Low molecular-weight G-actin binding proteins involved in the regulation of actin assembly during myofibrillogenesis

We previously demonstrated that small G-actin binding proteins, cofilin, ADF and profilin, are involved in the actin dynamics during myofibrillogenesis (OBINATA, T. (1993). Int. Rev. Cytol., 143: 153-189.). To better understand how they are responsible for the regulation of actin assembly, the amounts of the actin-binding proteins were quantified by means of quantitative immunoblotting and compared with that of G-actin pool. The sum of the amounts of cofilin, ADF and profilin was insufficient at early developmental stages but sufficient at later stages to account for the pool of G-actin in muscle cells. We detected expression of thymosin beta 4 at a considerable level in young embryonic but not in adult skeletal muscles. We, therefore, conclude that the G-actin pool in young embryonic skeletal muscle is mainly due to cofilin, ADF, profilin and thymosin beta 4. Switching from a non-muscle-type (NM-) cofilin to a muscle-type (M-) cofilin was observed during muscle development of mammals. In order to clarify cofilin-dependent regulation of actin assembly in muscle cells, cofilin tagged with fluorescence dyes was introduced into C2 myoblasts by a micro injection method. The exogeneous cofilin, but not ADF, caused quick disassembly of actin filaments and accumulated in furrow region of dividing cells. The analogs of the unphosphorylated form (A3-cofilin) and the phosphorylated form (D3-cofilin) were prepared by converting Ser3, a regulatory phosphorylation site, to Ala or Asp. When A3-cofilin and D3-cofilin were injected into living cells, the former was concentrated at the membrane ruffles and cleavage furrow, while the latter showed only diffuse distribution in the cytoplasm. These results suggest that the subcellular distribution of cofilin as well as its interaction with actin in vivo is regulated by its phosphorylation and dephosphorylation.

GABAergic neurons in the embryonic olfactory pit/vomeronasal organ: maintenance of functional GABAergic synapses in olfactory explants

In previous work, we showed a robust gamma-aminobutyric acid (GABAergic) synaptic input onto embryonic luteinizing hormone-releasing hormone (LHRH) neurons maintained in olfactory explants. In this study, we identify GABAergic neurons in olfactory pit (OP) of embryonic mice in vivo and study, using patch-pipet whole-cell current and voltage clamp techniques, synaptic interactions of these neurons in explant cultures. In vivo, glutamate decarboxylase (GAD, the enzyme which synthesizes GABA) mRNA was first detected in nasal regions on Embryonic Day (E) 11.5. From E12.5 to E13.5, robust GAD expression was localized to cells primarily in the ventral aspect of the OP. GAD mRNA was not detected over dorsally located cells in olfactory sensory or respiratory epithelium. In addition, GAD mRNA was not observed in cells along olfactory axons. GAD mRNA was dramatically reduced in the OP/vomeronasal organ by E16.5. Using antibodies against both GABA and GAD, immunopositive axonal-like tracts were detected in the nasal septum on E12.5. GABAergic staining decreased by E13.5. To examine synaptic interactions of these GABAergic cells, embryonic olfactory explants were generated and maintained in serum-free media. As explants spread, neuron-like cells migrated into the periphery, sometimes forming ganglion-like clusters. Cells were recorded, marked intracellularly with Lucifer Yellow and post-fixation, immunocytochemically examined. Forty-six cells, typically multipolar, were GABAergic, had resting potentials around -50 mV, and exhibited spontaneous action potentials which were generated by spontaneous depolarizing GABAergic (GABAA) synaptic activity. OP neurons depolarized in response to GABA by increasing Cl- conductance. The biophysical properties of OP-derived GABAergic neurons were distinct from those reported for olfactory receptor neurons but similar to embryonic LHRH neurons. However, unlike LHRH neurons, GABAergic neurons did not migrate large distances in olfactory explants or appear to leave the olfactory pit in vivo.

Purification and characterization of rhesus monkey liver amido hydrolases and their roles in the metabolic polymorphism for E6123, a platelet-activating factor receptor antagonist

We previously showed that a polymorphism for E6123 [(S)-(+)-6- (2-chlorophenyl)-3-cyclopropanecarbonyl-8,11-dimethyl-2,3,4,5- tetrahydro-8H-pyrido[4',3':4,5]thieno[3,2-f][1,2,4]triazolo[4,3-a] [1,4]diazepine] metabolism exists only in rhesus monkeys. In the present study, we purified, from rhesus monkey hepatic microsomes, three amido hydrolases that are involved in the metabolic polymorphism. Two forms of amido hydrolase from an extensive metabolizer and one from a poor metabolizer were purified by Q-Sepharose Fast Flow, Red A-agarose, octylamino-Sepharose 4B, and hydroxyapatite-Ultrogel chromatography, after solubilization with Lubrol. The three purified enzymes had the same molecular mass (47 kDa), and their amino-terminal amino acid sequences were identical. The enzymes were different from various known carboxylesterases in terms of substrate specificity, molecular mass, and amino-terminal amino acid sequence. They resembled arylacetamide deacetylase from human hepatic microsomes with respect to molecular mass and amino-terminal amino acid sequence. The KM values of the high and low affinity enzymes in the extensive metabolizer and the sole enzyme in the poor metabolizer were 37.6, 73.0, and 76.5 microM, respectively. The Vmax values were 3312.4, 504.8, and 427.9 pmol/min/mg of protein, respectively. The high affinity enzyme in extensive metabolizer appears to be quite distinct, whereas the low affinity enzyme in extensive metabolizer in similar or identical to the sole enzyme in poor metabolizer. Thus, the metabolic polymorphism in rhesus monkey may depend upon the existence of the high affinity enzyme in extensive metabolizer.

Accurate expressions for the LP modes in a uniform circular-core curved fiber

Accurate forms for the LP(nm) modes (n = 0 and n ≧ 2) in a uniform circular-core curved fiber are given. We show that the LP(nm) modes (n ≧ 2) are composed of two spatially orthogonal components and that, to the zeroth order, there is no special polarization axis for the LP modes in a uniform circular-core curved fiber.

GABAA receptors modulate early spontaneous excitatory activity in differentiating P19 neurons

P19 embryonic carcinoma (EC) stem cells are pluripotent and are efficiently induced to differentiate into neurons and glia with retinoic acid (RA) treatment. Within 5 days, a substantial number of differentiating P19 cells express gene products that are characteristic of a neuronal phenotype. P19 neurons were used as a model to explore the relationship between neuronal "differentiation" in vitro and the acquisition of gamma-aminobutyric acid (GABAA) receptors and functional GABA responses. Pulse-labeling experiments using bromodeoxyuridine indicated that all neurons had become postmitotic within 3-4 days after treatment with RA. This was confirmed by a reduction in the immunocytochemical detection of the undifferentiated stem cell antigen SSEA-1. Subsequently, a transient expression of nestin was observed during the first 5 days in vitro (DIV) after exposure to RA. By 5-10 DIV after RA, a significant number of neurons (approximately 80-90%) expressed immunocytochemically detectable glutamate decarboxylase and GABA coincident with the acquisition of membrane binding sites for tetanus toxin. These phenotypic markers were maintained for > 30 DIV after RA. Under current-clamp conditions, random, low-amplitude, spontaneous electrical activity appeared in neurons within the first few days after RA treatment and this was blocked by the specific GABAA receptor antagonist bicuculline. Thereafter, the appearance and progressive increases in the frequency of spontaneous action potentials in P19 neurons were observed that were similarly attenuated by bicuculline. In neurons > 5 DIV after RA, exogenous application of GABA elicited similar action potentials. The onset of excitatory responses to GABA or muscimol in voltage-clamped neurons appeared immediately after the cessation of neuronal mitosis and before the previously reported acquisition of responses to glutamate. In fura-2 imaging studies, the exogenous application of GABA resulted in neuron-specific increases in intracellular Ca2+. Thus, P19 neurons provide an in vitro model for the study of the early acquisition and properties of electrical excitability to GABA and the expression of functional GABAA receptors.

