Passive immunotherapy with a novel antibody against 3pE-modified Aβ demonstrates potential for enhanced efficacy and favorable safety in combination with BACE inhibitor treatment in plaque-depositing mice

The imbalance between production and clearance of amyloid β (Aβ) peptides and their resulting accumulation in the brain is an early and crucial step in the pathogenesis of Alzheimer's disease (AD). Therefore, Aβ is strongly positioned as a promising and extensively validated therapeutic target for AD. Investigational disease-modifying approaches aiming at reducing cerebral Aβ concentrations include prevention of de novo production of Aβ through inhibition of β-site amyloid precursor protein cleaving enzyme 1 (BACE1), and clearance of Aβ deposits via passive Aβ immunotherapy. We have developed a novel, high affinity antibody against Aβ peptides bearing a pyroglutamate residue at amino acid position 3 (3pE), an Aβ species abundantly present in plaque deposits in AD brains. Here, we describe the preclinical characterization of this antibody, and demonstrate a significant reduction in amyloid burden in the absence of microhemorrhages in different mouse models with established plaque deposition. Moreover, we combined antibody treatment with chronic BACE1 inhibitor treatment and demonstrate significant clearance of pre-existing amyloid deposits in transgenic mouse brain, without induction of microhemorrhages and other histopathological findings. Together, these data confirm significant potential for the 3pE-specific antibody to be developed as a passive immunotherapy approach that balances efficacy and safety. Moreover, our studies suggest further enhanced treatment efficacy and favorable safety after combination of the 3pE-specific antibody with BACE1 inhibitor treatment.

Anti-Tau Monoclonal Antibodies Derived from Soluble and Filamentous Tau Show Diverse Functional Properties in vitro and in vivo

The tau spreading hypothesis provides rationale for passive immunization with an anti-tau monoclonal antibody to block seeding by extracellular tau aggregates as a disease-modifying strategy for the treatment of Alzheimer's disease (AD) and potentially other tauopathies. As the biochemical and biophysical properties of the tau species responsible for the spatio-temporal sequences of seeding events are poorly defined, it is not yet clear which epitope is preferred for obtaining optimal therapeutic efficacy. Our internal tau antibody collection has been generated by immunizations with different tau species: aggregated- and non-aggregated tau and human postmortem AD brain-derived tau fibrils. In this communication, we describe and characterize a set of these anti-tau antibodies for their biochemical and biophysical properties, including binding, tissue staining by immunohistochemistry, and epitope. The antibodies bound to different domains of the tau protein and some were demonstrated to be isoform-selective (PT18 and hTau56) or phospho-selective (PT84). Evaluation of the antibodies in cellular- and in vivo seeding assays revealed clear differences in maximal efficacy. Limited proteolysis experiments support the hypothesis that some epitopes are more exposed than others in the tau seeds. Moreover, antibody efficacy seems to depend on the structural properties of fibrils purified from tau Tg mice- and postmortem human AD brain.

Selective inhibition of intestinal guanosine 3',5'-cyclic monophosphate signaling by small-molecule protein kinase inhibitors

The guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase II (cGKII) serine/threonine kinase relays signaling through guanylyl cyclase C (GCC) to control intestinal fluid homeostasis. Here, we report the discovery of small-molecule inhibitors of cGKII. These inhibitors were imidazole-aminopyrimidines, which blocked recombinant human cGKII at submicromolar concentrations but exhibited comparatively little activity toward the phylogenetically related protein kinases cGKI and cAMP-dependent protein kinase (PKA). Whereas aminopyrimidyl motifs are common in protein kinase inhibitors, molecular modeling of these imidazole-aminopyrimidines in the ATP-binding pocket of cGKII indicated an unconventional binding mode that directs their amine substituent into a narrow pocket delineated by hydrophobic residues of the hinge and the αC-helix. Crucially, this set of residues included the Leu-530 gatekeeper, which is not conserved in cGKI and PKA. In intestinal organoids, these compounds blocked cGKII-dependent phosphorylation of the vasodilator-stimulated phosphoprotein (VASP). In mouse small intestinal tissue, cGKII inhibition significantly attenuated the anion secretory response provoked by the GCC-activating bacterial heat-stable toxin (STa), a frequent cause of infectious secretory diarrhea. In contrast, both PKA-dependent VASP phosphorylation and intestinal anion secretion were unaffected by treatment with these compounds, whereas experiments with T84 cells indicated that they weakly inhibit the activity of cAMP-hydrolyzing phosphodiesterases. As these protein kinase inhibitors are the first to display selective inhibition of cGKII, they may expedite research on cGMP signaling and may aid future development of therapeutics for managing diarrheal disease and other pathogenic syndromes that involve cGKII.

