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Biomedical subjects

B S Jensen

Publications and source records attributed to B S Jensen.

At least 19 recordsLinked to original sources
PubMed2006

Effect of the oral hypoglycaemic sulphonylurea glibenclamide, a blocker of ATP-sensitive potassium channels, on walking distance in patients with intermittent claudication.

AIMS: The oral hypoglycaemic sulphonylurea glibenclamide stimulates endogenous insulin secretion through blockade of ATP-sensitive potassium (KATP) channels on pancreatic beta cells, but also blocks cardiovascular KATP channels, leading to increased peripheral vascular resistance and reduced peripheral blood flow in non-diabetic subjects. Therefore, this study examined whether a single oral dose of glibenclamide adversely affected the pain-free or maximal walking distance in patients with intermittent claudication. METHODS: In a double-blind, randomized crossover study, 12 non-diabetic patients with intermittent claudication were given a single oral dose of glibenclamide (5.25 mg) or placebo separated by a washout period of 1 week. A treadmill test was carried out 180 min after glibenclamide/placebo intake for determination of pain-free and maximal walking distance. Plasma glucose concentrations were kept constant by an euglycemic clamp. Changes in ankle/brachial blood pressure index (ABI), serum insulin, and serum glibenclamide were also assessed. RESULTS: The pain-free walking distance was 62.8 +/- 9.8 metres (mean +/- sem) after glibenclamide and 52.6 +/- 5.9 metres after placebo (P = 0.52). The maximal walking distance was 142.7 +/- 18.7 metres after glibenclamide and 132.6 +/- 16.6 metres after placebo (P = 0.23). The ABI was not significantly changed by glibenclamide compared with placebo. Serum glibenclamide was 0.51 +/- 0.08 microm 180 min after administration of the drug. Glibenclamide produced an 8-fold increase in circulating insulin compared with placebo (P < 0.001). CONCLUSIONS: Glibenclamide given as a single oral dose commonly used in glucose-lowering drug therapy does not reduce pain-free or maximal walking distance in non-diabetic patients with intermittent claudication.

Adenosine Triphosphate↗
PubMed2003

Localization of KCNQ5 in the normal and epileptic human temporal neocortex and hippocampal formation.

The KCNQ family of voltage-dependent non-inactivating K+ channels is composed of five members, four of which (KCNQ2-5) are expressed in the CNS and are responsible for the M-current. Mutations in either KCNQ2 or KCNQ3 lead to a hereditary form of dominant generalized epilepsy. Using specific antisera to the KCNQ2, KCNQ3 and KCNQ5 subunits, we found that KCNQ3 co-immunoprecipitated with KCNQ2 and KCNQ5 subunits, but no association was detected between KCNQ2 and KCNQ5. Intense KCNQ5 immunoreactivity was found to be widely distributed throughout the temporal neocortex and the hippocampal formation. In these structures, both pyramidal and non-pyramidal neurons and a population of glial cells in the white matter expressed the KCNQ5 subunit. In the sclerotic areas of the CA fields of epileptic patients, a marked loss of KCNQ5 immunoreactive pyramidal neurons was found in relation with the loss of neurons in these regions. However, in the regions adjacent to the sclerotic areas, the distribution and intensity of KCNQ5 immunostaining was apparently normal. The widespread distribution of KCNQ5 subunits, its persistence in pharmacoresistant epilepsy, along with the significant role of the M-current in the control of neuronal excitability, makes this protein a possible target for the development of anticonvulsant drugs.

Adolescent↗
PubMed2002

The Ca2+-activated K+ channel of intermediate conductance:a possible target for immune suppression.

The intermediate conductance Ca2+-activated K+ (IK) channel is distinguished from the functionally related Ca2+-activated K+ channels of smaller and larger unitary conductance by its molecular structure, pharmacology, tissue distribution and physiology. Like many K+ channels, IK is an assembly of four identical subunits each spanning the membrane six times and each contributing equally to the K+ selectivity pore positioned centrally in the complex. The IK channel gains its high sensitivity to intracellular Ca2+ from tightly bound calmodulin, and its activity is independent of the membrane potential. Several toxins including charybdotoxin and the more selective mutant, Glu32-charybdotoxin, maurotoxin and stichodactyla toxin potently block IK channels. Among blockers of the IK channel are also several small organic molecules including the antimycotic clotrimazole and the close analogues TRAM-34 and ICA-17043, as well as the antihypertensive, nitrendipine. The IK channel is distributed in peripheral tissues, including secretory epithelia and blood cells, but it appears absent from neuronal and muscle tissue. An important physiological role of the IK channel is to help maintain large electrical gradients for the sustained transport of ions such as Ca2+ influx that controls T lymphocyte (T cell) proliferation. In this review, special attention is given to an analysis of the use of IK blockers as potential immunosuppressants for the treatment of autoimmune disorders such as rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis.