Restriction-modification systems as genomic parasites in competition for specific sequences

Restriction-modification (RM) systems are believed to have evolved to protect cells from foreign DNA. However, this hypothesis may not be sufficient to explain the diversity and specificity in sequence recognition, as well as other properties, of these systems. We report that the EcoRI restriction endonuclease-modification methylase (rm) gene pair stabilizes plasmids that carry it and that this stabilization is blocked by an RM of the same sequence specificity (EcoRI or its isoschizomer, Rsr I) but not by an RM of a different specificity (PaeR7I) on another plasmid. The PaeR7I rm likewise stabilizes plasmids, unless an rm gene pair with identical sequence specificity is present. Our analysis supports the following model for stabilization and incompatibility: the descendants of cells that have lost an rm gene pair expose the recognition sites in their chromosomes to lethal attack by any remaining restriction enzymes unless modification by another RM system of the same specificity protects these sites. Competition for specific sequences among these selfish genes may have generated the great diversity and specificity in sequence recognition among RM systems. Such altruistic suicide strategies, similar to those found in virus-infected cells, may have allowed selfish RM systems to spread by effectively competing with other selfish genes.

Endogenous bone-resorbing factors in estrogen deficiency: cooperative effects of IL-1 and IL-6

Estrogen deficiency causes a marked bone loss by stimulating osteoclastic bone resorption. To explore the endogenous bone-resorbing factors involved in estrogen deficiency, we examined the bone-resorbing activity present in the supernatant fraction of mouse bone marrow collected from ovariectomized (OVX) mice. Adding bone marrow supernatants at 20-80% to organ cultures of mouse long bones dose-dependently stimulated bone resorption. The endogenous bone-resorbing activity present in bone marrow supernatants from OVX mice was much higher than that from sham-operated mice 2-4 weeks after surgery, and it was significantly diminished by indomethacin in vitro. Anti-IL-1 alpha antibody completely neutralized the bone-resorbing activity present in bone marrow supernatants from OVX mice. Antibodies against IL-1 beta, IL-6, and IL-6 receptors also neutralized it, but partially. The concentration of IL-1 alpha measured by ELISA was much higher in bone marrow supernatants than in sera, but it was not appreciably changed before or after OVX. The concentration of IL-1 beta in bone marrow supernatants from OVX mice was less than the detection limit. OVX stimulated IL-1 activity in bone marrow supernatants measured by means of the proliferation of thymocytes. However, the level of IL-1 alpha present in bone marrow supernatants from OVX mice was insufficient to stimulate bone resorption. Compared with the serum concentration, bone marrow supernatants contained a much higher level of IL-6 as well, and it was further increased by OVX. However, IL-6 alone present in bone marrow supernatants from OVX mice again did not stimulate bone resorption.(ABSTRACT TRUNCATED AT 250 WORDS)

A sporadic case of very slow progressive leukodystrophy involving the cerebellar peduncles

We describe a patient with infantile onset leukodystrophy involving the cerebellar peduncles. She had mild mental retardation, spastic diplegia and mild cerebellar ataxia. The peripheral nerves seemed to be normal. The characteristic MRI findings in this case were extensive lesions of the white matter involving the cerebellar peduncles. In addition there was ventricular enlargement with a markedly decreased volume of the white matter and a hypoplastic corpus callosum. The clinical and laboratory findings imply that the white matter lesions in this patient were the result of delayed myelination rather than demyelination. The patient was evaluated for known metabolic and degenerative diseases, but no abnormalities were observed. Her symptoms and neuroimaging findings did not fit the criteria for any defined leukodystrophy.

A case of dyskinetic cerebral palsy resembling post-anoxic action myoclonus

Myoclonus after brain anoxia is more commonly observed in adults. Perinatal anoxia, however, on rare occasions causes myoclonus as the main neurologic abnormality. In this paper we described a case of cerebral palsy complicated by chorea and tremulous movements of the foot in which there were no risk factors except perinatal asphyxia. The patient had unique symptoms, action myoclonus associated with the movements of hyperkinésie volitionnelle. This case illustrated two points. One is that abnormal involuntary movements attributed to perinatal brain insults had changed as the brain matured. The other is that some movements were very similar to those of the post-anoxic action myoclonus, commonly seen in patients who sustain brain damage in adulthood.

[Symmetrical thalamic lesions due to perinatal brain damage]

There have been many reports concerning cases with basal ganglionic and thalamic lesions due to neonatal hypoxic-ischemic encephalopathy (HIE), which are considered as a clinicopathological syndrome. But the clinical symptoms and extension of the brain damage varied from case to case. We previously reported seven cases with bilateral basal ganglionic and thalamic lesions (BBTL) due to neonatal HIE. The affected lesions were posterior putamen, lateral thalami, hippocampus and perirolandic cortex. Now, we have experienced two cases who presented symmetrical thalamic lesions (STL) with involvement of the brainstem and periventricular white matter due to neonatal HIE. Of these lesions of the basal ganglia and thalamus, STL comprised calcification and atrophy of the bilateral thalami, and BBTL comprised cystic lesions of the bilateral putamen and thalami. The cerebral lesion in the cases of BBTL were observed in the perirolandic cortex, which is a watershed area of the main vascular territories. While the cerebral lesion in the cases of STL were found in the periventricular white matter, which is a watershed area in premature babies. The brainstem was more severely injured in the case of STL than BBTL. The distribution of the affected lesions suggested that the cases with STL had a different clinicopathological syndrome from those with BBTL. We discussed the developmental mechanism of the cases.

