohistochemistry showed that 43% of hypothalamic GnRH neurons immunostained for HCN2 and 90% of GnRH neurons immunostained for HCN3. RT-PCR and Western blot showed expression of all four HCN channel subunits in GT1-7 cells. Double-label immunocytochemistry showed cytoplasmic immunostaining of HCN2 and HCN3 in GT1-7 cells.

CONCLUSIONS

This study demonstrates for the first time that HCN channels are expressed in GnRH neurons in the rat hypothalamus and GT1-7 cells. Our research supports the hypothesis that HCN channels may be involved in electrical bursting activity and pulsatile GnRH secretion in endogenous GnRH neurons and GT1-7 cells.

Imaging of spiking and subthreshold activity of mitral cells with voltage-sensitive dyes

To obtain a more complete description of individual neurons, it is necessary to complement electrical measurements with technologies such as voltage imaging with intracellular dyes, which permit massive parallel recording from many sites on neuronal processes. Utilizing such an approach, we investigate the functional structure of the mitral cell, the principal output neuron in the rat olfactory bulb. These experiments were designed to determine the number, location, and the stability of spike trigger zones, the excitability of terminal dendritic branches, the pattern and nature of spike initiation and propagation in the primary dendrite, the basic characteristics of the evoked EPSPs at the site of origin (the glomerular tuft), and its attenuation along the primary dendrite. The images of spike trigger zones showed that an action potential can be initiated in three different compartments of the mitral cell: the soma-axon region, the primary dendrite trunk, and the terminal dendritic tuft, which appears to be fully excitable. The amplitude of the EPSPs evoked by olfactory nerve stimulation was determined at the site of origin (glomerular tuft) and its attenuation was monitored optically along the entire length of the primary dendrite.

Nodal, paranodal and juxtaparanodal axonal proteins during demyelination and remyelination in multiple sclerosis

Saltatory conduction in myelinated fibres depends on the specific molecular organization of highly specialized axonal domains at the node of Ranvier, the paranodal and the juxtaparanodal regions. Voltage-gated sodium channels (Na(v)) have been shown to be deployed along the naked demyelinated axon in experimental models of CNS demyelination and in multiple sclerosis lesions. Little is known about aggregation of nodal, paranodal and juxtaparanodal constituents during the repair process. We analysed by immunohistochemistry on free-floating sections from multiple sclerosis brains the expression and distribution of nodal (Na(v) channels), paranodal (paranodin/Caspr) and juxtaparanodal (K(v) channels and Caspr2) molecules in demyelinated and remyelinated lesions. Whereas in demyelinated lesions, paranodal and juxtaparanodal proteins are diffusely distributed on denuded axons, the distribution of Na(v) channels is heterogeneous, with a diffuse immunoreactivity but also few broad Na(v) channel aggregates in all demyelinated lesions. In contrast to the demyelinated plaques, all remyelinated lesions are characterized by the detection of aggregates of Na(v) channels, paranodin/Caspr, K(v) channels and Caspr2. Our data suggest that these aggregates precede remyelination, and that Na(v) channel aggregation is the initial event, followed by aggregation of paranodal and then juxtaparanodal axonal proteins. Remyelination takes place in multiple sclerosis tissue but myelin repair is often incomplete, and the reasons for this remyelination deficit are many. We suggest that a defect of Na(v) channel aggregation might be involved in the remyelination failure in demyelinated lesions with spared axons and oligodendroglial cells.

An Abnormal Mitochondrial–Hypoxia Inducible Factor-1α–Kv Channel Pathway Disrupts Oxygen Sensing and Triggers Pulmonary Arterial Hypertension in Fawn Hooded Rats

Background— The cause of pulmonary arterial hypertension (PAH) was investigated in humans and fawn hooded rats (FHR), a spontaneously pulmonary hypertensive strain.

Methods and Results— Serial Doppler echocardiograms and cardiac catheterizations were performed in FHR and FHR/BN1, a consomic control that is genetically identical except for introgression of chromosome 1. PAH began after 20 weeks of age, causing death by &60 weeks. FHR/BN1 did not develop PAH. FHR pulmonary arterial smooth muscle cells (PASMCs) had a rarified reticulum of hyperpolarized mitochondria with reduced expression of electron transport chain components and superoxide dismutase-2. These mitochondrial abnormalities preceded PAH and persisted in culture. Depressed mitochondrial reactive oxygen species (ROS) production caused normoxic activation of hypoxia inducible factor (HIF-1α), which then inhibited expression of oxygen-sensitive, voltage-gated K + channels (eg, Kv1.5). Disruption of this mitochondrial-HIF-Kv pathway impaired oxygen sensing (reducing hypoxic pulmonary vasoconstriction, causing polycythemia), analogous to the pathophysiology of chronically hypoxic Sprague-Dawley rats. Restoring ROS (exogenous H 2 O 2 ) or blocking HIF-1α activation (dominant-negative HIF-1α) restored Kv1.5 expression/function. Dichloroacetate, a mitochondrial pyruvate dehydrogenase kinase inhibitor, corrected the mitochondrial-HIF-Kv pathway in FHR-PAH and human PAH PASMCs. Oral dichloroacetate regressed FHR-PAH and polycythemia, increasing survival. Chromosome 1 genes that were dysregulated in FHRs and relevant to the mitochondria-HIF-Kv pathway included HIF-3α (an HIF-1α repressor), mitochondrial cytochrome c oxidase, and superoxide dismutase-2. Like FHRs, human PAH-PASMCs had dysmorphic, hyperpolarized mitochondria; normoxic HIF-1α activation; and reduced expression/activity of HIF-3α, cytochrome c oxidase, and superoxide dismutase-2.

Conclusions— FHRs have a chromosome 1 abnormality that disrupts a mitochondria-ROS-HIF-Kv pathway, leading to PAH. Similar abnormalities occur in idiopathic human PAH. This study reveals an intersection between oxygen-sensing mechanisms and PAH. The mitochondria-ROS-HIF-Kv pathway offers new targets for PAH therapy.

