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R Hendriks

Publications and source records attributed to R Hendriks.

At least 19 recordsLinked to original sources
PubMed1999

Shaw-like potassium currents in the auditory rhombencephalon throughout embryogenesis.

The Shaw subfamily of potassium channel genes, including Kv3.1, are highly expressed within the auditory nuclei of the brainstem, where they have been implicated in the characteristic response properties of particular types of neurons. Potassium currents carried by Kv3.1 are voltage-dependent, have a high activation threshold, are slow to inactivate, and are very sensitive to 4-aminopyridine (4-AP) and tetraethylammonium (TEA). We have investigated the developmental appearance of potassium currents in cell cultures from nucleus magnocellularis and its precursor neuroblasts from the acoustico-vestibular anlage of the chicken. Whole-cell patch recordings revealed that high-threshold, sustained, outward currents were present in 91% of neuroblasts. These currents displayed high sensitivities to TEA and 4-AP. The remaining 9% of neuroblasts exhibited only transient outward currents. Most cells (74%) had both a sustained and an initial transient component of outward current. These current types were observed throughout embryogenesis, beginning with the earliest ages (embryonic day [E]2). During proliferation and migration, and early neuronal differentiation, current levels were low; they incremented gradually during the time when the first synapses occur on dendrites and increased 2- to 3-fold just before hatching, when axosomatic synapses form. These findings suggest that the Shaw subfamily of channels in nucleus magnocellularis may be involved in early neuronal development, as well as in synaptic function later on.

4-Aminopyridine↗
PubMed1999

Role in neuronal cell migration for high-threshold potassium currents in the chicken hindbrain.

We have investigated the influence of voltage-dependent, potassium conductances on the migration of embryonic neurons, using a culture preparation taken from the acoustico-vestibular anlage long before the onset of electrical excitability and synaptic function. Whole-cell patch clamp recordings from migrating neuroblasts at Hamburger-Hamilton stage 28 (E 5.5) revealed the exclusive expression of voltage-dependent, high-threshold, outward currents, activating at potentials positive to -20 mV. These currents were completely suppressed by the potassium channel blockers, 1.0 mM tetraethylammonium chloride (TEA) or 1.0 mM 4-aminopyridine (4-AP). In control media, the active migration of individual neuroblasts was recorded at 27 +/- 6 microm per hr. Within minutes after adding either drug to the culture, normal migration completely stopped for several hours. Calcium channel blockers, omega-conotoxin (3 microM) or cadmium chloride (100 microM), slowed, but did not halt, migration, while nickel chloride (100 microM) or N-methyl-D-glucamine (1 mM) had no effect. However, within 8 hr after TEA exposure, migratory activity usually returned. This recovery was associated with the appearance of a previously undetected, low-threshold and 4-AP- sensitive potassium conductance. We suggest that high-threshold, TEA/4-AP-sensitive potassium channels may normally support the migration of these neurons, while their chronic blockade can be compensated by the appearance of novel potassium channels. Potassium currents may act in concert with N-type calcium channels to regulate neuronal migration.

4-Aminopyridine↗
PubMed1999

Cytosolic ATPases, p97 and NSF, are sufficient to mediate rapid membrane fusion.

Much recent work has focussed on the role of membrane-bound components in fusion. We show here that p97 and NSF are sufficient to mediate rapid membrane fusion. Fractionation of cytosol revealed that p97 and its co-factor, p47, constitutes the major fusion activity. This was confirmed by depleting p97 from the cytosol, which resulted in an 80% decrease in fusion. Using purified protein, p97 or NSF was found to be sufficient to mediate rapid fusion in an ATP-dependent manner. A regulatory role was observed for their corresponding co-factors, p47 and alpha-SNAP. When present at a molar ratio half of that of the ATPase, both co-factors increased fusion activity significantly. Intriguingly, at this ratio the ATPase activity of the complex measured in solution was at its lowest, suggesting that the co-factor stabilizes the ATP state. The fusion event involved mixing of both leaflets of the opposing membranes and contents of liposomes. We conclude from these data that p97, NSF and perhaps other related ATPases catalyse rapid and complete fusion between lipid bilayers on opposing membranes. This highlights a new role for p97 and NSF and prompts a re-evaluation of current fusion models.

Adenosine Triphosphatases↗
PubMed1999

Hippocampal neurochemical and electrophysiological measures from freely moving rats.