[Pattern of the brain damages and its developmental mechanisms in monozygotic twins]

Neurologic morbidity is observed more frequently in twins than in singletons. Low birthweight and premature birth are observed more frequently in twins but cannot always explain the cause of cerebral palsy, although circumstances related to twinning may cause brain damage. We attempted to select the patients whose brain damages might be caused by circumstances related to twinning and discussed the developmental mechanisms of their brain damages. We divided the cases into 3 groups. One comprised the monozygotic (MZ) twins whose co-twins had died. The second comprised the MZ twins with the complication of the twin-twin transfusion syndrome or discordant twins. The third comprised the MZ twins with concordant co-twins. We postulated that group I and II had complication of the disturbance of fetal circulation, but group III did not. Hydranencephaly (group I) and polymicrogyria (group II) might develop when the disruption occurs at an intermediate stage of morphogenesis (before the 6th month of gestation). In the cases with cerebral infarction (group I), the distribution of the lesions were related to the main vascular territories of the mature form, might be caused by occlusion of blood vessels associated with intrauterine disseminated intravascular coagulation. In the cases of MCE (group I), multiple cavities are present mainly in the white matter, the gray matter having a tendency to be spared. As the distribution of the cavities is not related to the main vascular territories, it was less likely that the lesions was produced by occluded vessels. The death of one fetus might cause severe blood deprivation, leading to hypoxic-ischemic brain insults in the surviving fetus.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical and synaptic properties of embryonic luteinizing hormone-releasing hormone neurons in explant cultures

Voltage- and ligand-activated channels in embryonic neurons containing luteinizing hormone-releasing hormone (LHRH) were studied by patch-pipette, whole-cell current and voltage clamp techniques. LHRH neurons were maintained in explant cultures derived from olfactory pit regions of embryonic mice. Cells were marked intracellularly with Lucifer yellow following recording. Sixty-two cells were unequivocally identified as LHRH neurons by Lucifer yellow and LHRH immunocytochemistry. The cultured LHRH neurons had resting potentials around -50 mV, exhibited spontaneous discharges generated by intrinsic and/or synaptic activities and contained a time-dependent inward rectifier (Iir). Voltage clamp analysis of ionic currents in the LHRH neuron soma revealed a tetrodotoxin-sensitive Na+ current (INa) and two major types of K+ currents, a transient current (IA), a delayed rectifier current (IK) and low- and high-voltage-activated Ca2+ currents. Spontaneous depolarizing synaptic potentials and depolarizations induced by direct application of gamma-aminobutyrate were both inhibited by picrotoxin or bicuculline, demonstrating the presence of functional gamma-aminobutyrate type A synapses on these neurons. Responses to glutamate were found in LHRH neurons in older cultures. Thus, embryonic LHRH neurons not yet positioned in their postnatal environment in the forebrain contained a highly differentiated repertoire of voltage- and ligand-gated channels.

Selfish behavior of restriction-modification systems

Plasmids carrying gene pairs encoding type II DNA restriction endonucleases and their cognate modification enzymes were shown to have increased stability in Escherichia coli. The descendants of cells that had lost these genes appeared unable to modify a sufficient number of recognition sites in their chromosomes to protect them from lethal attack by the remaining restriction enzyme molecules. The capacity of these genes to act as a selfish symbiont is likely to have contributed to the evolution of restriction-modification gene pairs.

[A case of spastic paraparesis, mental retardation and thinning of corpus callosum]

There are several reports of the patients who have peculiar clinical presentation, that is, spastic paraparesis, mental disturbance and thinning of corpus callosum. We presented a sporadic case with similar symptoms. He was born by normal vaginal delivery without problems from consanguineous parents. His development had delayed since his infantile period. He started to have spasticity of the legs at the age 13 years and it worsened with advancing age. On examination at age 19, he was mentally slow, his full-scale IQ being 35. The tone in the arms was slightly increased and marked in the legs. The finger to nose test caused mild dysmetria. Rest of the neurological examinations were normal. MRI demonstrated characteristic thinning of corpus callosum, dominant in anterior portion. In addition, it showed wide cavum vergae and cavum septi pellucidi, and abnormal high intensity in periventricular white matter. The findings of MRI were possibly suggestive of the static developmental disturbance of brain.

Effects of cofilin on actin filamentous structures in cultured muscle cells. Intracellular regulation of cofilin action

The previous investigation (Abe et al. (1989) J. Biochem. 106, 696–702) suggested that cofilin is deeply involved in the regulation of actin assembly in developing skeletal muscle. In this study, to examine further the function of cofilin in living myogenic cells in culture, recombinant cofilin having extra Cys residues at the N terminus was produced in Escherichia coli and was labeled with tetramethylrhodamine-iodoacetamide (IATMR). When the cofilin labeled with IATMR (IATMR-cofilin) was introduced into myogenic cells, actin filaments in the cytoplasm or nascent myofibrils were promptly disrupted, and many cytoplasmic rods which contained both IATMR-cofilin and actin were generated. Sarcomeric myofibrillar structures were not disrupted but tropomyosin was dissociated from the structures by the exogenous cofilin, and the IATMR-cofilin became localized in I-band regions. 24 hours after the injection, however, the actin-cofilin rods disappeared completely and the IATMR-cofilin became diffused in the cytoplasm as endogenous cofilin. Concomitantly, actin filaments were recovered and tropomyosin was re-associated with sarcomeric I-bands. At this point, the IATMR-cofilin in the cells still retained the functional activity to form intranuclear actin-cofilin rods in response to stimulation by DMSO just as endogenous cofilin. FITC-labeled actin introduced into myogenic cells at first failed to assemble into filamentous structures in the presence of the exogenous cofilin, but was gradually incorporated into myofibrils with time. The drastic effects of the exogenous cofilin on actin assembly were suppressed by phosphatidylinositol 4,5-bisphosphate (PIP2). These results indicate that the exogenous cofilin is active and alters actin dynamics remarkably in muscle cells, but its activity in the cytoplasm gradually becomes regulated by the action of some factors including PIP2-binding.

Concentration of cofilin, a small actin-binding protein, at the cleavage furrow during cytokinesis

Cofilin is a small actin-binding protein which regulates actin polymerization in a pH-dependent manner. Immunofluorescence microscopy with a monoclonal antibody for cofilin revealed that this protein is temporarily concentrated at the contractile ring during cytokinesis. Cofilin appeared to accumulate rapidly at the contractile ring during late stages of furrowing, and was finally enriched at the midbody. The concentration of cofilin at the contractile ring was observed in several kinds of cultured cells. Furthermore, cofilin introduced into living cells by a microinjection method was also concentrated at the contractile ring. These results suggest that cofilin is involved in actin reorganization during cytokinesis.

Evidence for conservative (two-progeny) DNA double-strand break repair

The double-strand break repair models for homologous recombination propose that a double-strand break in a duplex DNA segment is repaired by gene conversion copying a homologous DNA segment. This is a type of conservative recombination, or two-progeny recombination, which generates two duplex DNA segments from two duplex DNA segments. Transformation with a plasmid carrying a double-strand gap and an intact homologous DNA segment resulted in products expected from such conservative (two-progeny) repair in Escherichia coli cells with active E. coli RecE pathway (recBC sbcA) or with active bacteriophage lambda Red pathway. Apparently conservative double-strand break repair, however, might result from successive events of nonconservative recombination, or one-progeny recombination, which generates only one recombinant duplex DNA segment from two segments, involving multiple plasmid molecules. Contribution of such intermolecular recombination was evaluated by transformation with a mixture of two isogenic parental plasmids marked with a restriction site polymorphism. Most of the gap repair products were from intramolecular and, therefore, conservative (two-progeny) reaction under the conditions chosen. Most were conservative even in the absence of RecA protein. The double-strand gap repair reaction was not affected by inversion of the unidirectional replication origin on the plasmid. These results demonstrate the presence of the conservative (two-progeny) double-strand break repair mechanism. These experiments do not rule out the occurrence of nonconservative (one-progeny) recombination since we set up experimental conditions that should favor detection of conservative (two-progeny) recombination.