Similar chloride channels in the connecting tubule and cortical collecting duct of the mouse kidney

Using the patch-clamp technique, we investigated Cl−channels on the basolateral membrane of the connecting tubule (CNT) and cortical collecting duct (CCD). We found a ∼10-pS channel in CNT cell-attached patches. Substitution of sodium gluconate for NaCl in the pipette shifted the reversal potential by +25 mV, whereas N-methyl-d-gluconate chloride had no effect, indicating anion selectivity. On inside-out patches, we determined a selectivity sequence of Cl−> Br−∼ NO3−> F−, which is compatible with that of ClC-K2, a Cl−channel in the distal nephron. In addition, the number of open channels ( NPo) measured in cell-attached patches was significantly increased when Ca2+concentration or pH in the pipette was increased, which is another characteristic of ClC-K. These findings suggest that the basis for this channel is ClC-K2. A similar Cl−channel was found in CCD patches. Because CNT and CCD are heterogeneous tissues, we studied the cellular distribution of the Cl−channel using recording conditions (KCl-rich solution in the pipette) that allowed us to detect simultaneously Cl−channels and inwardly rectifying K+channels. We detected Cl−channels alone in 45% and 42% and K+channels alone in 51% and 58% of CNT and CCD patches, respectively. Cl−and K+channels were recorded simultaneously from two patches (4% of patches) in the CNT and from none of the patches in the CCD. This indicates that Cl−and K+channels are located in different cell types, which we suggest may be the intercalated cells and principal cells, respectively.

Physiological volume regulation by spermatozoa

Maturing spermatozoa passing through the epididymis experience increasing osmolality in the luminal environment and mature cells are stored in fluids hyper-osmotic to serum. When ejaculated into the female tract, they encounter a hypo-osmotic challenge which initiates the process of regulatory volume decrease (RVD). Defects in RVD result in hindrance of mucus penetration in man and failure of utero-tubal passage in mice. Epididymal sperm from the mouse and cynomolgus monkey and ejaculated sperm from man and monkey have been isolated and dispersed in media with osmolalities mimicking those of uterine fluid or cervical mucus. The effects of specific and broad-spectrum ion channel blockers indicate the involvement of separate K+ and Cl- channels as well as organic osmolytes in physiological sperm RVD, with mechanisms developed during epididymal maturation. Western blotting and immuno-cytochemistry identify and localise some of these channels which play a crucial role in fertilisation in vivo and could be targets for post-testicular contraception.

A Na+- and Cl- -activated K+ channel in the thick ascending limb of mouse kidney

This study investigates the presence and properties of Na+-activated K+ (K(Na)) channels in epithelial renal cells. Using real-time PCR on mouse microdissected nephron segments, we show that Slo2.2 mRNA, which encodes for the K(Na) channels of excitable cells, is expressed in the medullary and cortical thick ascending limbs of Henle's loop, but not in the other parts of the nephron. Patch-clamp analysis revealed the presence of a high conductance K+ channel in the basolateral membrane of both the medullary and cortical thick ascending limbs. This channel was highly K+ selective (P(K)/P(Na) approximately 20), its conductance ranged from 140 to 180 pS with subconductance levels, and its current/voltage relationship displayed intermediate, Na+-dependent, inward rectification. Internal Na+ and Cl- activated the channel with 50% effective concentrations (EC50) and Hill coefficients (nH) of 30 +/- 1 mM and 3.9 +/- 0.5 for internal Na+, and 35 +/- 10 mM and 1.3 +/- 0.25 for internal Cl-. Channel activity was unaltered by internal ATP (2 mM) and by internal pH, but clearly decreased when internal free Ca2+ concentration increased. This is the first demonstration of the presence in the epithelial cell membrane of a functional, Na+-activated, large-conductance K+ channel that closely resembles native K(Na) channels of excitable cells. This Slo2.2 type, Na+- and Cl--activated K+ channel is primarily located in the thick ascending limb, a major renal site of transcellular NaCl reabsorption.

Functional effects of naturally occurring KCNJ11 mutations causing neonatal diabetes on cloned cardiac KATP channels

ATP-sensitive K+ (K(ATP)) channels are hetero-octamers of inwardly rectifying K+ channel (Kir6.2) and sulphonylurea receptor subunits (SUR1 in pancreatic beta-cells, SUR2A in heart). Heterozygous gain-of-function mutations in Kir6.2 cause neonatal diabetes, which may be accompanied by epilepsy and developmental delay. However, despite the importance of K(ATP) channels in the heart, patients have no obvious cardiac problems. We examined the effects of adenine nucleotides on K(ATP) channels containing wild-type or mutant (Q52R, R201H) Kir6.2 plus either SUR1 or SUR2A. In the absence of Mg2+, both mutations reduced ATP inhibition of SUR1- and SUR2A-containing channels to similar extents, but when Mg2+ was present ATP blocked mutant channels containing SUR1 much less than SUR2A channels. Mg-nucleotide activation of SUR1, but not SUR2A, channels was markedly increased by the R201H mutation. Both mutations also increased resting whole-cell K(ATP) currents through heterozygous SUR1-containing channels to a greater extent than for heterozygous SUR2A-containing channels. The greater ATP inhibition of mutant Kir6.2/SUR2A than of Kir6.2/SUR1 can explain why gain-of-function Kir6.2 mutations manifest effects in brain and beta-cells but not in the heart.