This paper describes surgical and recording procedures that have been developed which permit the simultaneous monitoring of levels of select neurochemicals (via microdialysis) and measures of dentate-evoked field potentials within the hippocampal formation of freely moving adult rats. To test and evaluate these procedures, they were employed to examine changes in hippocampal neurochemistry and neuronal excitability associated with the establishment and maintenance of hippocampal long-term potentiation (LTP). Measures of hippocampal norepinephrine (NE) and glutamate levels along with measures of the dentate granule cell population spike amplitude (PSA) were obtained before, during, and after tetanization of the medial perforant path using two separate tetanization paradigms. Results obtained using these new procedures in several animals indicated that changes in NE and glutamate levels were strongly correlated with increases in the dentate granule cell PSA measure obtained following tetanization. The results indicate that this newly developed procedure can be effectively used to directly examine the relationship between neurochemical and neurophysiological changes associated with hippocampal neuroplasticity.

Animals↗
PubMed1995

Screening for mutations causing X-linked severe combined immunodeficiency in the IL-2R gamma chain gene by single-strand conformation polymorphism analysis.

Mutations in the common gamma chain (gamma c or IL2RG) of the interleukin-2, -4, -7, -9 and -15 receptors have been found to cause X-linked severe combined immunodeficiency (SCIDX1). We report here on the mutations identified in a further ten families. Two of the mutations identified have occurred twice in unrelated families, indicating two possible mutational hotspots. Seven of the mutations, which were identified by single-strand conformational polymorphism (SSCP) analysis, are point mutations, and the eighth is a small deletion. We also report on the first use of assays based on these mutations within IL2RG for unambiguous carrier determination. The consequences for the gamma c proteins produced as a result of these mutations are discussed.

Base Sequence↗
PubMed1994

Charybdotoxin and iberiotoxin but not apamin abolish the slow after-hyperpolarization in myenteric plexus neurons.

Myenteric neurons of guinea-pig ileum were studied with intracellular microelectrodes. The specific toxins charybdotoxin, iberiotoxin and apamin were used to characterize the prolonged after-hyperpolarizations of AH neurons in this preparation. Charybdotoxin and iberiotoxin blocked prolonged after-hyperpolarizations in 23 of 24 AH neurons, but apamin had no effect on 5 of 5 AH neurons. Abolition of the after-hyperpolarizations was accompanied by depolarization and increases in input resistances of those AH neurons affected, but the shapes of action potentials were unchanged. The excitability of the AH neurons was enhanced as shown by an increase in the number of action potentials evoked by a 500-ms depolarizing current pulse or by a train of 15-ms depolarizing current pulses (10Hz). The other class of myenteric neurons, S neurons, was also investigated. The 19 S neurons studied fired action potentials only at the start of a 500 ms depolarization, but the toxins had no effect on this behaviour or on their other properties. Intracellular injection of Neurobiotin into the neurons studied and subsequent immunohistochemical staining to localise the calcium-binding protein, calretinin, indicated that all major classes of S neurons were included in the sample. Thus, the prolonged after-hyperpolarizations in AH neurons may be due to opening of a large-conductance (BK) calcium-dependent potassium channel, but similar channels play little or no role in regulation of the excitability of S neurons.

Animals↗
PubMed1993

Evidence for a human IgG1 class switch program.

In activated murine B lymphocytes, immunoglobulin class switch recombination occurs as a highly regulated process which is targeted to distinct switch regions. Here we present first evidence that in human B lymphocytes, switch recombination is targeted to distinct switch regions as well. In a panel of clonally unrelated IgG1-expressing human B cells, immortalized by Epstein-Barr virus (EBV) transformation, seven out of nine cells show switch recombination between S mu and S gamma 1 on both alleles, the active and inactive one. The remaining cells show no switch recombination on the inactive IgH locus. The very strong correlation of switch recombination on both alleles of IgG1-expressing cells proves that class switch recombination to IgG1 is not random but directed in human B lymphocytes.

Alleles↗
PubMed1991

Ramifications of the axons of AH-neurons injected with the intracellular marker biocytin in the myenteric plexus of the guinea pig small intestine.