Thymine starvation-induced structural changes in Escherichia coli DNA. Detection by pulsed field gel electrophoresis and evidence for involvement of homologous recombination

Effect of thymine starvation on Escherichia coli DNA was investigated by using pulsed field gel electrophoresis combined with cell lysis in agarose gel. Post-lysis treatment with restriction enzymes generating relatively large fragments (NheI, SpeI or XbaI) revealed peculiar electrophoretic profiles specific for thymine-starved cells. Thus, a substantial portion of the DNA remained in the origin of electrophoresis (non-migrating DNA), and the amounts of the migrating fragments correspondingly decreased in an inverse relation to the map distance between the origin of replication (oriC) and each fragment. The formation of non-migrating DNA seems to depend upon the presence of replicated portions of the chromosome (sister duplexes), as judged by the effect of a preincubation at the non-permissive temperature in a dnaA(Ts) mutant. Electron microscopy showed that the non-migrating fraction of DNA was enriched with such structures as single-stranded tails or gaps and branchings with single-stranded arms. It was also found that the appearance of non-migrating DNA was highly dependent on the functional recA gene and moderately on certain RecF-family genes. These results strongly suggest that homologous recombination between sister duplexes is involved in the formation of the peculiar structures found in non-migrating DNA. A possible causal relationship between the formation of non-migrating DNA and viability loss (thymineless death) is also discussed.

[Epilepsy in patient with structural autosomal abnormality]

Few cases have been reported on the structural autosomal abnormality (SAA) focusing on epilepsy excluding those of Down syndrome and Klinefelter syndrome. We investigated patients who had SAA with special reference to epilepsy. Various types of epilepsy were observed in its severity in our cases as well as previously reported cases. There was no correlation between the degree of mental retardation, motor dysfunction, brain damage on CT scan, and severity of epilepsy. Some cases had brain dysplasia, such as agenesis of corpus callosum, pachygyria, and mega cisterna magna. No correlation was found between these brain dysplasia and severity of epilepsy. It is important for a pediatrician to find a common epileptic syndrome or EEG abnormality in a SAA. An observation of symptoms in patients with the same chromosomal deletion or duplication will lead to identification of responsible gene for an epileptic symptom.

Estrogen deficiency stimulates B lymphopoiesis in mouse bone marrow

We have found that an estrogen deficiency causes a marked increase in bone marrow cells. To examine the effect of estrogen on hemopoiesis, we characterized the increased population of bone marrow cells after ovariectomy (OVX). In OVX mice, the percentage of myeloid cells and granulocytes was decreased, whereas that of B220-positive B lymphocytes was selectively increased 2-4 wk after surgery. The total number of myeloid cells and granulocytes did not change appreciably, but that of B220-positive cells was greatly increased by OVX. When OVX mice were treated with estrogen, the increased B lymphopoiesis returned to normal. B220-positive cells were classified into two subpopulations, B220low and B220high. The majority of the B220low cells were negative for the IgM mu chain, whereas most of the B220high cells were mu-positive. OVX selectively increased the precursors of B lymphocytes identified by B220low. mu-negative phenotype, suggesting that an estrogen deficiency stimulates accumulation of B lymphocyte precursors. When bone marrow-derived stromal cells (ST2) were pretreated with estrogen then co-cultured with bone marrow cells in the presence of estrogen, the stromal cell-dependent B lymphopoiesis was greatly inhibited. The present study suggests that estrogen plays an important role in the regulation of B lymphocyte development in mouse bone marrow.

Prophylactic efficacy of milbemycin oxime against multiple infection of dogs with Dirofilaria immitis

In order to examine the prophylactic effects of milbemycin oxime (MO) against Dirofilaria immitis infection, experiments were carried out under multiple infection with D. immitis. Ten filaria-free beagles of age 4 to 8 months were each inoculated with a total number of 480 larvae 12 times at intervals of 15 days over a period of 6 months, and MO was given monthly for the 6 months at a dose of 0.25 mg/kg. The infection rate in the medicated group of dogs was nil, this suggesting complete protection of the infection, while in the non-medicated control group it ranged from 6.5 to 14.8% (mean, 11.4%).

Monozygous twin with polymicrogyria and normal co-twin

Monozygous twinning has been associated with brain lesions such as holoprosencephaly, hydranencephaly, multicystic encephalomalacia, and porencephaly. Polymicrogyria is rare but has been reported in autopsied cases. We present a monozygotic twin with complicating twin-twin transfusion syndrome, the donor exhibiting normal psychomotor development and the recipient psychomotor delay associated with the brain anomaly, polymicrogyria. The brain anomaly might be due to blood pressure instability or a circulatory disturbance resulting from increased coagulability due to polycythemia.

[Clinical consideration of patients with neonatal bilateral basal ganglia-thalamic lesion due to hypoxic ischemic encephalopathy]

We describe herein the clinical symptoms, clinical course and results of investigation of 7 patients with bilateral basal ganglia-thalamic lesions (BBTL). All patients had spastic quadriplegia with rigidity. They were unable to sit and turn over. They could follow objects, turn head towards a sound and recognize parents to some degree. They were all evaluated as having the most severe degree of disability (Oshima's classification 1). They all had dysphagia and 2 patients had a episode of bradycardia and hypothermia, which might be evidences of brain stem disorders. Muscle hypertonia, vomiting, hematemesis and obstructive respiration, which were the major complications for the patients, worsened with age. High percentage of histories of birth asphyxia and poor feeding in the neonatal period suggested that perinatal brain insults might be one of the important factors for developing BBTL. It seemed to be difficult to explain that such diffuse brain injuries in our cases were caused by only the insults during parturition. Brain insults during parturition as well as prenatal factors probably participate in developing BBTL. Although the cerebrum of the patients seem to be relatively preserved in the images of head CT-scan, MRI of the patients revealed diffuse brain lesions. All of five patients tested had an abnormal auditory brain stem response (ABR). These investigations demonstrated that patients with BBTL have diffuse brain damage including brain stem. Further observation is needed to verify the mechanisms of development and the time of onset of BBTL.

DNA double-strand break repair: genetic determinants of flanking crossing-over

Whether or not homologous interaction of two DNA molecules results in crossing-over of the flanking sequences is an important decision in view of genome organization. Several homologous recombination models, including the double-strand break repair models, explain this decision as choice between two alternative modes of resolution of Holliday-type intermediates. We have demonstrated that a double-strand gap can be repaired through gene conversion copying a homologous duplex, as predicted by the double-strand break repair models, in the RecE pathway of Escherichia coli. This gap repair is often accompanied by crossing-over of the flanking sequences. Mutations in ruvC and recG, whose products interact with Holliday structures in vitro, do not block double-strand gap repair or its association with flanking crossing-over. However, two mutations in the recJ gene, which encodes a single-strand 5'-->3' exonuclease, severely decrease association of flanking crossing-over. Two mutations in the recQ gene, which encodes a helicase, moderately decrease association of flanking crossing-over by themselves and suppress the severe effect of a recJ mutation. Similar relationships of recJ and recQ mutations are observed in cell survival after ultraviolet light irradiation, gamma-ray irradiation, and H2O2 treatment. We discuss how cooperation of the recQ gene product and the recJ gene product brings about double-strand break repair accompanied by flanking crossing-over. We also discuss how this reaction is related to repair of chromosome damages.