GLMM approach to study the spatial and temporal evolution of spikes in the small intestine

Mixed models can be applied in a wide range of settings. Probably, they are most commonly used to handle grouping in the data. In addition, mixed models can be used for smoothing purposes as well. When dealing with non-normal data, the use of smoothing methods within the generalized linear mixed models (GLMM) framework is less familiar. We explore the use of GLMM for smoothing purposes in both spatial and longitudinal dimensions. The methodology is illustrated by analysis of spike potentials in the small intestine of different cats. Spatio-temporal models that use two-dimensional smoothing splines across the spatial dimension and random effects to account for the correlations during successive slow-waves are developed. A major advantage of the mixed-model approach is that it can handle smoothing together with grouping (or other types of correlations) in a unified model. In this way, areas with high spike incidence compared with other areas can be detected. Also, the temporal and spatial characteristics of spikes during successive slow-waves can be identified.

Inhibition of Heat-Stable Toxin-Induced Intestinal Salt and Water Secretion by a Novel Class of Guanylyl Cyclase C Inhibitors

BACKGROUND

Many enterotoxigenic Escherichia coli strains produce the heat-stable toxin, STa, which, by activation of the intestinal receptor-enzyme guanylyl cyclase (GC) C, triggers an acute, watery diarrhea. We set out to identify GCC inhibitors that may be of benefit for the treatment of infectious diarrheal disease.

METHODS

Compounds that inhibit STa-induced cyclic guanosine 3',5'-monophosphate (cGMP) production were selected by performing cyclase assays on cells and membranes containing GCC, or the related GCA. The effect of leads on STa/GCC-dependent activation of the cystic fibrosis transmembrane conductance regulator anion channel was investigated in T84 cells, and in porcine and human intestinal tissue. Their effect on STa-provoked fluid transport was assessed in ligated intestinal loops in piglets.

RESULTS

Four N-2-(propylamino)-6-phenylpyrimidin-4-one-substituted piperidines were shown to inhibit GCC-mediated cellular cGMP production. The half maximal inhibitory concentrations were ≤ 5 × 10(-7) mol/L, whereas they were >10 times higher for GCA. In T84 monolayers, these leads blocked STa/GCC-dependent, but not forskolin/adenylyl cyclase-dependent, cystic fibrosis transmembrane conductance regulator activity. GCC inhibition reduced STa-provoked anion secretion in pig jejunal tissue, and fluid retention and cGMP levels in STa-exposed loops. These GCC inhibitors blocked STa-provoked anion secretion in rectal biopsy specimens.

CONCLUSIONS

We have identified a novel class of GCC inhibitors that may form the basis for development of future therapeutics for (infectious) diarrheal disease.

Preclinical evaluation of the antipsychotic potential of the mGlu2-positive allosteric modulator JNJ-40411813