Single channel properties of hyperpolarization-activated cation currents in acutely dissociated rat hippocampal neurones

The hyperpolarization-activated cation current (I(h)), mediated by HCN channels, contributes to intrinsic neuronal properties, synaptic integration and network rhythmicity. Recent studies have implicated HCN channels in neuropathological conditions including epilepsy. While native HCN channels have been studied at the macroscopic level, the biophysical characteristics of individual neuronal HCN channels have not been described. We characterize, for the first time, single HCN currents of excised inside-out patches from somata of acutely dissociated rat hippocampal CA1 pyramidal cells. Hyperpolarization steps elicited non-inactivating channel openings with an apparent conductance of 9.7 pS, consistent with recent reports of native and recombinant HCN channels. The voltage-dependent P(o) had a V(1/2) of -81 +/- 1.8 mV and slope -13.3 +/- 1.9 mV. Blockers of macroscopic I(h), ZD7288 (50 microM) and CsCl (1 mM), reduced the channel conductance to 8 pS and 8.4 pS, respectively. ZD7288 was slightly more effective in reducing the P(o) at depolarized potentials, whereas CsCl was more efficacious at hyperpolarized potentials. The unitary neuronal HCN channels had voltage-dependent latencies to first channel opening and two open states. As expected, ZD7288 and CsCl increased latencies and decreased the properties of both open states. The major endogenous positive modulator of macroscopic I(h) is cAMP. Application of 8Br-cAMP (10 microM) did not affect conductance (9.4 pS), but did increase P(o) and short and long open times. Thus, sensitivity to I(h) modulators supports the single h-channel identity of these unitary currents. Detailed biophysical analysis of unitary I(h) conductances is likely to help distinguish between homomeric and heteromeric expression of these channels - findings that may be relevant toward the pathophysiology of diseases such as epilepsy.

Studies of ATP-sensitive potassium channels on 6-hydroxydopamine and haloperidol rat models of Parkinson's disease: implications for treating Parkinson's disease?

In the present study, we first investigated the effects of unilateral 6-hydroxydopamine (6-OHDA) lesioning of the substantia nigra pars compacta (SNc) on the expression of subunits of ATP-sensitive potassium channels (KATP channels) in the prefrontal cortex (PFC), striatum and hippocampus of adult rats by utilizing semiquantitative reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry techniques. The results show that Kir6.2 and SUR2 expression in the PFC, Kir6.1, Kir6.2 and SUR1 expression in the striatum, and Kir6.1 and Kir6.2 expression in the hippocampus of injured side increased significantly after unilateral 6-OHDA lesioning of the SNc in rats. Afterward, we studied the effects of iptakalim (Ipt), a novel ATP-sensitive potassium channel opener (KCO), on parkinsonian symptoms, which were induced by acute injection of haloperidol. The results indicate that intraperitoneal injection of Ipt (0.125 mg/kg, 0.25 mg/kg or 0.5 mg/kg) partially alleviated haloperidol-induced catalepsy and hypolocomotion. Even though the observed effects (0.5 mg/kg) are better than those of l-3,4-dihydroxyphenylalanine (L-DOPA) (100 mg/kg), Ipt (0.25 mg/kg) failed to enhance the anti-parkinsonian actions of L-DOPA (100 mg/kg). Our results suggest that KATP channels might be involved in the pathogenesis of Parkinson's disease (PD) induced in an animal model and conceptually support the idea that KATP channels may be new therapeutic targets for PD.

Investigating the putative glycine hinge in Shaker potassium channel

The crystal structure of an open potassium channel reveals a kink in the inner helix that lines the pore (Jiang, Y.X., A. Lee, J.Y. Chen, M. Cadene, B.T. Chait, and R. MacKinnon. 2002. Nature 417:523–526). The putative hinge point is a highly conserved glycine residue. We examined the role of the homologous residue (Gly466) in the S6 transmembrane segment of Shaker potassium channels. The nonfunctional alanine mutant G466A will assemble, albeit poorly, with wild-type (WT) subunits, suppressing functional expression. To test if this glycine residue is critical for activation gating, we did a glycine scan along the S6 segment in the background of G466A. Although all of these double mutants lack the higher-level glycosylation that is characteristic of mature Shaker channels, one (G466A/V467G) is able to generate voltage-dependent potassium current. Surface biotinylation shows that functional and nonfunctional constructs containing G466A express at comparable levels in the plasma membrane. Compared with WT channels, the shifted-glycine mutant has impairments in voltage-dependent channel opening, including a right-shifted activation curve and a decreased rate of activation. The double mutant has relatively normal open-channel properties, except for a decreased affinity for intracellular blockers, a consequence of the loss of the side chain of Val467. Control experiments with the double mutants M440A/G466A and G466A/V467A suggest that the flexibility provided by Gly466 is more important for channel function than its small size. Our results support roles for Gly466 both in biogenesis of the channel and as a hinge in activation gating.

Lack of manifestations of diazoxide/5-hydroxydecanoate-sensitive KATP channel in rat brain nonsynaptosomal mitochondria

Pharmacological modulation of the mitochondrial ATP-sensitive K+ channel (mitoKATP) sensitive to diazoxide and 5-hydroxydecanoate (5-HD) represents an attractive strategy to protect cells against ischaemia/reperfusion- and stroke-related injury. To re-evaluate a functional role for the mitoKATP in brain, we used Percoll-gradient-purified brain nonsynaptosomal mitochondria in a light absorbance assay, in radioisotope measurements of matrix volume, and in measurements of respiration, membrane potential (DeltaPsi) and depolarization-induced K+ efflux. The changes in mitochondrial morphology were evaluated by transmission electron microscopy (TEM). Polyclonal antibodies raised against certain fragments of known sulphonylurea receptor subunits, SUR1 and SUR2, and against different epitopes of K+ inward rectifier subunits Kir 6.1 and Kir 6.2 of the ATP-sensitive K+ channel of the plasma membrane (cellKATP), were employed to detect similar subunits in brain mitochondria. A variety of plausible blockers (ATP, 5-hydroxydecanoate, glibenclamide, tetraphenylphosphonium cation) and openers (diazoxide, pinacidil, chromakalim, minoxidil, testosterone) of the putative mitoKATP were applied to show the role of the channel in regulating matrix volume, respiration, and DeltaPsi and K+ fluxes across the inner mitochondrial membrane. None of the pharmacological agents applied to brain mitochondria in the various assays pinpointed processes that could be unequivocally associated with mitoKATP activity. In addition, immunoblotting analysis did not provide explicit evidence for the presence of the mitoKATP, similar to the cellKATP, in brain mitochondria. On the other hand, the depolarization-evoked release of K+ suppressed by ATP could be re-activated by carboxyatractyloside, an inhibitor of the adenine nucleotide translocase (ANT). Moreover, bongkrekic acid, another inhibitor of the ANT, inhibited K+ efflux similarly to ATP. These observations implicate the ANT in ATP-sensitive K+ transport in brain mitochondria.