Development of radioimmunoassay for the novel platelet activating factor receptor antagonist, E6123, and its application to pharmacokinetics in laboratory animals

A direct radioimmunoassay for the determination of E6123, a novel antagonist of platelet activating factor (PAF) receptor, was developed in order to study the pharmacokinetics at low dose. This procedure used [3H]E6123 as the radioligand and an antiserum obtained from rabbits immunized with the hapten covalently bound to bovine serum albumin. M1B, one of the main metabolites of E6123, exhibited cross-reactivity with antisera. But this metabolite had no effect on measurements of E6123, because the amount of M1B in plasma radioactivity after administration of [14C]E6123 to dogs and monkeys was low. The sensitivity limit of this assay was 25 pg/ml of plasma when 0.1 ml of plasma was used and the assay showed good accuracy and high precision. The validity of the radioimmunoassay was demonstrated by comparative analysis of a number of samples after oral and intravenous administration (1.0 mg/kg) by HPLC-UV method (r = 0.972-0.984, slope = 1.0314-1.2143). The pharmacokinetics of E6123 was studied at a dose of 30 micrograms/kg. After intravenous administration, the plasma concentration-time curves in all species fitted a two-compartment model and the terminal half-lives in guinea pigs, dogs and monkeys (both poor and extensive metabolizers) were 4.77, 1.71, 5.34 and 1.07 h, respectively. After oral administration, the maximum plasma concentrations were obtained within 0.83-3.00 h and the half-life for each animal was almost the same as that after intravenous administration. The mean bioavailabilities of E6123 in guinea pigs, dogs and monkeys (poor and extensive metabolizers) were 106.9, 45.7, 59.1 and 22.8%, respectively.

Involvement of RecE exonuclease and RecT annealing protein in DNA double-strand break repair by homologous recombination

We demonstrated that a double-stranded (ds) gap in DNA is repaired by a gene conversion mechanism in an Escherichia coli recBC sbcA23 strain, as predicted by the ds break repair models for homologous recombination. The sbcA mutation is known to induce several gene products encoded on the Rac prophage present in most strains of E. coli K-12. These include exonuclease VIII (Exo VIII), a 5' to 3' exonuclease working from the end of a duplex DNA, and RecT, an annealing protein. We found that a rac- strain (lacking the Rac prophage) cannot support this repair. A plasmid carrying part of the Rac prophage supported highly efficient ds gap repair activity in a rac- strain, but two ExoVIII+ recT- plasmids did not. The recE159 mutation that blocks ds gap repair was found to be recT+, since these ExoVIII+ recT- plasmids complemented the recE159 mutation in repair of ultraviolet light damage. From these observations, we conclude that both ExoVIII and RecT are essential for ds gap repair. We discuss their possible roles in the ds break repair reaction.

Receptor-activated currents in mouse fibroblasts expressing transfected bombesin receptor subtype cDNAs

BALB/c 3T3 cells do not normally express receptors for bombesin-like peptides [bombesin (Bn), gastrin-releasing peptide (GRP), and neuromedin B (NmB)]. Transfection of BALB/c 3T3 cells with complementary DNA-encoding GRP receptors or NmB receptors leads to stable expression of functional GRP receptors (GRP Rt) or NmB receptors (NmB Rt), respectively, which are coupled to cell membrane ion channels. Whole cell current analysis using patch electrodes shows that the activation of these newly expressed receptors induces cation conductance increases, most frequently a Ca(2+)-activated plasma membrane K+ conductance. The dose-response (peak-current) relations of both transfected receptor subtypes were sigmoidal and exhibited threshold activation concentration in the picomole range and the saturation of responses to higher concentrations than 10(-8) M. The GRP Rt responded about equally to GRP, NmB, and Bn when compared at equimolar levels, despite their known difference in binding affinity for the three peptides (GRP, Bn > NmB). In contrast, for the NmB Rt, the NmB was more potent than GRP or Bn. Among four GRP/Bn-receptor antagonists tested, the [D-Phe6]Bn(6-13) ethyl ester suppressed GRP Rt responses at low concentrations (10(-7) M). N-acetyl-GRP-(20-26) amide, [Leu13-psi(CH2NH)-Leu14]Bn, and [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P also blocked GRP Rt responses but at higher concentrations (10(-5) M). However, at these concentrations, these four antagonists had little effect on NmB Rt responses, thereby showing a specificity of these antagonists for the GRP receptors.

Genetic analysis of double-strand break repair in Escherichia coli

We had reported that a double-strand gap (ca. 300 bp long) in a duplex DNA is repaired through gene conversion copying a homologous duplex in a recB21 recC22 sbcA23 strain of Escherichia coli, as predicted on the basis of the double-strand break repair models. We have now examined various mutants for this repair capacity. (i) The recE159 mutation abolishes the reaction in the recB21C22 sbcA23 background. This result is consistent with the hypothesis that exonuclease VIII exposes a 3'-ended single strand from a double-strand break. (ii) Two recA alleles, including a complete deletion, fail to block the repair in this recBC sbcA background. (iii) Mutations in two more SOS-inducible genes, recN and recQ, do not decrease the repair. In addition, a lexA (Ind-) mutation, which blocks SOS induction, does not block the reaction. (iv) The recJ, recF, recO, and recR gene functions are nonessential in this background. (v) The RecBCD enzyme does not abolish the gap repair. We then examined genetic backgrounds other than recBC sbcA, in which the RecE pathway is not active. We failed to detect the double-strand gap repair in a rec+, a recA1, or a recB21 C22 strain, nor did we find the gap repair activity in a recD mutant or in a recB21 C22 sbcB15 sbcC201 mutant. We also failed to detect conservative repair of a simple double-strand break, which was made by restriction cleavage of an inserted linker oligonucleotide, in these backgrounds. We conclude that the RecBCD, RecBCD-, and RecF pathways cannot promote conservative double-strand break repair as the RecE and lambda Red pathways can.

Prophylactic effect of milbemycin oxime against Dirofilaria immitis infection in dogs: optimum dose and administration time

To examine the prophylactic efficacy of milbemycin oxime against Dirofilaria immitis infection, 42 filaria-free beagles were inoculated with 100 infective larvae of the parasite. Milbemycin oxime was administered orally at doses of 0.05 to 1.0 mg/kg body weight one month after inoculation, and at a single dose of 0.25 mg/kg body weight on days 1 to 90 after inoculation. All dogs were euthanized and autopsied to evaluate the prophylactic effect of the drug against D. immitis infection 6 months after inoculation. It was confirmed that a dose of 0.25 mg/kg of milbemycin oxime completely-protected the infection 15 to 60 days after infection.

Pharmacokinetics of a new thienodiazepine platelet activating factor receptor antagonist (E6123) in laboratory animals. Is there a metabolic polymorphism in the rhesus monkey?