JNJ-40411813/ADX71149 (1-butyl-3-chloro-4-(4-phenylpiperidin-1-yl) pyridin-2(1H)-one) is a positive allosteric modulator (PAM) of the mGlu2 receptor, which also displays 5-Hydroxytryptamine (5HT2A) antagonism after administration in rodents due to a rodent-specific metabolite. JNJ-40411813 was compared with the orthosteric mGlu2/3 agonist LY404039 (4-amino-2-thiabicyclo [3.1.0] hexane-4,6-dicarboxylic acid 2,2-dioxide), the selective mGlu2 PAM JNJ-42153605 (3-(cyclopropylmethyl)-7-(4-phenylpiperidin-1-yl)-8-(trifluoromethyl)[1,2,4]triazolo[4,3-a]pyridine) and the 5HT2A antagonist ritanserin in rodent models for antipsychotic activity and potential side effects, attempting to differentiate between the various compounds and mechanisms of action. In mice, JNJ-40411813, JNJ-42153605, and LY404039 inhibited spontaneous locomotion and phencyclidine- and scopolamine-induced but not d-amphetamine-induced hyperlocomotion; the 5HT2A antagonist ritanserin inhibited only spontaneous locomotion and phencyclidine-induced hyperlocomotion. As measured by 2-deoxyglucose uptake, all compounds reversed memantine-induced brain activation in mice. The two mGlu2 PAMs and LY404039, but not ritanserin, inhibited conditioned avoidance behavior in rats. Like ritanserin, the mGlu2 ligands antagonized 2,5-dimethoxy-4-methylamphetamine-induced head twitches in rats. LY404039 but not the mGlu2 PAMs impaired rotarod performance in rats and increased the acoustic startle response in mice. Our results show that although 5HT2A antagonism has effect in some models, mGlu2 receptor activation is sufficient for activity in several animal models of antipsychotic activity. The mGlu2 PAMs mimicked the in vivo pharmacodynamic effects observed with LY404039 except for effects on the rotarod and acoustic startle, suggesting that they produce a primary activity profile similar to that of the mGlu2/3 receptor agonist while they can be differentiated based on their secondary activity profile. The results are discussed in light of clinical data available for some of these molecules, in particular JNJ-40411813.

Effect of stress and peripheral immune activation on astrocyte activation in transgenic bioluminescent Gfap-luc mice

Neuroinflammation and the accompanying activation of glial cells is an important feature of many neurodegenerative conditions. It is known that factors such as peripheral infections and stress can influence immune processes in the brain. However, the effect of these stressors on astrocyte activation in vivo remains elusive. In this study, transgenic Gfap-luc mice expressing the luciferase gene under the transcriptional control of the glial fibrillary acidic protein promoter were used to quantify the kinetics of in vivo astrocyte activation following immune challenges relevant to clinical inflammation. It was found that astrocytes respond rapidly to peripheral immune activation elicited by either bacterial lipopolysaccharide (LPS) or the viral mimetic polyinosinic:polycytidylic acid (poly(I:C)). By measuring bioluminescence and 18-kDa translocator protein radioligand binding in the same animal it was observed that LPS induces both astrocyte as well as microglial activation at 6 h post-administration. Furthermore, the astrocyte response decreased upon repeated systemic LPS injections, indicating development of tolerance to the LPS challenge. Finally, restraining Gfap-luc mice for 1 h daily on 5 consecutive days did not affect brain bioluminescence, thereby indicating that sub-chronic stress does not influence astrocyte activation under unchallenged conditions. However, stressed animals showed a reduced response to a subsequent systemic LPS injection, suggesting that the immune system is compromised in these animals. Here, we demonstrate that Gfap-luc mice can be used to study astrocyte activation in response to stimuli relevant for clinical inflammation and that this approach may provide a more complete characterization of existing and novel models of neuroinflammation

Intracerebral injection of preformed synthetic tau fibrils initiates widespread tauopathy and neuronal loss in the brains of tau transgenic mice

Neurofibrillary tangles composed of hyperphosphorylated fibrillized tau are found in numerous tauopathies including Alzheimer's disease. Increasing evidence suggests that tau pathology can be transmitted from cell-to-cell; however the mechanisms involved in the initiation of tau fibrillization and spreading of disease linked to progression of tau pathology are poorly understood. We show here that intracerebral injections of preformed synthetic tau fibrils into the hippocampus or frontal cortex of young tau transgenic mice expressing mutant human P301L tau induces tau hyperphosphorylation and aggregation around the site of injection, as well as a time-dependent propagation of tau pathology to interconnected brain areas distant from the injection site. Furthermore, we show that the tau pathology as a consequence of injection of tau preformed fibrils into the hippocampus induces selective loss of CA1 neurons. Together, our data confirm previous studies on the seeded induction and the spreading of tau pathology in a different tau transgenic mouse model and reveals neuronal loss associated with seeded tau pathology in tau transgenic mouse brain. These results further validate the utility of the tau seeding model in studying disease transmission, and provide a more complete in vivo tauopathy model with associated neurodegeneration which can be used to investigate the mechanisms involved in tau aggregation and spreading, as well as aid in the search for disease modifying treatments for Alzheimer's disease and related tauopathies.