K ATP channels of primary human coronary artery endothelial cells consist of a heteromultimeric complex of Kir6.1, Kir6.2, and SUR2B subunits

Functional ATP-sensitive potassium (K(ATP)) channels can be reconstituted by expression of various combinations of different pore-forming subunits (Kir6.1 and Kir6.2) and sulfonylurea receptor (SUR) subunits. Using dominant negative and gene knockout approaches, Kir6.2 subunits have been identified as required pore-forming components of plasmalemmal K(ATP) channels in ventricular myocytes. Previous data obtained in heterologous expression systems suggest that Kir6.1 and Kir6.2 subunits are capable of forming a functional heteromultimeric channel complex. However, until now the existence of such heteromultimeric Kir6.1/Kir6.2 complexes has not been demonstrated for native K(ATP) channels. The primary aim of this study was to identify the molecular composition of native K(ATP) channels in primary human coronary artery endothelial cells (HCAEC) and smooth muscle cells (HCASMC) from human origin. We specifically investigated the potential that heteromultimeric Kir6.1/Kir6.2 channels exist in these cells. Using reverse transcriptase-polymerase chain reaction, we detected the expression of Kir6.1, Kir6.2, and SUR2B in both cell types. Western blotting and immunoprecipitation assays demonstrated the presence of Kir6.1 protein in both HCAEC and HCASMC; however, Kir6.2 protein was only expressed in HCAEC. Interaction between Kir6.1 and Kir6.2 subunits was demonstrated by reciprocal co-immunoprecipitation of these two subunits in HCAEC. Furthermore, Kir6.1 and Kir6.2 were detected in the immunoprecipitate when using an anti-SUR2 antibody. Confocal microscopy imaging demonstrated Kir6.1 and Kir6.2 subunits to co-localize at the cell surface membrane in HCAEC. In conclusion, our data characterize the molecular composition of primary human coronary smooth muscle and endothelial cells. We demonstrate that human coronary endothelial K(ATP) channels consist of a heteromultimeric complex of Kir6.1, Kir6.2, and SUR2B subunits.

Comparison of ion channel distribution and expression in cardiomyocytes of canine pulmonary veins versus left atrium

BACKGROUND

Cardiomyocytes in pulmonary vein (PV) sleeves are important in atrial fibrillation (AF), but underlying mechanisms are poorly understood. Pulmonary veins have different ionic current properties compared to left atrium, with pulmonary vein inward-rectifier currents being smaller and delayed-rectifier currents larger than in left atrium.

METHODS

Expression and distribution of the inward-rectifier subunits Kir2.1 and Kir2.3, the rapid delayed-rectifier alpha-subunit ERG, the slow delayed-rectifier alpha-subunit KvLQT1, the beta-subunit minK, the L-type Ca(2+)-subunit Ca(v)1.2, and the Na(+),Ca(2+)-exchanger were quantified by Western blot on isolated cardiomyocytes and localized by immunohistochemistry in tissue sections obtained from canine hearts.

RESULTS

Western blotting indicated significantly greater expression of ERG (by 28%, P<0.05) and KvLQT1 (by 34%, P<0.05) in pulmonary vein versus left atrial (LA) cardiomyocytes, but smaller Kir2.3 and similar Kir2.1, Ca(v)1.2 and Na(+),Ca(2+)-exchanger expression in PV. Kir2.1 exhibited weak transverse tubular distribution in both regions. Kir2.3 localized to intercalated disks in both regions, and to transverse tubules in left atrium but not pulmonary vein. ERG staining was more intense in pulmonary vein than left atrium, localizing to transverse tubules in both regions and intercalated disks in pulmonary veins. KvLQT1 was more intensely expressed in pulmonary veins, with a transverse tubular and intercalated disk localization, versus a more diffuse signal in left atrium. The Na(+),Ca(2+)-exchanger localized to transverse tubules, plasma membranes and intercalated disks with similar intensity in each region.

CONCLUSIONS

Greater ERG and KvLQT1 abundance in pulmonary vein cardiomyocytes, lower abundance of Kir2.3 in pulmonary veins and differential pulmonary vein subcellular distribution of Kir2.3, ERG and KvLQT1 subunits may contribute to ionic current differences between pulmonary vein and left atrial cardiomyocytes.

Enhanced large intestinal potassium permeability in end-stage renal disease

The capacity of the colon for potassium (K+) secretion increases in end-stage renal disease (ESRD), to the extent that it makes a substantial contribution to K+ homeostasis. This colonic K+ adaptive response may reflect enhanced active K+ secretion, and be associated with an increase in apical membrane K+ permeability. In this study, this hypothesis was tested in patients with normal renal function or ESRD, by evaluating the effect of barium ions (a K+ channel inhibitor) on rectal K+ secretion using a rectal dialysis technique, and the expression of high conductance (BK) K+ channel protein in colonic mucosa by immunohistochemistry. Under basal conditions, rectal K+ secretion was almost threefold greater (p < 0.02) in ESRD patients (n = 8) than in patients with normal renal function (n = 10). Intraluminal barium (5 mmol/l) decreased K+ secretion in the ESRD patients by 45% (p < 0.05), but had no effect on K+ transport in patients with normal renal function. Immunostaining using a specific antibody to the BK channel alpha-subunit revealed greater (p < 0.001) levels of BK channel protein expression in surface colonocytes and crypt cells in ESRD patients (n = 9) than in patients with normal renal function (n = 9), in whom low levels of expression were mainly restricted to surface colonocytes. In conclusion, these results suggest that enhanced colonic K+ secretion in ESRD involves an increase in the apical K+ permeability of the large intestinal epithelium, which most likely reflects increased expression of apical BK channels.