1. The pharmacokinetics of E6123, a platelet activating factor receptor antagonist, were studied after i.v. and oral administration to rat, guinea-pig, dog and rhesus monkey. Plasma concentrations of E6123 were determined by h.p.l.c. with UV detection. 2. After i.v. dosing (1 mg/kg), the plasma concentration-time curves fitted a two-compartment model. The half-lives for the terminal phases (t1/2) in rat, dog, and guinea-pig showed very little inter-individual variation, but t1/2 in the monkey (n = 4) varied more than four-fold. The distribution parameters were very similar in rat, dog and monkey (Vc and Vss approx. 1.2 and 1.5 l/kg, respectively) but slightly higher values were found in the guinea-pig, which also showed the lowest plasma protein binding. 3. After oral dosing (1 mg/kg), the maximum plasma concentrations were obtained within 0.3-3.0 h in all species. The half-life for each individual animal was almost the same as that after i.v. dosing. The mean bioavailabilities of E6123 in rat, guinea-pig and dog were about 65, 95 and 81%, respectively, but the values for monkey were again highly variable (range 32-99%). 4. The high variability in the monkey was confirmed by i.v. administration to a further 10 animals. The mean half-lives for the terminal phase in extensive metabolizers (EMs) (n = 4) and poor metabolizers (PMs) (n = 10) were approx. 1 and 4 h, respectively. 5. The rank order for total body clearance of E6123 was: rat > monkey (EMs) > dog > guinea-pig > monkey (PMs).

Metabolic polymorphism of E6123 in rhesus monkey

1. The metabolic polymorphism of a new thienodiazepine platelet activating factor receptor antagonist (E6123) in rhesus monkey was studied in vivo and in vitro. 2. After i.v. dosing of 14C-E6123, the levels of radioactivity in blood, plasma and red blood cells were higher in poor metabolizers (PMs) with AUC(0-24 h) values which were about 1.3-1.5 times higher than those in extensive metabolizers (EMs). 3. After i.v. dosing of 14C-E6123, radioactivity was excreted rapidly by both EMs and PMs. However, EMs excreted the radioactivity mainly in urine whereas, for PMs, radioactivity was excreted fairly equally in urine and faeces. 4. In vivo and in vitro studies demonstrated that the metabolic polymorphism of E6123 in rhesus monkey is caused by a difference in the hydrolysis of an amide side chain. 5. Our results suggested that there are two types of the enzymes which metabolize E6123 by this route in EMs, but only one type in PMs. 6. The low affinity enzyme in EMs might be the same as the enzyme in PMs, indicating that the metabolic polymorphism of E6123 in rhesus monkey could depend on the existence of a high affinity enzyme.

Clinical and laboratory changes after administration of milbemycin oxime in heartworm-free and heartworm-infected dogs

Adverse reactions to oral administration of milbemycin oxime were investigated in heartworm (HW)-free and HW-infected dogs given either the minimal HW prophylactic dose (0.25 mg/kg of body weight) or the hookworm anthelmintic dose (0.5 mg/kg). In 12 HW-free control dogs treated with lactose excipient (100 mg/kg), abnormal signs were not observed. There were no differences between the 2 doses in prevalence of clinical signs of disease and laboratory test results. In 60 HW-free dogs (50 dogs administered the low dose, and 10 dogs given the high dose) and 46 nonmicrofilaremic HW-infected dogs (35 dogs administered the low dose, and 11 dogs given the high dose), only a transient and slight paleness of the visible mucous membranes, intestinal hyperperistalsis, or both were observed in some dogs. In 77 microfilaremic (MF) dogs (41 dogs administered the low dose, and 36 dogs given the high dose), weakness or loss of appetite was observed in 13 dogs (16.9%). Paleness of the visible mucous membranes was observed in 16 dogs (20.8%), intestinal hyperperistalsis was observed in 27 dogs (35.1%), and respiratory signs, such as mild labored respiration, were observed in 13 dogs (16.9%). Dullness of heart sounds was noticed in 4 dogs (5.2%). In 12 (9 dogs administered the low dose, and 3 dogs given the high dose) of 89 MF dogs (13.5%), adult heartworms migrated from the pulmonary arteries to the right atrium, causing signs of caval syndrome, including heart murmurs, jugular pulsations, and weakness. In HW-free dogs, rectal temperature tended to decrease gradually, and heart and respiratory rates were transiently decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Targeted recombination with single-stranded DNA vectors in mammalian cells

We studied the ability of single-stranded DNA (ssDNA) to participate in targeted recombination in mammalian cells. A 5' end-deleted adenine phosphoribosyltransferase (aprt) gene was subcloned into M13 vector, and the resulting ssDNA and its double-stranded DNA (dsDNA) were transfected to APRT-Chinese hamster ovary cells with a deleted aprt gene. APRT+ recombinants with the ssDNA was obtained at a frequency of 3 x 10(-7) per survivor, which was almost equal to that with the double-stranded equivalent. Analysis of the genome in recombinant clones produced by ssDNA revealed that 12 of 14 clones resulted from correction of the deletion in the aprt locus. On the other hand, the locus of the remaining 2 was not corrected; instead, the 5' deletion of the vector was corrected by end extension, followed by integration into random sites of the genome. To exclude the possibility that input ssDNA was converted into its duplex form before participating in a recombination reaction, we compared the frequency of extrachromosomal recombination between noncomplementary ssDNAs, and between one ssDNA and one dsDNA, of two phage vectors. The frequency with the ssDNAs was 0.4 x 10(-5), being 10-fold lower than that observed with the ssDNA and the dsDNA, suggesting that as little as 10% of the transfected ssDNA was converted into duplex forms before the recombination event, hence 90% remained unchanged as single-stranded molecules. Nevertheless, the above finding that ssDNA was as efficient as dsDNA in targeted recombination suggests that ssDNA itself is able to participate directly in targeted recombination reactions in mammalian cells.

Modulation of voltage-activated Ca currents by pain-inducing agents in a dorsal root ganglion neuronal line, F-11

Whole cell currents evoked by pain-inducing agents--bradykinin (Bk), capsaicin (Cap), and reciniferatoxin (RTX), and their modulation of voltage-activated Ca currents were examined in F-11 cells using a patch electrode voltage clamp technique. Most F-11 cells generated action potentials under current clamp if their membrane potentials were held sufficiently negative. Average peak inward Na current (INa) was 100 microA/cm2 and the INa was abolished by 10(-6) M tetrodotoxin. At least two types of Ca currents could be clearly distinguished on the basis of voltage dependency and kinetics; a low threshold transient ICa(t) and a high threshold sustained ICa(l). In addition, another high threshold transient Ca current, presumably ICa(n), was observed. About 30% of the cells produced inward current for these pain-inducing agents, when activated at the membrane holding potential of -70 mV. In some F-11 cells, the amplitude of action potential was observed to increase during 10(-6) M Cap-induced depolarization. Both low and high threshold Ca currents were reduced by 10(-6) M Bk in the majority of the cells. Similarly, both 10(-6) M Cap and 10(-9) M RTX reduced these Ca currents. However, a considerable number of cells showed an initial enhancement followed by reduction in the amplitude of these Ca currents. With higher concentrations of these ligands, all Ca currents were suppressed. Such modulation of voltage-activated Ca currents by pain-inducing agents occurred in both the presence and absence of apparent receptor-activated current flows in the cells. In pertussis toxin (PTX)-treated cells, the inhibitory modulation of Ca currents by pain-inducing agents was suppressed. In contrast, in cholera toxin (CTX)-treated cells, this inhibitory modulation appeared to be enhanced. These data indicate that the inhibitory modulation of Ca channel currents by Cap and RTX, similarly to that of Bk, involves a PTX-sensitive inhibitory G protein (Gi).