Inactivation of the constitutively active ghrelin receptor attenuates limbic seizure activity in rodents

Ghrelin is a pleiotropic neuropeptide that has been recently implicated in epilepsy. Animal studies performed to date indicate that ghrelin has anticonvulsant properties; however, its mechanism of anticonvulsant action is unknown. Here we show that the anticonvulsant effects of ghrelin are mediated via the growth hormone secretagogue receptor (GHSR). To our surprise, however, we found that the GHSR knockout mice had a higher seizure threshold than their wild-type littermates when treated with pilocarpine. Using both in vivo and in vitro models, we further discovered that inverse agonism and desensitization/internalization of the GHSR attenuate limbic seizures in rats and epileptiform activity in hippocampal slices. This constitutes a novel mechanism of anticonvulsant action, whereby an endogenous agonist reduces the activity of a constitutively active receptor.

Origin and propagation of the slow wave in the canine stomach: the outlines of a gastric conduction system

Slow waves are known to originate orally in the stomach and to propagate toward the antrum, but the exact location of the pacemaker and the precise pattern of propagation have not yet been studied. Using assemblies of 240 extracellular electrodes, simultaneous recordings of electrical activity were made on the fundus, corpus, and antrum in open abdominal anesthetized dogs. The signals were analyzed off-line, pathways of slow wave propagation were reconstructed, and slow wave velocities and amplitudes were measured. The gastric pacemaker is located in the upper part of the fundus, along the greater curvature. Extracellularly recorded slow waves in the pacemaker area exhibited large amplitudes (1.8 +/- 1.0 mV) and rapid velocities (1.5 +/- 0.9 cm/s), whereas propagation in the remainder of the fundus and in the corpus was slow (0.5 +/- 0.2 cm/s) with low-amplitude waveforms (0.8 +/- 0.5 mV). In the antrum, slow wave propagation was fast (1.5 +/- 0.6 cm/s) with large amplitude deflections (2.0 +/- 1.3 mV). Two areas were identified where slow waves did not propagate, the first in the oral medial fundus and the second distal in the antrum. Finally, recordings from the entire ventral surface revealed the presence of three to five simultaneously propagating slow waves. High resolution mapping of the origin and propagation of the slow wave in the canine stomach revealed areas of high amplitude and rapid velocity, areas with fractionated low amplitude and low velocity, and areas with no propagation; all these components together constitute the elements of a gastric conduction system.

Focal activities and re-entrant propagations as mechanisms of gastric tachyarrhythmias

BACKGROUND & AIMS

Gastric arrhythmias occur in humans and experimental animals either spontaneously or induced by drugs or diseases. However, there is no information regarding the origin or the propagation patterns of the slow waves that underlie such arrhythmias.

METHODS

To elucidate this, simultaneous recordings were made on the antrum and the distal corpus during tachygastrias in open abdominal anesthetized dogs using a 240 extracellular electrode assembly. After the recordings, the signals were analyzed, and the origin and path of slow wave propagations were reconstructed.

RESULTS

Several types of arrhythmias could be distinguished, including (1) premature slow waves (25% of the arrhythmias), (2) single aberrant slow waves (4%), (3) bursts (18%), (4) regular tachygastria (11%), and (5) irregular tachygastria (10%). During regular tachygastria, rapid, regular slow waves emerged from the distal antrum or the greater curvature, whereas, during irregular tachygastria, numerous variations occurred in the direction of propagation, conduction blocks, focal activity, and re-entry. In 12 cases, the arrhythmia was initiated in the recorded area. In each case, after a normal propagating slow wave, a local premature slow wave occurred in the antrum. These premature slow waves propagated in various directions, often describing a single or a double loop that re-entered several times, thereby initiating additional slow waves.