A unique role for Kv3 voltage-gated potassium channels in starburst amacrine cell signaling in mouse retina

Direction-selective retinal ganglion cells show an increased activity evoked by light stimuli moving in the preferred direction. This selectivity is governed by direction-selective inhibition from starburst amacrine cells occurring during stimulus movement in the opposite or null direction. To understand the intrinsic membrane properties of starburst cells responsible for direction-selective GABA release, we performed whole-cell recordings from starburst cells in mouse retina. Voltage-clamp recordings revealed prominent voltage-dependent K(+) currents. The currents were mostly blocked by 1 mm TEA, activated rapidly at voltages more positive than -20 mV, and deactivated quickly, properties reminiscent of the currents carried by the Kv3 subfamily of K+ channels. Immunoblots confirmed the presence of Kv3.1 and Kv3.2 proteins in retina and immunohistochemistry revealed their expression in starburst cell somata and dendrites. The Kv3-like current in starburst cells was absent in Kv3.1-Kv3.2 knock-out mice. Current-clamp recordings showed that the fast activation of the Kv3 channels provides a voltage-dependent shunt that limits depolarization of the soma to potentials more positive than -20 mV. This provides a mechanism likely to contribute to the electrical isolation of individual starburst cell dendrites, a property thought essential for direction selectivity. This function of Kv3 channels differs from that in other neurons where they facilitate high-frequency repetitive firing. Moreover, we found a gradient in the intensity of Kv3.1b immunolabeling favoring proximal regions of starburst cells. We hypothesize that this Kv3 channel gradient contributes to the preference for centrifugal signal flow in dendrites underlying direction-selective GABA release from starburst amacrine cells

Putative glucosensing property in rat and human activated microglia

Microglial cells involved in the pathogenesis of many neurodegenerative diseases acquire the features of cytotoxic and phagocytic cells in response to certain pathogens and inflammatory signals. K(ATP) channels are energy sensors of ATP availability that link the cell's metabolic state to its membrane excitability. In pancreatic beta cells, they promote glucose-dependent insulin secretion, and in neurones, hyperpolarization that protects against hypoxic damage. This study analyses activated microglia in an in vivo rat neurodegenerative model based on acute hippocampal glutamate receptor overactivation and in postmortem samples from patients with Alzheimer's disease. We demonstrate that in activated microglia the K(ATP) channel components SUR-1 or SUR-2 are present together with glucokinase. Our results indicate that, according to glucose availability, these channels may modify microglia membrane potential. The functional relevance of these channels is seen as a new mechanism modulating the effects of external signals on microglia.

Comparative immunohistochemical distribution of three small-conductance Ca2+-activated potassium channel subunits, SK1, SK2, and SK3 in mouse brain

To investigate the distribution of all three SK channel subunits in the mouse central nervous system, we performed immunohistochemistry using sequence-specific antibodies directed against SK1, SK2, and SK3 proteins. Expression of SK1 and SK2 proteins revealed a partly overlapping distribution pattern restricted to a limited number of brain areas (e.g., neocortex, hippocampal formation). In contrast, SK3 immunoreactivity was rather complementary and predominantly detected in phylogenetically older brain regions like basal ganglia, thalamus, and various brain stem nuclei (e.g., locus coeruleus, tegmental nuclei). At the cellular level, SK1- and SK2-like immunoreactivity was primarily localized to somatic and dendritic structures, whereas the majority of SK3-like immunoreactivity was associated with varicose fibers.

KCNE2 protein is expressed in ventricles of different species, and changes in its expression contribute to electrical remodeling in diseased hearts

BACKGROUND

Mutations in KCNE2 have been linked to long-QT syndrome (LQT6), yet KCNE2 protein expression in the ventricle and its functional role in native channels are not clear.

METHODS AND RESULTS

We detected KCNE2 protein in human, dog, and rat ventricles in Western blot experiments. Immunocytochemistry confirmed KCNE2 protein expression in ventricular myocytes. To explore the functional role of KCNE2, we studied how its expression was altered in 2 models of cardiac pathology and whether these alterations could help explain observed changes in the function of native channels, for which KCNE2 is a putative auxiliary (beta) subunit. In canine ventricle injured by coronary microembolizations, the rapid delayed rectifier current (I(Kr)) density was increased. Although the protein level of ERG (I(Kr) pore-forming, alpha, subunit) was not altered, the KCNE2 protein level was markedly reduced. These data are consistent with the effect of heterologously expressed KCNE2 on ERG and suggest that in canine ventricle, KCNE2 may associate with ERG and suppress its current amplitude. In aging rat ventricle, the pacemaker current (I(f)) density was increased. There was a significant increase in the KCNE2 protein level, whereas changes in the alpha-subunit (HCN2) were not significant. These data are consistent with the effect of heterologously expressed KCNE2 on HCN2 and suggest that in aging rat ventricle, KCNE2 may associate with HCN2 and enhance its current amplitude.

CONCLUSIONS

KCNE2 protein is expressed in ventricles, and it can play diverse roles in ventricular electrical activity under (patho)physiological conditions.