Gene conversion in the Escherichia coli RecF pathway: a successive half crossing-over model

Gene conversion--apparently non-reciprocal transfer of sequence information between homologous DNA sequences--has been reported in various organisms. Frequent association of gene conversion with reciprocal exchange (crossing-over) of the flanking sequences in meiosis has formed the basis of the current view that gene conversion reflects events at the site of interaction during homologous recombination. In order to analyze mechanisms of gene conversion and homologous recombination in an Escherichia coli strain with an active RecF pathway (recBC sbcBC), we first established in cells of this strain a plasmid carrying two mutant neo genes, each deleted for a different gene segment, in inverted orientation. We then selected kanamycin-resistant plasmids that had reconstituted an intact neo+ gene by homologous recombination. We found that all the neo+ plasmids from these clones belonged to the gene-conversion type in the sense that they carried one neo+ gene and retained one of the mutant neo genes. This apparent gene conversion was, however, only very rarely accompanied by apparent crossing-over of the flanking sequences. This is in contrast to the case in a rec+ strain or in a strain with an active RecE pathway (recBC sbcA). Our further analyses, especially comparisons with apparent gene conversion in the rec+ strain, led us to propose a mechanism for this biased gene conversion. This "successive half crossing-over model" proposes that the elementary recombinational process is half crossing-over in the sense that it generates only one recombinant DNA duplex molecule, and leaves one or two free end(s), out of two parental DNA duplexes. The resulting free end is, the model assumes, recombinogenic and frequently engages in a second round of half crossing-over with the recombinant duplex. The products resulting from such interaction involving two molecules of the plasmid would be classified as belonging to the gene-conversion type without crossing-over. We constructed a dimeric molecule that mimics the intermediate form hypothesized in this model and introduced it into cells. Biased gene conversion products were obtained in this reconstruction experiment. The half crossing-over mechanism can also explain formation of huge linear multimers of bacterial plasmids, the nature of transcribable recombination products in bacterial conjugation, chromosomal gene conversion not accompanied by flanking exchange (like that in yeast mating-type switching), and antigenic variation in microorganisms.

Hemorrhagic myocardial infarction after reperfusion detected by X-ray CT--experimental and clinical study

The purpose of this study was to determine whether computed tomography (CT) can detect hemorrhagic infarction occurring after intracoronary thrombolytic therapy (ICT) for acute myocardial infarction (AMI). In an experimental study, 12 dogs underwent 2-4 h of left anterior descending artery (LAD) occlusion, followed by reperfusion, and infusion of contrast material into the LAD. After CT examination, the heart was cut into transverse sections. A good correlation was obtained between the CT-enhanced area and the hemorrhagic area in the sliced heart section (r = 0.895, p less than 0.001). In a clinical study, we applied CT immediately after ICT in 25 patients with AMI. In 13 of 25 patients, the CT showed post-ICT myocardial enhancement areas. To evaluate the relationship of the enhancement areas shown by CT to the viability of the myocardium, we compared enhancement areas by CT with the corresponding perfusion defect areas of Thallium-201 imaging (SPECT) one month later. There was no significant correlation between the enhancement areas and perfusion defect areas (r = 0.38, p greater than 0.1). The SPECT defect areas were consistently smaller than the CT enhancement areas. These results indicate that CT can detect hemorrhage into the myocardium after ICT, and that after ICT half the AMI patients showed hemorrhagic infarction. However, hemorrhage did not cause complete deterioration of the myocardium.

Maintenance of LHRH and oxytocin neurons in slice explants cultured in serum-free media: effects of tetrodotoxin on gene expression

A variety of neuroendocrine cells survive and express specific neuropeptide genes for long periods of time in slice explant cultures in the presence of serum. However, before use of these slice explant cultures as experimental models for physiological and pharmacological studies on the regulation of neuropeptide gene expression, it is first necessary to evaluate their characteristics in defined (e.g. serum free) media and to control for the spontaneous electrical and synaptic activity of neurons in these cultures. In this study, brain slices from postnatal day 4 rats were cultured in serum-containing media (SCM) for 12 days to allow thinning, and then maintained in a serum-free, defined media (SFM) for 6 days. Culture slices transferred to SFM appeared healthy and numerous neuroendocrine neurons containing messenger RNA (mRNA) encoding for LHRH and magnocellular neurons containing mRNA encoding for oxytocin (OT) were detected using in situ hybridization histochemistry (ISHH). Each of these neuronal subtypes robustly produced their appropriate gene products as determined by immunocytochemical analysis. Abundant magnocellular OT neurons were found in cultures grown in either SCM or SFM. In contrast, magnocellular vasopressin (VP) neurons were rarely detected under these conditions. Inhibition of spontaneous electrical and synaptic activity in these slice explant cultures was effectively achieved by incubation for the last 2.5 days of culture in the presence of tetrodotoxin (TTX; 10(-6) M). Densitometric single cell analyses after ISHH was performed on both LHRH and OT cells. Comparisons of the density values (corresponding to mRNA levels), from these slice explants, found that: (1) cellular LHRH mRNA levels decreased in the absence of serum, whereas cellular OT mRNA levels did not significantly change under these conditions; (2) the presence of TTX in the media resulted in an overall decrease in cellular LHRH mRNA values in both SCM and SFM, and (3) the OT neurons in these slice cultures appear to be composed of a heterogeneous population, with one cell subtype responding to TTX with an increase in cellular OT mRNA levels. These data show that factors in serum and spontaneous electrical activity can differentially influence mRNA levels of LHRH cells and magnocellular OT neurons in culture.

Whole cell current analyses of pancreatic acinar AR42J cells. II. CCK and receptor-activated membrane currents

Receptor currents generated in response to the application of sulfated octa-cholecystokinin (CCK) and various pancreatic secretagogues were studied in AR42J cells, a rat pancreatic acinar cell line. A whole cell configuration of the patch electrode voltage-clamp technique was utilized in these studies. Over 60% of the cells examined responded to 10(-6) M CCK by generating inward current at a membrane holding potential of -70 mV, accompanied by an increased membrane conductance. The CCK-induced receptor current (ICCK) was typically inactivated within 30 s in the presence of the ligand. The reversal potential (Erev) of the ICCK was approximately 0 mV when recorded in control bathing solution with a pipette containing 154 mM Cl-. When Cl- concentration in the bathing solution or in the recording pipette was modified, the Erev of the ICCK shifted toward the predicted Cl- potential. Na+ and K+ did not show significant contributions to the Erev of ICCK. Hence, the ICCK involves an increased Cl- conductance. This increased Cl- conductance appears to be due to an increase in intracellular Ca2+, since the ICCK could not be recorded from cells using pipettes containing 5 mM EGTA. Application of a Ca2+ ionophore A23187 (5 microM) to cells in control saline induced a similar inward current flow. The source of the Ca2+ involved in the ICCK appears to be mainly intracellular, since the ICCK could be recorded under conditions designed to completely block the voltage-dependent Ca2+ entry. These included exposure of the cells to a Ca2(+)-free saline for a brief period or the presence of 500 microM Cd2+ in the control bathing solution.