CONCLUSIONS

Gastric arrhythmias resemble those in the heart and share many common features such as focal origin, re-entry, circular propagation, conduction blocks, and fibrillation-like behavior.

Role of ghrelin in the relationship between hyperphagia and accelerated gastric emptying in diabetic mice

BACKGROUND & AIMS

Ghrelin is an orexigenic peptide with gastroprokinetic effects. Mice with streptozotocin (STZ)-induced diabetes exhibit hyperphagia, altered gastric emptying, and increased plasma ghrelin levels. We investigated the causative role of ghrelin herein by comparing changes in ghrelin receptor knockout (growth hormone secretagogue receptor [GHS-R](-/-)) and wild-type (GHS-R(+/+)) mice with STZ-induced diabetes.

METHODS

Gastric emptying was measured with the [(13)C]octanoic acid breath test. The messenger RNA (mRNA) expression of neuropeptide Y (NPY), agouti-related peptide (AgRP), and proopiomelanocortin was quantified by real-time reverse-transcription polymerase chain reaction. Neural contractions were elicited by electrical field stimulation in fundic smooth muscle strips.

RESULTS

Diabetes increased plasma ghrelin levels to a similar extent in both genotypes. Hyperphagia was more pronounced in GHS-R(+/+) than in GHS-R(-/-) mice between days 12 and 21. Increases in NPY and AgRP mRNA expression were less pronounced in diabetic GHS-R(-/-) than in GHS-R(+/+) mice from day 15 on, whereas decreases in proopiomelanocortin mRNA levels were similar in both genotypes. Gastric emptying was accelerated to a similar extent in both genotypes, starting on day 16. In fundic smooth muscle strips of diabetic GHS-R(+/+) and GHS-R(-/-) mice, neuronal relaxations were reduced, whereas contractions were increased; this increase was related to an increased affinity of muscarinic and tachykinergic receptors.

CONCLUSIONS

Diabetic hyperphagia is regulated by central mechanisms in which the ghrelin-signaling pathway affects the expression of NPY and AgRP in the hypothalamus. The acceleration of gastric emptying, which is not affected by ghrelin signaling, is not the cause of diabetic hyperphagia and probably involves local contractility changes in the fundus.

Obestatin induction of early-response gene expression in gastrointestinal and adipose tissues and the mediatory role of G protein-coupled receptor, GPR39

Obestatin was identified as a brain/gut peptide hormone encoded by the ghrelin gene and found to interact with the G protein-coupled receptor, GPR39. We investigated target cells for obestatin based on induction of an early-response gene c-fos in different tissues. After ip injection of obestatin, c-fos staining was found in the nuclei of gastric mucosa, intestinal villi, white adipose tissues, hepatic cords, and kidney tubules. Immunohistochemical analyses using GPR39 antibodies further revealed cytoplasmic staining in these tissues. In cultured 3T3-L1 cells, treatment with obestatin, but not motilin, induced c-fos expression. In these preadipocytes, treatment with obestatin also stimulated ERK1/2 phosphorylation. Because phenotypes of GPR39 null mice are partially consistent with a role of GPR39 in mediating obestatin actions, we hypothesized that inconsistencies on the binding of iodinated obestatin to GPR39 are due to variations in the bioactivity of iodinated obestatin. We obtained monoiodoobestatin after HPLC purification and demonstrated its binding to jejunum, stomach, ileum, pituitary, and white adipose tissue. Furthermore, human embryonic kidney 293T cells transfected with plasmids encoding human or mouse GPR39 or a human GPR39 isoform, but not the ghrelin receptor, exhibited high-affinity binding to monoiodoobestatin. Binding studies using jejunum homogenates and recombinant GPR39 revealed obestatin-specific displacement curves. Furthermore, treatment with obestatin induced c-fos expression in gastric mucosa of wild-type, but not GPR39 null, mice, underscoring a mediating role of this receptor in obestatin actions. The present findings indicate that obestatin is a metabolic hormone capable of binding to GPR39 to regulate the functions of diverse gastrointestinal and adipose tissues.