The projections and terminal ramifications of electrophysiologically characterized myenteric neurons of the guinea pig small intestine were studied after intracellular injection of the marker substance biocytin. Myenteric neurons were impaled with microelectrodes containing 4% biocytin in 2 M KCl (pH 7.4) and characterized electrophysiologically as either AH-neurons or S-neurons. AH-neurons were neurons in which action potentials were followed by prolonged after-hyperpolarizations (lasting greater than 4 seconds). S-neurons were neurons in which such hyperpolarizations were not seen. Electrical stimulation of internodal strands evoked prominent fast excitatory synaptic potentials in S-neurons, but not in AH-neurons. Biocytin was injected electrophoretically into the impaled AH-neurons by passage of hyperpolarizing current (0.6-0.8 nA for 5-15 minutes) through the recording electrode. The preparation was then fixed in Zamboni's fixative, dehydrated, and exposed to avidin coupled to horseradish peroxidase which allowed the injected biocytin to be visualised via a diaminobenzidine reaction. In many cases, the injected biocytin appeared to fill all the processes of injected AH-neurons that ramified within the myenteric plexus. The filled processes included axons running up to 4 mm within the plexus and profuse varicose terminals ramifying within both the ganglion containing the injected cell body and nearby ganglia. Most (90%) cell bodies of the injected AH-neurons had the morphology of Dogiel type II neurons; large, mostly smooth cell bodies with few short processes and several long processes. The other 10% of the AH-neurons had similar cell bodies and long processes but also had prominent short filamentous processes. This population was termed dendritic AH-neurons. The projections and terminals of 28 AH/Dogiel type II neurons and 7 dendritic AH-neurons were analysed in detail. Both types of neurons project circumferentially to provide terminals to nearby ganglia, but the AH/Dogiel type II neurons also provide terminals to their own ganglia while the dendritic AH-neurons typically do not. Although many of the injected AH-neurons had projections orally or anally along the intestine no evidence for a preferential direction of projection was obtained. Analysis of the areas and distributions of the terminal fields of the AH/Dogiel type II neurons suggests that each may contact several other myenteric neurons and that each myenteric neuron may receive input from about ten AH/Dogiel type II neurons.

Action Potentials↗
PubMed1990

Assembly of an in vitro synthesized Escherichia coli outer membrane porin into its stable trimeric configuration.

The folding of in vitro synthesized outer membrane protein PhoE of Escherichia coli was studied in immunoprecipitation experiments with monoclonal antibodies which recognize cell surface-exposed conformational epitopes. The signal sequence appears to interfere with the formation of these conformational epitopes, since a mutant PhoE protein which lacks the majority of the signal peptide could be precipitated four times better than the wild type precursor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the immunoprecipitated PhoE protein revealed that part of the immunoprecipitated PhoE was present as a heat-modifiable form of the protein which migrated faster in the gels than the completely denatured protein. This form of the protein probably represents a folded monomer which might be an intermediate in the assembly of the protein. Outer membrane vesicles were required to induce the formation of small amounts of heat-stable trimers, the functional form of the protein in vivo.

Amino Acid Sequence↗
PubMed1990

An electrophysiological study of the projections of putative sensory neurons within the myenteric plexus of the guinea pig ileum.

Conduction of action potentials in the processes of AH (afterhyperpolarizing) neurons has been examined in the myenteric plexus of the guinea-pig small intestine. AH neurons are a morphologically distinct class of myenteric neurons in which the action potentials are followed by long lasting afterhyperpolarizations and which usually lack fast synaptic inputs. These neurons have large smooth cell bodies and several long processes. We have used electrophysiological methods, combined with intracellular injection of the fluorescent dye 5(6)-carboxyfluorescein, to examine the directions of projection and lengths of axons of AH neurons. AH neurons of the myenteric plexus projected circumferentially in both directions from the cell soma for electrophysiologically determined average distances of 0.74 +/- 0.05 mm. Thus, the neurons span about 1.5 mm of the circumference of the intestine. About one quarter of the AH neurons had one, or rarely two, processes that ran anally after initially projecting circumferentially. All processes conducted action potentials, with average conduction velocities of 0.23 +/- 0.02 ms-1.

Action Potentials↗
PubMed1990

Function of the fully conserved residues Asp99, Tyr52 and Tyr73 in phospholipase A2.

In the active centre of pancreatic phospholipase A2 His48 is at hydrogen-bonding distance to Asp99. This Asp-His couple is assumed to act together with a water molecule as a catalytic triad. Asp99 is also linked via an extended hydrogen bonding system to the side chains of Tyr52 and Tyr73. To probe the function of the fully conserved Asp99, Tyr52 and Tyr73 residues in phospholipase A2, the Asp99 residue was replaced by Asn, and each of the two tyrosines was separately replaced by either a Phe or a Gln. The catalytic and binding properties of the Phe52 and Phe73 mutants did not change significantly relative to the wild-type enzyme. This rules out the possibility that either one of the two Tyr residues in the wild-type enzyme can function as an acyl acceptor or proton donor in catalysis. The Gln73 mutant could not be obtained in any significant amounts probably due to incorrect folding. The Gln52 mutant was isolated in low yield. This mutant showed a large decrease in catalytic activity while its substrate binding was nearly unchanged. The results suggest a structural role rather than a catalytic function of Tyr52 and Tyr73. Substitution of asparagine for aspartate hardly affects the binding constants for both monomeric and micellar substrate analogues. Kinetic characterization revealed that the Asn99 mutant has retained no less than 65% of its enzymatic activity on the monomeric substrate rac 1,2-dihexanoyldithio-propyl-3-phosphocholine, probably due to the fact that during hydrolysis of monomeric substrate by phospholipase A2 proton transfer is not the rate-limiting step.(ABSTRACT TRUNCATED AT 250 WORDS)

Asparagine↗
PubMed1989

Evidence for two types of 5-hydroxytryptamine receptor on secretomotor neurons of the guinea-pig ileum.