Spinal circuits formation: a study of developmentally regulated markers in organotypic cultures of embryonic mouse spinal cord

In this study, we have addressed the issue of neural circuit formation using the mouse spinal cord as a model system. Our primary objective was to assess the suitability of organotypic cultures from embryonic mouse spinal cord to investigate, during critical periods of spinal network formation, the role of the local spinal cellular environment in promoting circuit development and refinement. These cultures offer the great advantage over other in vitro systems, of preserving the basic cytoarchitecture and the dorsal-ventral orientation of the spinal segment from which they are derived [Eur J Neurosci 14 (2001) 903; Eur J Neurosci 16 (2002) 2123]. Long-term embryonic spinal cultures were developed and analyzed at sequential times in vitro, namely after 1, 2, and 3 weeks. Spatial and temporal regulation of neuronal and non-neuronal markers was investigated by immunocytochemical and Western blotting analysis using antibodies against: a) the non-phosphorylated epitope of neurofilament H (SMI32 antibody); b) the enzyme choline acetyltransferase, to localize motoneurons and cholinergic interneurons; c) the enzyme glutamic acid decarboxylase 67, to identify GABAergic interneurons; d) human eag-related gene (HERG) K(+) channels, which appear to be involved in early stages of neuronal and muscle development; e) glial fibrillary acidic protein, to identify mature astrocytes; f) myelin basic protein, to identify the onset of myelination by oligodendrocytes. To examine the development of muscle acetylcholine receptors clusters in vitro, we incubated live cultures with tetramethylrhodamine isothiocyanate-labeled alpha-bungarotoxin, and we subsequently immunostained them with SMI32 or with anti-myosin antibodies. Our results indicate that the developmental pattern of expression of these markers in organotypic cultures shows close similarities to the one observed in vivo. Therefore, spinal organotypic cultures provide a useful in vitro model system to study several aspects of neurogenesis, gliogenesis, muscle innervation, and synaptogenesis.

Immunohistochemical localization of the voltage-gated potassium channel subunit Kv1.4 in the central nervous system of the adult rat

A large set of voltage-gated potassium channels is involved in regulating essential aspects of neuronal function in the central nervous system, thus contributing to the ability of neurons to respond to a given input. In the present study, we used immunocytochemical methods to elucidate the regional, cellular and subcellular distribution of the voltage-gated potassium channel subunit Kv1.4, a member of the Shaker subfamily, in the brain. At the light microscopic level, the Kv1.4 subunit showed a unique distribution pattern, being localized in specific neuronal populations of the rat brain. The neuronal regions expressing the highest levels of Kv1.4 protein included the cerebral cortex, the hippocampus, the posterolateral and posteromedial ventral thalamic nuclei, the dorsolateral and medial geniculate nuclei, the substantia nigra and the dorsal cochlear nucleus. The Kv1.4 subunit was also present in other neuronal populations, with different levels of Kv1.4 immunoreactivity. In all immunolabeled regions, the Kv1.4 subunit was mostly diffusely distributed and, to a lesser extent, it stained cell bodies and proximal dendrites. Furthermore, Kv1.4 immunoreactivity was also detected in nerve terminals and axonal terminal fields. At the electron microscopic level, Kv1.4 was located postsynaptically in dendritic spines and shafts at extrasynaptic sites, as well as presynaptically in axon and active zone of axon terminals, in the neocortex and hippocampus. The findings indicate that Kv1.4 channels are widely distributed in the rat brain and suggest that activation of this channel would have different modulatory effects on neuronal excitability.

Co-expression of mCysLT1 receptors and IK channels in Xenopus laevis oocytes elicits LTD4-stimulated IK current, independent of an increase in [Ca2+]i

Addition of LTD4 (10 nM) to Xenopus laevis oocytes expressing the mCysLT1 receptor together with hBK or hIK channels resulted in the activation of both channels secondary to an LTD4-induced increase in [Ca2+]i. In addition, the hIK channel is activated by low concentrations of LTD4 (<0.1 nM), which did not result in any increase in [Ca2+]i. Even though activation of hIK by low concentrations of LTD4 was independent of an increase in [Ca2+]i, a certain "permissive" level of [Ca2+]i was required for its activation, since buffering of intracellular Ca2+ by EGTA completely abolished the response to LTD4. Neither hTBAK1 nor hTASK2 was activated following stimulations with LTD4 (0.1 and 100 nM).

Cochlear immunochemistry--a new technique based on gelatin embedding

Histological processing of the cochlea for immunochemistry is often a compromise between good anatomical resolution and preservation of antigenicity. Techniques able to preserve tissue architecture invariably demand elevated temperatures and harsh chemicals or a combination of both. The likely result is reduced antigenicity, enzyme activity and nucleic acid integrity. We have modified an existing embedding medium for use in the cochlea that operates at physiological temperature and avoids denaturing agents and organic solvents. Tissue antigenicity is maximised and anatomical detail preserved, normally two mutually exclusive goals. The method is attractive because of its simplicity, speed and transparency for easy cochlear orientation. It is also likely to be adaptable for the infiltration of other heterogeneous structures prone to distortion during frozen sectioning.

Heterogeneous expression of TASK-3 and TRAAK in rat paraganglionic cells

In the present study, we investigated the immunohistochemical localization of the two-pore K+ channels, TASK-3 and TRAAK, in paraganglionic cells within the superior cervical ganglion, stellate ganglion, and aortic body in comparison with membrane channels in chief cells of the carotid body. TASK-3 immunoreactivity was observed in the paraganglionic cells in all tissues examined. TRAAK immunoreactivity was observed in the chief cells of the aortic body as well as these of the carotid body, but not in the paraganglionic cells in the sympathetic (superior cervical and stellate) ganglia. Our findings indicate that sympathetic paraganglionic cells and glossopharyngeal/vagal paraganglionic cells were different from each other in the expression patterns of TASK-3 and TRAAK to result in the different chemoreception properties of sympathetic paraganglionic cells from those of chief cells of the aortic and carotid bodies.