Altered gastrointestinal and metabolic function in the GPR39-obestatin receptor-knockout mouse

BACKGROUND & AIMS

The G-protein-coupled receptor GPR39 is a member of a family that includes the receptors for ghrelin and motilin. Recently the peptide obestatin was identified as a natural ligand for GPR39. The objective of this study was to gain insight into the biological function of the GPR39 receptor.

METHODS

GPR39(-/-) mice were generated and analyzed.

RESULTS

Endogenous GPR39 expression was detected in the brain (septum-amygdala) and the gastrointestinal system (parietal cells, enterocytes, neurons, and pancreas). Gastric emptying of a solid meal (measured by the (14)C octanoic breath test) in GPR39(-/-) mice was accelerated significantly with a gastric half-emptying time of 49.5 +/- 2.2 minutes compared with 86.9 +/- 8.4 minutes in GPR39(+/+) mice. A more effective expulsion of distally located pellets (30%-75% of length) was observed in the colon of GPR39(-/-) mice. Four hours after pylorus ligation, the volume of gastric secretion was increased significantly (GPR39(-/-): 638 +/- 336 microL; GPR39(+/+): 225 +/- 170 microL), but gastric acid secretion was unchanged. The mature body weight and body fat composition of GPR39(-/-) mice was significantly higher compared with GPR39(+/+) mice, but this was not related to hyperphagia because 24-hour food intake did not differ between both genotypes. In contrast, deficiency of the GPR39 receptor led to reduced hyperphagia after fasting. The cholesterol levels were increased significantly in the GPR39(-/-) mice.

CONCLUSIONS

Our data partially confirm and extend the described in vivo effects of obestatin and suggest that this peptide plays a functional role in the regulation of gastrointestinal and metabolic function through interaction with the GPR39 receptor.

Subtractive hybridization unravels a role for the ion cotransporter NKCC1 in the murine intestinal pacemaker

In the small intestine, interstitial cells of Cajal (ICC) surrounding the myenteric plexus generate the pacemaking slow waves that are essential for an efficient intestinal transit. The underlying molecular mechanisms of the slow wave are poorly known. Our aim was to identify ICC-specific genes and their function in the mouse jejunum. Suppression subtractive hybridization using two independent ICC-deficient mouse models identified 56 genes putatively downregulated in the muscularis propria compared with wild-type littermates. Differential expression was confirmed by real-time quantitative PCR for the tyrosine kinase receptor KIT, the established marker for ICC, and for the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). Immunoreactivity for NKCC1 was detected in myenteric ICC but not in the ICC population located at the deep muscular plexus. NKCC1 was also expressed in enteric neurons and mucosal crypts. Bumetanide, an NKCC1 inhibitor, reversibly affected the shape, amplitude, and frequency of the slow waves. Similar alterations were observed in NKCC1 knockout mice. These data support the hypothesis that NKCC1 expressed in myenteric ICC is involved in the mechanism of slow waves in the murine jejunum.

Peripheral pacemakers and patterns of slow wave propagation in the canine small intestine in vivo

In an anesthetized, open-abdomen, canine model, the propagation pattern of the slow wave and its direction, velocity, amplitude, and frequency were investigated in the small intestine of 8 dogs. Electrical recordings were made using a 240-electrode array from 5 different sites, spanning the length of the small intestine. The majority of slow waves propagated uniformly and aborally (84%). In several cases, however, other patterns were found including propagation in the oral direction (11%) and propagation block (2%). In addition, in 69 cases (3%), a slow wave was initiated at a local site beneath the electrode array. Such peripheral pacemakers were found throughout the entire intestine. The frequency, velocity, and amplitude of slow waves were highest in the duodenum and gradually declined along the intestine reaching lowest values in the distal ileum (from 17.4+/-1.7 c/min to 12.2+/-0.7 c/min; 10.5+/-2.4 cm/s to 0.8+/-0.2 cm/s, and 1.20+/-0.35 mV to 0.31+/-0.10 mV, respectively; all p<0.001). Consequently, the wavelength of the slow wave was strongly reduced from 36.4+/-0.8 cm to 3.7 +/- 0.1 cm (p<0.001). We conclude that the patterns of slow wave propagation are usually, though not always, uniform in the canine small intestine and that the gradient in the wavelength will influence the patterns of local contractions.