Flat sheet preparations of the mucosa plus submucosa from the guinea-pig ileum were placed in Ussing chambers so that short circuit current (Isc), an index of electrolyte movement across the mucosa, could be measured. In these preparations, 5-hydroxytryptamine (5-HT) increases Isc indirectly by stimulating both cholinergic and non-cholinergic secretomotor neurons. The 5-HT3 receptor antagonist, ICS 205-930 (10(-13)-10(-5 M), substantially depressed the secretory response due to 5-HT (10(-6) M), but not that produced by direct activation of muscarinic receptors on the mucosal epithelium with carbachol (10(-6) M), or by stimulation of secretomotor neurons with substance P (10(-8) M) or 1,1-dimethyl-4-phenylpiperazinium (10(-5)M). The residual response to 5-HT, after the addition of a maximally effective concentration of ICS 205-930 (10(-6) M), was further reduced by hyoscine (10(-7) M). When that part of the 5-HT response attributable to the release of acetylcholine was blocked by hyoscine (10(-7) M), ICS 205-930 did not further modify the response to 5-HT. The hyoscine-resistant component was, however, substantially depressed by tetrodotoxin (3.5 x 10(-7) M). The response remaining after ICS 205-930 and hyoscine was not affected by methysergide (2 x 10(-5) M) or cyproheptadine (10(-7) M). We conclude that there are ICS 205-930 sensitive 5-HT receptors on cholinergic secretomotor neurons, and ICS 205-930, methysergide, and cyproheptadine insensitive 5-HT receptors on non-cholinergic secretomotor neurons.

Animals↗
PubMed1988

Plasma protein binding of amiodarone in a patient population: measurement by erythrocyte partitioning and a novel glass-binding method.

1. Amiodarone is an effective antiarrhythmic drug whose therapeutic usefulness is limited by variable pharmacokinetics and considerable toxicity. Total plasma concentrations are not reliably related to therapeutic effect, but if plasma protein binding varies between patients, then free drug concentrations may provide a better measure of drug effectiveness. 2. The plasma protein binding of amiodarone was measured by erythrocyte partitioning, and found to be the same in six healthy subjects and eight patients being treated for cardiac arrhythmias (mean = 99.98%; range 99.97-99.99%). The free fraction of amiodarone was independent of the total drug concentration (r = -0.41, P greater than 0.50) and albumin level (r = -0.31, P greater than 0.50). 3. These data show no advantage in monitoring free concentrations of amiodarone. On the other hand, the patients in this study did not receive very high doses of amiodarone, and were free from drug side effects and biochemical abnormalities. Possibly a more heterogeneous group of patients would show variability in amiodarone binding. This should be examined, especially for patients with variations in alpha 1-acid glycoprotein, a major ligand for basic drugs and a likely major binding protein for amiodarone.

Adult↗
PubMed1988

Pharmacokinetics and tissue distribution of ketanserin in rat, rabbit and dog.