Kv1.5 is an important component of repolarizing K+ current in canine atrial myocytes

Although the canine atrium has proven useful in several experimental models of atrial fibrillation and for studying the effects of rapid atrial pacing on atrial electrical remodeling, it may not fully represent the human condition because of reported differences in functional ionic currents and ion channel subunit expression. In this study, we reassessed the molecular components underlying one current, the ultrarapid delayed rectifier current in canine atrium [IKur(d)], by evaluating the mRNA, protein, immunofluorescence, and currents of the candidate channels. Using reverse transcriptase-polymerase chain reaction, we found that Kv1.5 mRNA was expressed in canine atrium whereas message for Kv3.1 was not detected. Western analysis on cytosolic and membrane fractions of canine tissues, using selective antibodies, showed that Kv3.1 was only detectable in the brain preparations, whereas Kv1.5 was expressed at high levels in both atrial and ventricular membrane fractions. Confocal imaging performed on isolated canine atrial myocytes clearly demonstrated the presence of Kv1.5 immunostaining, whereas that of Kv3.1 was equivocal. Voltage- and current-clamp studies showed that 0.5 mmol/L tetraethylammonium had variable effects on sustained K+ currents, whereas a compound with demonstrated selectivity for hKv1.5 versus Kv3.1, hERG or the sodium channel, fully suppressed canine atrial IKur tail currents and depressed sustained outward K+ current. This agent also increased action potential plateau potentials and action potential duration at 20% and 50% repolarization. These results suggest that in canine atria, as in other species including human, Kv1.5 protein is highly expressed and contributes to IKur.

Potassium channels in human umbilical artery cells

OBJECTIVE

To identify K+ channels of smooth muscle of human umbilical artery using the patch-clamp technique and to study their effect on resting tone of umbilical artery rings.

METHODS

Whole-cell and single-channel patch-clamp recordings in enzymatically isolated smooth muscle cells were made. Measurements of developed isometric force were performed on intact tissue.

RESULTS

Delayed rectifier K+ channels (KDR) and large-conductance Ca2+-activated K+ channels (BKCa) contribute to the whole-cell voltage- and time-dependent outward K+ current, as it was specifically inhibited by 5 mM 4-aminopyridine (4-AP; KDR blocker) (92 +/- 4% at 0 mV, n = 7), by 1 mM tetraethylammonium (TEA; BKCa blocker) (71 +/- 4% at +60 mV, n = 4), and by 200 nM iberiotoxin (BKCa blocker) (64 +/- 7% at +60 mV, n = 4). In outside-out patches, BKCa channels had a single-channel conductance of 132 +/- 4 pS (n = 24) in asymmetric K+ conditions and 216 +/- 4 pS (n = 4) in a symmetric K+ gradient. The activity of the BKCa channels was significantly augmented by 1 microM Ca2+ in the inside-out configuration. 4-AP had no effect on resting tone of intact arterial rings. TEA produced contraction of arterial rings whereas phloretin, an activator of BKCa, relaxed them, which means that BKCa channels are functional in intact tissue and are involved in the maintenance of resting tone in this human vessel.

CONCLUSION

The identities of K+ channels in the human umbilical artery were shown using the patch-clamp technique, and the physiologic effect of K+ channels on resting tone was documented.

Expression of the small conductance Ca2+-activated K+ channel, SK3, in the olfactory ensheathing glial cells of rat brain

Olfactory sensory neurons are wrapped by ensheathing glial cells in the olfactory nerve layer (ONL). Neither functional roles nor electrical properties of ensheathing glial cells have been, as yet, fully clarified. Four subunits (SK1-4) of small conductance Ca2+-activated K+ (SK) channels have been cloned. In the present study, immunohistochemical analyses showed that SK3 channels are expressed in ensheathing glial cells in the rat olfactory bulb, in addition to neuronal cells in other regions. Western blotting analysis demonstrated that SK3 was predominantly expressed in the olfactory bulb, thalamus, moderately in the hippocampus and cerebellum and modestly in the cerebral cortex of the rat brain. SK3 immunoreactivity was detected in the ONL of the olfactory bulb, neural cell body and fibers of the substantia nigra and hypothalamus. SK3 immunoreactivity was quite intense in the outer (superficial) part of the ONL. SK3-immunoreactive structures were overlapped with glial fibrillary acidic protein (GFAP), but not with vimentin, markers for glial cells and olfactory sensory axons, respectively. Immunoelectron microscopy showed that SK3 immunoreactivity was localized in thin processes that enfolded fascicles of immunonegative olfactory nerve axons. These results indicate that SK3 is expressed specifically in the olfactory ensheathing glial cells in olfactory regions.

Regulation of HERG potassium channel activation by protein kinase C independent of direct phosphorylation of the channel protein

OBJECTIVE

Patients with HERG-associated long QT syndrome typically develop tachyarrhythmias during physical or emotional stress. Previous studies have revealed that activation of the beta-adrenergic system and consecutive elevation of the intracellular cAMP concentration regulate HERG channels via protein kinase A-mediated phosphorylation of the channel protein and via direct interaction with the cAMP binding site of HERG. In contrast, the influence of the alpha-adrenergic signal transduction cascade on HERG currents as suggested by recent reports is less well understood. The aim of the present study was to elucidate the biochemical pathways of the protein kinase C (PKC)-dependent regulation of HERG currents.

METHODS

HERG channels were heterologously expressed in Xenopus laevis oocytes, and currents were measured using the two-microelectrode voltage clamp technique.

RESULTS

Application of the phorbol ester PMA, an unspecific protein kinase activator, shifted the voltage dependence of HERG activation towards more positive potentials. This effect could be mimicked by activation of conventional PKC isoforms with thymeleatoxin. Coexpression of HERG with the beta-subunits minK or hMiRP1 did not alter the effect of PMA. Specific inhibition of PKC abolished the PMA-induced activation shift, suggesting that PKC is required within the regulatory mechanism. The PMA-induced effect could still be observed when the PKC-dependent phosphorylation sites in HERG were deleted by mutagenesis. Cytoskeletal proteins such as actin filaments or microtubules did not affect the HERG activation shift.

CONCLUSION

In addition to the known effects of PKA and cAMP, HERG channels are also modulated by PKC. The molecular mechanisms of this PKC-dependent process are not completely understood but do not depend on direct PKC-dependent phosphorylation of the channel.