Animals↗
PubMed2001

An ERG channel inhibitor from the scorpion Buthus eupeus.

The isolation of the peptide inhibitor of M-type K(+) current, BeKm-1, from the venom of the Central Asian scorpion Buthus eupeus has been described previously (Fillipov A. K., Kozlov, S. A., Pluzhnikov, K. A., Grishin, E. V., and Brown, D. A. (1996) FEBS Lett. 384, 277-280). Here we report the cloning, expression, and selectivity of BeKm-1. A full-length cDNA of 365 nucleotides encoding the precursor of BeKm-1 was isolated using the rapid amplification of cDNA ends polymerase chain reaction technique from mRNA obtained from scorpion telsons. Sequence analysis of the cDNA revealed that the precursor contains a signal peptide of 21 amino acid residues. The mature toxin consists of 36 amino acid residues. BeKm-1 belongs to the family of scorpion venom potassium channel blockers and represents a new subgroup of these toxins. The recombinant BeKm-1 was produced as a Protein A fusion product in the periplasm of Escherichia coli. After cleavage and high performance liquid chromatography purification, recombinant BeKm-1 displayed the same properties as the native toxin. Three BeKm-1 mutants (R27K, F32K, and R27K/F32K) were generated, purified, and characterized. Recombinant wild-type BeKm-1 and the three mutants partly inhibited the native M-like current in NG108-15 at 100 nm. The effect of the recombinant BeKm-1 on different K(+) channels was also studied. BeKm-1 inhibited hERG1 channels with an IC(50) of 3.3 nm, but had no effect at 100 nm on hEAG, hSK1, rSK2, hIK, hBK, KCNQ1/KCNE1, KCNQ2/KCNQ3, KCNQ4 channels, and minimal effect on rELK1. Thus, BeKm-1 was shown to be a novel specific blocker of hERG1 potassium channels.

Amino Acid Sequence↗
PubMed2001

Apamin interacts with all subtypes of cloned small-conductance Ca2+-activated K+ channels.

The purpose of the present study was to examine how apamin interacts with the three cloned subtypes of small-conductance Ca2+-activated K+ channels (hSK1, rSK2 and rSK3). Expression of the SK channel subtypes in Xenopus laevis oocytes resulted in large outward currents (0.5-5 microA) after direct injection of Ca2+. In all three cases the Ca2+-activated K+ currents could be totally inhibited by 500 nM apamin. Dose-response curves revealed a subtype-specific affinity for the apamin-induced inhibition with IC50 values of 704 pM and 196 nM (biphasic) for hSK1, 27 pM for rSK2 and 4 nM for rSK3. Consistent with these results, membranes prepared from oocytes expressing the SK channel subtypes bound 125I-labelled apamin with distinct dissociation constants (Kd values) of approx. 390 pM for hSK1, 4 pM for rSK2 and 11 pM for rSK3. These results show that apamin binds to and blocks all three subtypes of cloned SK channels, and the distinct values for IC50 and Kd suggest that apamin may be useful for determining the expression pattern of SK channel subtypes in native tissue.

Animals↗
PubMed2001

Pharmacological modulation of SK3 channels.

Small-conductance, calcium-activated K+ channels (SK channels) are voltage-insensitive channels that have been identified molecularly within the last few years. As SK channels play a fundamental role in most excitable cells and participate in afterhyperpolarization (AHP) and spike-frequency adaptation, pharmacological modulation of SK channels may be of significant clinical importance. Here we report the functional expression of SK3 in HEK293 and demonstrate a broad pharmacological profile for these channels. Brain slice studies commonly employ 4-aminopyridine (4-AP) to block voltage-dependent K+ channels or a methyl derivative of bicuculline, a blocker of gamma-aminobutyric acid (GABA)-gated Cl- channels, in order to investigate the role of various synapses in specialized neural networks. However, in this study both 4-AP and bicuculline are shown to inhibit SK3 channels (IC50 values of 512 microM and 6 microM, respectively) at concentrations lower than those used for brain slice recordings. Riluzole, a potent neuroprotective drug with anti-ischemic, anticonvulsant and sedative effects currently used in the treatment of amyotrophic lateral sclerosis, activates SK3 channels at concentrations of 3 microM and above. Amitriptyline, a tricyclic antidepressive widely used clinically, inhibits SK3 channels with an IC50 of 39.1 +/- 10 microM (n=6).