Longitudinal and circumferential spike patches in the canine small intestine in vivo

In an open-abdominal anesthetized and fasted canine model of the intact small intestine, the presence, location, shape, and frequency of spike patches were investigated. Recordings were performed with a 240-electrode array (24 x 10, 2-mm interelectrode distance) from several sites sequentially, spanning the whole length of the small intestine. All 240 electrograms were recorded simultaneously during periods of 5 min and were analyzed to reconstruct the origin and propagation of individual spikes. At every level in the small intestine, spikes propagated in all directions before stopping abruptly, thereby activating a circumscribed area termed a "patch." Two types of spikes were found: longitudinal spikes, which propagated predominantly in the longitudinal direction and occurred most often in the duodenum, and a second type, circumferential spikes, which propagated predominantly in the circular direction and occurred much more frequently in the jejunum and ileum. Circumferential spikes conducted faster than longitudinal spikes (17 +/- 6 and 7 +/- 2 cm/s, respectively; P < 0.001). Circumferential spikes originated in >90% of all cases from the antimesenteric border, whereas longitudinal spikes were initiated all around the circumference of the intestinal tube. Finally, the spatial sequence of spike patches after the slow wave was very irregular in the upper part of the intestine but much more regular in the lower part. In conclusion, spikes and spike patches occur throughout the small intestine, whereas their type, sites of origin, extent of propagation, and frequencies of occurrence differ along the length of the small intestine, suggesting differences in local patterns of motility.

Cyclosporine increases the intracellular free calcium concentration in electrically paced isolated rat cardiomyocytes

The effect of cyclosporine on the mean cytoplasmic free calcium concentration in electrically paced single cardiomyocytes from adult rats was studied. Cardiac myocytes were paced by electrical field stimulation with either 2 or 3 Hz in the presence of 5 micrograms/ml cyclosporine or the solvent cremophor. Exposure to cyclosporine during 40 minutes of electrical pacing caused irreversible hypercontracture in most cells, only 22.1% +/- 1.2% (mean +/- SEM) remained rod-shaped versus 64.1% +/- 3.2% in the solvent (p = 0.01). The cytoplasmic free calcium concentration was measured by means of digital image processing of fura-2 fluorescence. Electrical field stimulation increased the cytoplasmic free calcium from 69.7 +/- 5.4 to 124.9 +/- 24.5 nmol/L Ca2+ in the presence of the solvent and from 84.2 +/- 25.4 to 250.1 +/- 55.9 nmol/L in the presence of cyclosporine (p = 0.036 versus solvent). The data provide direct evidence that cyclosporine enhances the cytoplasmic free calcium concentration in single paced rat cardiomyocytes. These findings may be of importance in the consideration of a possible cardiotoxicity of cyclosporine.

Isolated rat cardiac myocytes as an experimental model to study calcium overload: the effect of calcium-entry blockers

Calcium overload and the effect of a series of calcium-entry blockers were studied in isolated adult cardiac myocytes from the rat challenged with veratrine. The isolation procedure resulted in a high yield of individual rod shaped, calcium tolerant myocytes. After incubation with veratrine, an alkaloid which induces both sodium and calcium influx, 93% of the myocytes became calcium intolerant: the quiescent rod shaped cells vigorously contracted after 30 sec of contact with veratrine and contracture (round cells) ensued within 1 min. Exposure for 30 min to various doses of calcium-entry blockers prior to veratrine addition resulted in the prevention of contracture, the degree of protection depending on the type and the concentration of calcium-entry blocker. Among the different calcium-entry blockers tested, the diarylalkylpiperazines lidoflazine, cinnarizine and flunarizine were protective from the 10(-7) M concentration onwards. Nicardipine was protective at the 10(-6) M and 10(-5) M concentrations, verapamil at 10(-5)M only while other blockers of the "slow channel" type (diltiazem and nifedipine) were not protective in the concentration range tested. This study shows that isolated myocytes represent a valid model for pharmacological investigations. The results with the calcium-entry blockers stress the heterogeneity of the different series of calcium-entry blockers.