Ceramide inhibits the potassium channel Kv1.3 by the formation of membrane platforms

Previous studies suggested a central role of sphingomyelin- and cholesterol-enriched membrane rafts in the initiation of signaling via many receptors. Here, we investigated the role of membrane rafts for the function of the voltage-gated potassium channel Kv1.3. We demonstrate that Kv1.3 localizes in the cell membrane to pre-existing small, sphingolipid- and cholesterol-enriched membrane rafts. Transformation of these small rafts to large ceramide-enriched membrane platforms was achieved by stimulation of the endogenous acid sphingomyelinase, addition of exogenous sphingomyelinase or treatment of the cells with C(16)-ceramide and resulted in clustering of Kv1.3 within ceramide-enriched membrane platforms and inhibition of the channel's activity. Likewise, disruption of pre-existing small rafts inhibited Kv1.3 activity. This indicates that intact small membrane rafts are required for Kv1.3 activity and an alteration of the lipid environment of rafts inhibits Kv1.3. These data, thus, may suggest a novel concept for the regulation of ion channels by the cell membrane composition.

The incorporation of an ion channel gene mutation associated with the long QT syndrome (Q9E-hMiRP1) in a plasmid vector for site-specific arrhythmia gene therapy: in vitro and in vivo feasibility studies

The present studies investigated the cardiac potassium channel missense mutation, Q9E-hMiRP1, for potential use as a gene therapy construct for cardiac arrhythmias. This gene abnormality is one of a number of mutations that can cause the long QT syndrome (LQTS), a hereditary arrhythmia disorder that is associated with sudden death. However, individuals who carry the Q9E-hMiRP1 variant are predisposed to developing the LQTS only after clarithromycin administration. Because the electrophysiologic mechanism of action of Q9E-hMiRP1 (i.e., diminished potassium currents resulting in delayed myocardial repolarization) is comparable to that of class III antiarrhythmic agents, we examined Q9E-hMiRP1 as a candidate gene therapy construct for site-specific treatment of reentrant atrial cardiac arrhythmias. Our rationale was also based on the hypothetical safety of the atrial use of Q9E-hMiRP1 because LQTS characteristically causes ventricular but not atrial arrhythmias. Furthermore, the possible use of clarithromycin to control the conduction effects of overexpressed Q9E-hMiRP1 pharmacologically was another attractive feature. In our studies we investigated the use of two bicistronic plasmid DNA gene vectors with either hMiRP1 or Q9E-MiRP1 and green fluorescent protein (GFP), plus a C-terminus of the hMiRP1 or of the Q9E-hMiRP1 coding region for the FLAG (MDYKDDDDK) peptide. We generated two stable cell lines using HEK293 and SH-SY5Y (human cell lines), overexpressing the genes of interest, confirmed by real-time reverse transcription-polymerase chain reaction (RT-PCR) and Western blots. The expected plasma membrane localization of each overexpressed transgene was confirmed by immunofluorescent confocal fluorescent microscopy using anti-FLAG antibody. Patchclamp studies demonstrated that cells transfected with Q9E-hMiRP1 plasmid DNA exhibited significantly reduced potassium currents but only with clarithromycin administration. A novel plasmid DNA delivery system was formulated for use in our animal studies of the hMiRP1 vectors, which was composed of DNA-anti-DNA antibody-cationic lipid (DAC) heteroplexes. In vitro and in vivo studies using DAC heteroplexes containing anti-DNA antibodies with nuclear targeting capability demonstrated significantly increased transfection compared to naked DNA, and to DNA-cationic lipid complexes. Pig atrial myocardial injections of DAC heteroplexes demonstrated 16% of regional cardiac myocytes transfected using the Q9E-hMiRP1 plasmid, and 15% of cells with the hMiRP1 vector. It is concluded that the present studies support the view that site-specific gene therapy for atrial arrhythmias is feasible using plasmid vectors for overexpressing ion channel mutations that have electrophysiologic effects comparable to class III antiarrhythmic agents.

HCN channels are expressed differentially in retinal bipolar cells and concentrated at synaptic terminals

Hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels codetermine the integrative behaviour of neurons and shape their response to synaptic stimulation. We used immunohistochemistry and patch-clamp recording to study the composition and distribution of HCN channels in the rat retina. All four HCN channel isoforms (HCN1-4) are expressed differentially in the retina. In particular, different classes of bipolar cells have a different inventory of HCN channels. We found no evidence for the formation of heterooligomeric HCN channels. HCN channels are densely clustered at synaptic terminals of bipolar cells and photoreceptors. This suggests that HCN channels are involved in the control of transmitter release.

Localization of KCNC1 (Kv3.1) potassium channel subunits in the avian auditory nucleus magnocellularis and nucleus laminaris during development

The KCNC1 (previously Kv3.1) potassium channel, a delayed rectifier with a high threshold of activation, is highly expressed in the time coding nuclei of the adult chicken and barn owl auditory brainstem. The proposed role of KCNC1 currents in auditory neurons is to reduce the width of the action potential and enable neurons to transmit high frequency temporal information with little jitter. Because developmental changes in potassium currents are critical for the maturation of the shape of the action potential, we used immunohistochemical methods to examine the developmental expression of KCNC1 subunits in the avian auditory brainstem. The KCNC1 gene gives rise to two splice variants, a longer KCNC1b and a shorter KCNC1a that differ at the carboxy termini. Two antibodies were used: an antibody to the N-terminus that does not distinguish between KCNC1a and b isoforms, denoted as panKCNC1, and another antibody that specifically recognizes the C terminus of KCNC1b. A comparison of the staining patterns observed with the panKCNC1 and the KCNC1b specific antibodies suggests that KCNC1a and KCNC1b splice variants are differentially regulated during development. Although panKCNC1 immunoreactivity is observed from the earliest time examined in the chicken (E10), a subcellular redistribution of the immunoproduct was apparent over the course of development. KCNC1b specific staining has a late onset with immunostaining first appearing in the regions that map high frequencies in nucleus magnocellularis (NM) and nucleus laminaris (NL). The expression of KCNC1b protein begins around E14 in the chicken and after E21 in the barn owl, relatively late during ontogeny and at the time that synaptic connections mature morphologically and functionally.