The plasma kinetics and tissue distribution of ketanserin [+)-3-[2-[4-(4-fluorobenzoyl)-1-piperidinyl]ethyl]-2,4(1H,3H)- quinazolinedione, R 41 468) were studied in the rat, rabbit and dog. The studies were performed utilizing 3H- and 14C-labelled ketanserin and appropriate techniques to measure levels of radioactivity, unchanged drug and a major metabolite ketanserin-ol in plasma and tissues. Following intravenous administration to male rats and dogs (10 mg/kg), plasma levels could be described by a two-compartment model. The plasma clearance (C1) averaged 3.8 and 19.2 ml/min/kg and the volume of distribution (Vdss) 0.67 and 4.7 l/kg in male rats and in dogs, respectively. Following oral administration (10-40 mg/kg), ketanserin was rapidly and completely absorbed in all species studied. The absolute bioavailability of oral ketanserin was more than 80% in both rats and dogs. Due to the high clearance of the metabolites in rats, ketanserin was the main component of the plasma radioactivity. In dogs, the fraction of the metabolite ketanserin-ol was more pronounced than that of ketanserin. The apparent elimination half-life of ketanserin was 1.5 h in rabbits, 2-5 h in rats and 3-15 in dogs. The pharmacokinetics of ketanserin were dose-related after single and chronic intravenous and oral dosing. Distribution studies in rats after intravenous and oral administration (10 mg/kg) demonstrated an almost immediate equilibrium between plasma and tissues, resulting in slightly higher tissue than plasma concentrations in the well perfused tissues, and similar or slightly lower levels in the remaining tissues. Ketanserin was the main component of tissue radioactivity. The drug crossed the blood-brain barrier only to a slight extent, brain levels of the unchanged drug being similar to the free fraction in plasma. Ketanserin disappeared from tissues with a similar half-life to that in plasma. On repeated dosing, a small fraction of metabolites was more slowly eliminated. The excretion of the urinary and faecal metabolites after repeated dosing was very similar to that after a single dose. Placental transfer of ketanserin in the rat was limited. On average 0.3% of the maternal radioactive dose, preferentially metabolites, was recovered from the combined foetuses. In dogs orally treated with doses of up to 40 mg/kg/d for 12 months, no undue accumulation or retention of ketanserin or ketanserin-ol was found in any tissue. In lactating dogs orally dosed at 10 mg/kg, preferentially metabolites were excreted in the milk. Concentrations of ketanserin and ketanserin-ol in the milk were respectively 2 and 4 times higher than plasma levels.

Animals↗
PubMed1987

Pharmacokinetics and tissue distribution of the new gastrokinetic agent cisapride in rat, rabbit and dog.

The plasma kinetics and tissue distribution of the gastrokinetic (+/-)-cis-4-amino-5-chloro-N-[1-(3-(4-fluorophenoxy)propyl]-3-methoxy-4- piperidinyl]-2-methoxybenzamide monohydrate (cisapride, R 51 619) have been studied in the rat, rabbit and dog. After intravenous administration to rats (5 mg/kg) and dogs (0.63 mg/kg) plasma level-time curves were adequately fitted to a two-compartmental model. The plasma clearance (ClT) and volume of distribution (Vdss) averaged 91 ml/min.kg and 4.7 l/kg in the rat and 4.2 ml/min.kg and 0.82 l/kg in the dog, respectively. Following oral administration, cisapride was rapidly and almost completely absorbed from the gastrointestinal tract in rats and rabbits. The absorption was somewhat slower in the dog. In male rats the plasma radioactivity was mainly due to metabolites, unaltered cisapride representing on average 10% of the total radioactivity. A markedly larger proportion of the parent drug was seen in female rats. Linear plasma kinetics were observed for cisapride in the dose range of 10 to 160 mg/kg. Similarly in the dog, linearity was observed after oral administration in the range of 0.31 to 10 mg/kg. The plasma kinetics remained unaltered on repeated oral doses of 10 mg/kg to rats and subchronic intravenous administration at 0.63 mg/kg to dogs. Compared with intravenous administration, the absolute bioavailability of oral cisapride was 23% in rats and 53% in the dog for the drug given in solution. The terminal plasma half-life of cisapride was about 1-2 h in the rat and about 4-10 h in the rabbit and dog.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Radioimmunoassay of the new opiate analgesics alfentanil and sufentanil. Preliminary pharmacokinetic profile in man.

The development of two analogous radioimmunoassay (RIA) procedures based on dextran-charcoal separation is described for the quantification of two fentanyl-like analgesics, alfentanil and sufentanil. Immunization of rabbits with conjugates of bovine serum albumin and carboxy-derivatives of the respective drugs resulted in the production of antisera capable of detecting less than 0.05 ng ml-1 of the parent analgesics with high specificity and almost no cross-reactivity with major metabolites. Excellent agreement was obtained between RIA--without prior extraction--and gas chromatography for alfentanil concentrations in human plasma. Because of sufentanil's low therapeutic plasma levels, no comparison could be made between its RIA and an alternative assay, however, there was strong evidence for the specificity of the assay when applied directly to plasma. With these RIA methods preliminary information was obtained on plasma concentrations and elimination of alfentanil or sufentanil in patients given an intravenous bolus injection of 50 micrograms kg-1 of alfentanil, or 5 micrograms kg-1 of sufentanil. For both analgesics, the pharmacokinetic profile in man could be described by a three-compartment model. The terminal elimination half-life was 88 min for alfentanil and 140 min for sufentanil. Six hours after a therapeutic dose, plasma levels were in the order of 3 and 0.3 ng ml-1 for alfentanil and sufentanil respectively.

Alfentanil↗