4-Aminopyridine↗
PubMed2001

KCNQ4 channel activation by BMS-204352 and retigabine.

Activation of potassium channels generally reduces cellular excitability, making potassium channel openers potential drug candidates for the treatment of diseases related to hyperexcitabilty such as epilepsy, neuropathic pain, and neurodegeneration. Two compounds, BMS-204352 and retigabine, presently in clinical trials for the treatment of stroke and epilepsy, respectively, have been proposed to exert their protective action via an activation of potassium channels. Here we show that KCNQ4 channels, stably expressed in HEK293 cells, were activated by retigabine and BMS-204352 in a reversible and concentration-dependent manner in the concentration range 0.1-10 microM. Both compounds shifted the KCNQ4 channel activation curves towards more negative potentials by about 10 mV. Further, the maximal current obtainable at large positive voltages was also increased concentration-dependently by both compounds. Finally, a pronounced slowing of the deactivation kinetics was induced in particular by BMS-204352. The M-current blocker linopirdine inhibited the baseline current, as well as the BMS-204352-induced activation of the KCNQ4 channels. KCNQ2, KCNQ2/Q3, and KCNQ3/Q4 channels were activated to a similar degree as KCNQ4 channels by 10 microM of BMS-204352 and retigabine, respectively. The compounds are, thus, likely to be general activators of M-like currents.

Anticonvulsants↗
PubMed2001

KCNQ4 channels expressed in mammalian cells: functional characteristics and pharmacology.

Human cloned KCNQ4 channels were stably expressed in HEK-293 cells and characterized with respect to function and pharmacology. Patch-clamp measurements showed that the KCNQ4 channels conducted slowly activating currents at potentials more positive than -60 mV. From the Boltzmann function fitted to the activation curve, a half-activation potential of -32 mV and an equivalent gating charge of 1.4 elementary charges was determined. The instantaneous current-voltage relationship revealed strong inward rectification. The KCNQ4 channels were blocked in a voltage-independent manner by the memory-enhancing M current blockers XE-991 and linopirdine with IC(50) values of 5.5 and 14 microM, respectively. The antiarrhythmic KCNQ1 channel blocker bepridil inhibited KCNQ4 with an IC(50) value of 9.4 microM, whereas clofilium was without significant effect at 100 microM. The KCNQ4-expressing cells exhibited average resting membrane potentials of -56 mV in contrast to -12 mV recorded in the nontransfected cells. In conclusion, the activation and pharmacology of KCNQ4 channels resemble those of M currents, and it is likely that the function of the KCNQ4 channel is to regulate the subthreshold electrical activity of excitable cells.

Animals↗
PubMed2001

The Ca2+-activated K+ channel of intermediate conductance: a molecular target for novel treatments?

This review discusses the Ca2+-activated K+ channels of intermediate conductance (IK channels), and their historical discovery in erythrocytes, their classical biophysical characteristics, physiological function, molecular biology as well as their role as possible molecular targets for pharmacological intervention in various diseases. The first described Ca2+-activated K+ channel ever - the so-called Gard6s channel from human erythrocytes--is an IK channel. The "I" denominates the intermediate conductance that distinguishes the IK channels from the related Ca2+-activated K+ channels of small (SK) or large (BK) conductance. The recent cloning of the human IK channel gene (KCNN4) enabled a detailed mapping of the expression in various tissues. IK channel expression is found predominantly in cells of the blood, in epithelia and endothelia. An important physiological role of IK channels is to set the membrane potential at fairly negative values and thereby to build up large electrical gradients for the passive transport of ions such as Cl- efflux driving water and Na+ secretion from epithelia, and Ca2+ influx controlling T-lymphocyte proliferation. The molecular cloning of IK and SK channels has revealed that both channels gain their Ca2+-sensitivity from tightly bound calmodulin (CaM). The IK channel is potently blocked by the scorpion toxin charybdotoxin (ChTx) and the antimycotic clotrimazole (CLT). CLT has been in clinical trials for the treatment of sickle cell disease, diarrhea and ameliorates the symptoms of rheumatoid arthritis. However, inhibition of cytochrome P450 enzymes by CLT limits its therapeutic value, but new drug candidates are entering the stage. It is discussed whether pharmacological modulation of IK channels may be beneficial in sickle cell anemia, cystic fibrosis, secretory diarrhea, craft-versus-host disease and autoimmune diseases.