Whole cell current analyses of pancreatic acinar AR42J cells. I. Voltage- and Ca(2+)-activated currents

Voltage- and Ca(2+)-activated whole cell currents were studied in AR42J cells, a clonal cell line derived from rat pancreatic acinar cells, using a patch electrode voltage-clamp technique. Four kinds of ionic currents were identified by their ionic dependencies, pharmacological properties, and kinetic parameters: 1) an outward current flow due mainly to a voltage-dependent K(+)-conductance increase, 2) an initial transient inward current due to an Na(+)-conductance increase, 3) transient and long-duration inward current due to a Ca(2+)-conductance increase, and 4) a slowly activating inward current that persists over the duration of the depolarizing pulse and deactivates slowly upon repolarization, producing a slow inward tail current. The slow inward tail current was particularly robust and was interpreted as due to a Ca(2+)-activated Cl(-)-conductance increase, since 1) the generation of this current was blocked by removing the extracellular Ca2+, applying Ca(2+)-channel blockers (Cd2+, nifedipine), or by lowering the intracellular Ca2+ concentration [( Ca2+]i) with EGTA; and 2) the reversal potential (Erev) of the slow inward tail current was close to 0 mV in the control condition (152 mM [Cl-]o/154 mM [Cl-]i), and changes of the [Cl-]o/[Cl )i ratio shifted the Erev toward the predicted Cl- equilibrium potential.

Distinguishing bombesin receptor subtypes using the oocyte assay

Physiological responses to mammalian bombesin-like peptides were studied in Xenopus oocytes injected with mRNA isolated from Swiss 3T3 cells and rat esophagus in order to identify and characterize bombesin receptor subtypes. Both groups respond similarly to either gastrin releasing peptide or neuromedin B, but only the response to neuromedin B in oocytes expressing the esophagus mRNA is not blocked by a specific gastrin releasing peptide receptor antagonist, des-Met-[D-Phe6]Bn(6-13) ethyl ester. Complete desensitization of gastrin releasing peptide-evoked responses in oocytes expressing esophagus mRNA does not abolish neuromedin B-evoked responses. A single application of neuromedin B abolishes responses to subsequently applied gastrin releasing peptide in oocytes expressing esophagus, but not Swiss 3T3, mRNA. RNA blot hybridization studies using a Swiss 3T3 gastrin releasing peptide receptor cDNA probe show no detectable hybridization in esophagus mRNA samples. These data suggest that a gastrin releasing peptide receptor is expressed in the esophagus and that it is distinct from that expressed in Swiss 3T3 cells and may represent a third subtype of mammalian bombesin receptor.

Bombesin-like peptides induce Ca2(+)-activated K+ conductance increases in mouse fibroblasts

Peptide receptor-activated membrane currents were studied in two mouse fibroblast cell lines, Swiss and Balb/c 3T3 cells, using a patch-electrode voltage-clamp technique. About 50% of the Swiss 3T3 cells examined responded to bombesin (Bn; 10(-9) to 10(-6) M), either by inducing outward current flow or inward current flow at the membrane holding potential (Vh) of -60 mV. The outward current type was more common (approximately 70%) than the inward current type (30%). The Bn-induced outward current (IBn) was reversed as the Vh was held to more negative than -90 mV (avg reversal potential, Erev = -82 mV). This Erev was closer to the equilibrium potential for K+ and shifted by altering the extracellular-to-intracellular K+ concentration ratio, in a Nernst-like relationship. The chance of recording this type of IBn was greatly reduced when K+ conductance blockers were present in the bathing solution (i.e., tetraethylammonium, Ba2+) or in the pipette solution (i.e., Cs). It was also reduced by recording with the pipette containing 5-10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Application of Ca2+ ionophore A23187 (5 microM) induced a similar membrane current with conductance increase. Thus the outward IBn in Swiss 3T3 cells appears to be induced by the intracellular Ca2(+)-dependent K+ conductance increase. Applications of bradykinin (Bk), arginine vasopressin (AVP), neuromedin B (NmB), and gastrin releasing peptide (GRP) to Swiss 3T3 cells also induced receptor-activated currents similar to IBn. Balb/c 3T3 cells rarely generated outward currents in response to Bn, GRP, and NmB but did not respond to both AVP and Bk with outward current flows.

cDNA cloning, characterization, and brain region-specific expression of a neuromedin-B-preferring bombesin receptor

Recent binding studies in the central nervous system and other tissues provide evidence that the mammalian bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin-B (NMB), exert their numerous physiological effects through at least two different receptors. We describe the structure and expression of a cloned NMB-preferring bombesin receptor (NMB-R) with properties distinct from a GRP-preferring bombesin receptor (GRP-R) reported previously. In particular, the NMB-R shows higher affinity binding to NMB than to GRP in BALB 3T3 fibroblasts expressing the cloned NMB-R. The distinct regional distribution of NMB-R and GRP-R mRNA in the brain suggests that both bombesin receptor subtypes play independent roles in mediating many of the dramatic effects of bombesin-like peptides in the central nervous system.

Molecular cloning of the bombesin/gastrin-releasing peptide receptor from Swiss 3T3 cells

The mammalian bombesin-like peptides gastrin-releasing peptide (GRP) and neuromedin B regulate numerous and varied cell physiologic processes in various cell types and have also been implicated as autocrine growth factors influencing the pathogenesis and progression of human small cell lung carcinomas. We report here the molecular characterization of the bombesin/GRP receptor. Structural analysis of cDNA clones isolated from Swiss 3T3 murine embryonal fibroblasts shows that the GRP receptor is a member of the guanine nucleotide binding protein-coupled receptor superfamily with seven predicted hydrophobic transmembrane domains. In vitro transcripts from cloned cDNA templates encompassing the predicted protein coding domain, when injected into Xenopus oocytes, resulted in expression of functional GRP receptors. The predicted amino acid sequence of the open reading frame in cDNA clones matches the amino-terminal sequence as well as the sequence of four tryptic fragments isolated from the purified protein. Expression of the GRP receptor cDNA in model systems potentially provides a powerful assay for the development of subtype-specific receptor antagonists that may prove to be of therapeutic importance in human small cell lung carcinoma.

Heat generation associated with synaptic transmission in the mammalian superior cervical ganglion

By use of a thermal detector constructed with a thin polyvinylidene fluoride film (PVDF), heat production in the superior cervical ganglion (SCG) of the guinea pig was examined. A single electric shock applied to the preganglionic nerve evokes a temperature rise of approximately 1.5 x 10(-6) deg. The thermal responses summate when the preganglionic nerve is stimulated repetitively. The amplitude of the thermal response is increased when the preparation is treated with a high Ca2+ medium. Treatment with agents that block ganglionic transmission (high Mg2+, d-tubocurarine, hexamethonium, TTX) reversibly suppresses thermal response. It is thus concluded that the thermal responses described in this paper are generated by the physico-chemical events underlying postsynaptic electrogenesis in the SCG cells.