Amino Acid Sequence↗
PubMed2000

Inhibition of the human intermediate-conductance, Ca2+-activated K+ channel by intracellular acidification.

The effect of changes in pH on the gating properties of the cloned human intermediate-conductance, Ca2+-activated K+ channel (hIK) was studied using the patch-clamp technique. Multi-channel inside-out recordings of patches from HEK-293 cells stably expressing hIK channels revealed that the channel activity is modulated by changes in intracellular pH (pHi). Changes in extracellular pH (pHo) in the range from pH 6.0 to 8.2 did not affect the hIK whole-cell current. Intracellular acidification gradually decreased the activity of the hIK channel, approaching zero activity at pHi 6.0. Decreasing pHi altered neither the conductance nor the inward rectification of hIK channels. The proton-induced inhibition of the multi-channel hIK patch current could not be counteracted by increasing the cytosolic Ca2+ concentration to 30 microM. The molecular sensory mechanism underlying the proton-induced modulation of hIK gating is at present unknown.

Acid-Base Imbalance↗
PubMed2000

Activation of the human, intermediate-conductance, Ca2+-activated K+ channel by methylxanthines.

This study demonstrated that the methylxanthines, theophylline, IBMX and caffeine, activate the human, intermediate-conductance, Ca2+-activated K+ channel (hIK) stably expressed in HEK-293 cells. Whole-cell voltage-clamp experiments showed that the hIK current increased reversibly and voltage independently after the addition of methylxanthines. In current-clamp experiments, theophylline dose-dependently hyperpolarised the cell membrane from a resting potential of -18 mV to -56 mV. The methylxanthines did not affect large-conductance (BK) or small-conductance (SK2), Ca2+-activated K+ channels, demonstrating that the effects were not secondary to a rise in intracellular Ca2+. However, the activation of hIK by theophylline required an intracellular [Ca2+] above 30 nM. The hIK current was insensitive to 8-bromoadenosine cyclic 3',5'-monophosphate (8-bromo-cAMP), forskolin, 8-bromoguanosine cyclic 3',5'-monophosphate (8-bromo-cGMP) and sodium nitroprusside. Moreover, in the presence of inhibitors of protein kinase A (PKA) or protein kinase G (PKG) theophylline still activated the current. Finally, mutation of the putative PKA/PKG consensus phosphorylation site (Ser334) had no effect on the theophylline-induced activation of hIK. Since the observed activation is independent of changes in PKA/PKG-phosphorylation and of fluctuations in intracellular Ca2+, we suggest that the methylxanthines interact directly with the hIK protein.

1-Methyl-3-isobutylxanthine↗
PubMed1999

Inhibition of T cell proliferation by selective block of Ca(2+)-activated K(+) channels.

T lymphocytes express a plethora of distinct ion channels that participate in the control of calcium homeostasis and signal transduction. Potassium channels play a critical role in the modulation of T cell calcium signaling, and the significance of the voltage-dependent K channel, Kv1.3, is well established. The recent cloning of the Ca(2+)-activated, intermediate-conductance K(+) channel (IK channel) has enabled a detailed investigation of the role of this highly Ca(2+)-sensitive K(+) channel in the calcium signaling and subsequent regulation of T cell proliferation. The role IK channels play in T cell activation and proliferation has been investigated by using various blockers of IK channels. The Ca(2+)-activated K(+) current in human T cells is shown by the whole-cell voltage-clamp technique to be highly sensitive to clotrimazole, charybdotoxin, and nitrendipine, but not to ketoconazole. Clotrimazole, nitrendipine, and charybdotoxin block T cell activation induced by signals that elicit a rise in intracellular Ca(2+)-e.g., phytohemagglutinin, Con A, and antigens such as Candida albicans and tetanus toxin in a dose-dependent manner. The release of IFN-gamma from activated T cells is also inhibited after block of IK channels by clotrimazole. Clotrimazole and cyclosporin A act synergistically to inhibit T cell proliferation, which confirms that block of IK channels affects the process downstream from T cell receptor activation. We suggest that IK channels constitute another target for immune suppression.

Calcium↗
PubMed1999

[Working environment in Danish veterinary clinics].

Occupational health risks to veterinary personnel have been recognized in other countries. We have investigated the situation in Denmark by use of a questionnaire sent to 654 veterinarians identified through telephone books. Seventy-one percent responded. Two-thirds used inhalational anaesthesia; one-half had noticed the smell of gas, mostly one to four times per week, others even more frequently. Room ventilation existed in 85% of the clinics, local exhaust in 68% of those using anaesthetic gases. Eighty-one percent worked with X-rays, almost all using lead aprons, 83% lead gloves; two-thirds always carried film badges, the rest only occasionally; 4.4% had shown exposure within the last five years. One half applied insecticides two-thirds frequently other powders, creams or ointments. Almost everybody applied antibiotics, one-fourth local analgesics. Eighty-eight percent wore gloves in various contexts, though only 5% wore gloves consistently on animal contact. In conclusion, occupational hazards are identified, with obvious possibilities for improvements at reasonable costs.

Adult↗
PubMed1998

Functional characterization of mongoose nicotinic acetylcholine receptor alpha-subunit: resistance to alpha-bungarotoxin and high sensitivity to acetylcholine.

The mongoose is resistant to snake neurotoxins. The mongoose muscle nicotinic acetylcholine receptor (AChR) alpha-subunit contains a number of mutations in the ligand-binding domain and exhibits poor binding of alpha-bungarotoxin (alpha-BTX). We characterized the functional properties of a hybrid (alpha-mongoose/beta gamma delta-rat) AChR. Hybrid AChRs, expressed in Xenopus oocytes, respond to acetylcholine with depolarizing current, the mean maximal amplitude of which was greater than that mediated by the rat AChR. The IC50 of alpha-BTX to the hybrid AChR was 200-fold greater than that of the rat, suggesting much lower affinity for the toxin. Hybrid AChRs exhibited an apparent higher rate of desensitization and higher affinity for ACh (EC50 1.3 vs. 23.3 microM for the rat AChR). Hence, changes in the ligand-binding domain of AChR not only affect the binding properties of the receptor, but also result in marked changes in the characteristics of the current.

Acetylcholine↗
PubMed1998

The mongoose acetylcholine receptor alpha-subunit: analysis of glycosylation and alpha-bungarotoxin binding.

The mongoose AChR alpha-subunit has been cloned and shown to be highly homologous to other AChR alpha-subunits, with only six differences in amino acid residues at positions that are conserved in animal species that bind alpha-bungarotoxin (alpha-BTX). Four of these six substitutions cluster in the ligand binding site, and one of them, Asn-187, forms a consensus N-glycosylation site. The mongoose glycosylated alpha-subunit has a higher apparent molecular mass than that of the rat glycosylated alpha-subunit, probably resulting from the additional glycosylation at Asn-187 of the mongoose subunit. The in vitro translated mongoose alpha-subunit, in a glycosylated or non-glycosylated form, does not bind alpha-BTX, indicating that lack of alpha-BTX binding can be achieved also in the absence of glycosylation.

Amino Acid Sequence↗
PubMed1998

Long-term outcome of spinal cord electrical stimulation in patients with refractory chest pain.

BACKGROUND AND HYPOTHESIS: Treatment of patients with refractory chest pain remains a challenge. In this study, the long-term clinical effects of spinal cord electrical stimulation were evaluated in 10 consecutive male patients (mean age 53.7 years) with chronic chest pain in a prospective observational study. METHODS: After placement of the electrode in an epidural position and before implantation of the device, patients were subjected to clinical evaluation, including atrial pacing, in order to document significant antianginal effects. RESULTS: Spinal cord electrical stimulation abolished or improved pacing time to angina by more than 50% in seven of the patients who subsequently had the device implanted. In three of these patients, the system was ineffective after a period of 3-9 months despite paresthesia in the area of anginal pain with electrical stimulation. The effects of treatment remained satisfactory in the remaining patients (40%) after a mean follow-up of 60 (45-72) months. Thus, a long-lasting clinical response was able to be predicted in 57% of the patients. CONCLUSION: Spinal cord electrical stimulation is one of the few therapeutic options in inoperable patients with refractory chest pain.

Aged↗