Different intrafusal fiber composition of spindles in sheep and pig extraocular muscles

Histochemical profiles of intrafusal fibers have been examined in muscle spindles of extraocular muscles of sheep and pig. Results show that in the sheep the intrafusal content presents, in addition to chain fibers, at least one bag1 and one bag2 fiber, whereas in the pig almost all the spindles are one-bag-fiber [corrected] spindles.     

Neuromuscular spindles in bovine foetuses with hereditary muscle fiber hyperplasia

Summary In cattle with genetic hyperplasia of skeletal muscle fibers, foetuses have an increased number of intrafusal muscle fibers in their neuromuscular spindles.     

Ultrastructure of muscle spindles in C57BL/6Jdy 2J/dy 2J dystrophic mice

Summary The sensory organs of skeletal muscles, the muscle spindles, were examined using electron microscopy indy ^2J/dy ^2J dystrophic mice. Despite widespread damage to the extrafusal (skeletomotor) fibres the intrafusal (spindle) fibres appeared normal and seemed resistant to the aetiological factors for murine dystrophy.This work was supported by grants from the Medical Research Council and the Science Research Council of Great Britain.     

Ultrastructure of muscle spindles in C57BL/6J dy2J/dy2J dystrophic mice.

The sensory organs of skeletal muscles, the muscle spindles, were examined using electron microscopy in dy2J/dy2J dystrophic mice. Despite widespread damage to the extrafusal (skeletomotor) fibres the intrafusal (spindle) fibres appeared normal and seemed resistant to the aetiological factors for murine dystrophy.     

Tricyclic antidepressants antagonize prostaglandin (PG) E20induced contractions of the guinea pig ileum and hypomotility in the mouse

Summary The interactions of PGE₂ and 2 tricyclic antidepressants were tested both on the guinea pig ileum and motility in the mouse. PGE₂-induced contractions of the guinea pig ileum were irreversibly blocked by amitriptyline and desipramine. Chronic administration of amitriptyline and desipramine blocked PGE₂-induced hypomotility in the mouse.     

Effects of pCai and pHi on cell-to-cell coupling

Summary Internal longitudinal resistance (r_i), a determinant of cardiac conduction, is affected by changes in intracellular calcium and protons. However, the role and mechanism by which H⁺ and Ca²⁺ may modulate r_i is uncertain. Cable analysis was performed in cardiac Purkinje fibers to measure r_i during various interventions. In some experiments, intracellular pH (pH_i) was recorded simultaneously to study the pH_i-r_i relation. Both intracellular Ca²⁺ and H⁺ independently modified r_i. However, internal resistance of cardiac fibers was insensitive to pH_i changes compared to other tissues. A latent period preceded the pH_i-related changes in r_i and the amount of change depended upon methodology. The results suggest that direct action of protons on r_i may be subordinate to other regulatory processes. Ionic regulation of internal longitudinal resistance may occur by more than one mechanism: i) direct cationic binding to sites on junctional membrane proteins; and ii) H⁺- or Ca²⁺-dependent phosphorylation of junctional proteins.     

The cyclic motor activity of the ovine gut: its reset at a faster rhythm

Summary In adult sheep, the frequency of the migrating motor complexes (MMC) was increased by the duodenal administration of methysergide, but not affected by other 5-HT₁ or 5-HT₂ antagonists. This reset of the MMC pattern at a faster rhythm suggests a selective action on the enteric neuronal serotoninergic mechanism modulating the pacing of the gut cyclic motor activity.     

Activation of the human FP prostanoid receptor disrupts mitosis progression and generates aneuploidy and polyploidy

Studies have shown prostaglandin F_2α to be an endogenous tumor promoter in mouse models of skin carcinogenesis; however, the mechanisms by which PGF_2α affects cell cycle events remain unknown. Here we performed cell cycle analyses on HEK cells stably expressing the human FP receptor and found that treatment with PGF_2α delays mitosis and is associated with an increased expression of cyclin B1 and Cdc2 kinase activity. In addition, multipolar spindles and misaligned chromosomes were observed in a significant proportion of cells treated with PGF_2α. Defective cytokinesis was also observed which resulted in gross aneuploidy and polyploidy. Expression of dominant negative Rho attenuated the cell cycle delay and prevented the generation of micronuclei following treatment with PGF_2α. This suggests that FP receptor activation of Rho signaling by PGF_2α can interfere with nuclear division. Aneuploidy is associated with genomic instability and may underlie the tumor-promoting properties of PGF_2α. Received 7 July 2005; received after revision 22 October 2005; accepted 11 November 2005     

Acid-base equilibrium in the blood of sheep

Summary The acid-base equilibrium in the blood of sheep is different from that of human blood mainly because of a lower concentration of 2,3-DPG. A nomogram relating pH, pCO₂, total CO₂ content and base excess has been developed.     

The elegans of spindle assembly

The Caenorhabditis elegans one-cell embryo is a powerful system in which to study microtubule organization because this large cell assembles both meiotic and mitotic spindles within the same cytoplasm over the course of 1 h in a stereotypical manner. The fertilized oocyte assembles two consecutive acentrosomal meiotic spindles that function to reduce the replicated maternal diploid set of chromosomes to a single-copy haploid set. The resulting maternal DNA then unites with the paternal DNA to form a zygotic diploid complement, around which a centrosome-based mitotic spindle forms. The early C. elegans embryo is amenable to live-cell imaging and electron tomography, permitting a detailed structural comparison of the meiotic and mitotic modes of spindle assembly.     

Isoprenaline-like effects of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine on mechanical,biochemical and electrophysiological parameters in the mammalian heart

Summary The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) mimicked the effects of isoprenaline on the force of contraction, the cAMP content and the slow Ca⁺⁺ inward current (I_si) in isolated guinea pig papillary muscles. The results support the hypothesis that phosphodiesterase inhibitors and -adrenoceptor agonists exert their positive inotropic effects by increasing I_si via the common mediator cAMP.Acknowledgment. This work was supported by the Deutsche Forschungsgemeinschaft.     

Expression of alpha-cardiac myosin heavy chain in mammalian skeletal muscle

We have investigated the reactivity of different human, rat and cat muscles to a monoclonal antibody directed against human -cardiac myosin heavy chain. We have found that special fiber subpopulations of human massetr and extraocular muscles, as well as the bag fibers of human, rat and cat muscle spindles, were reactive to this antibody, indicating that these fibers expressed -cardiac myosin heavy chain or a closely related isoform. This isomyosin was present in the spindle bag fibers at early fetal stages, whereas its expression in masseter and extraocular muscle fibers was not detected during the first 22 weeks of gestation. Our results add to the list of muscle proteins which are expressed in locations or at developmental stages other than those initially described, suggesting that a revision of the present nomenclature of the subgroups of myosin heavy chains might be considered in the future.     

A glucagon-secretin-like peptide stimulates the intrinsic nervous plexus of guinea pig gallbladder

Summary The role of vasoactive intestinal peptide (VIP), as a possible neurotransmitter of the intrinsic nerve plexus in the guinea pig gallbladder, was investigated by monitoring spontaneous contractile activity. VIP receptor antagonist (4 Cl-D-Phe⁶, Leu¹⁷)-VIP did not produce any effect on muscular tone and spontaneous activity, whereas (N-Ac-Tyr¹, D-Phe²)-GRF-(1-29)-NH₂, (14-GRF analog), which is known to stimulate digestive enzyme secretion by interacting with the VIP-preferring receptors, greatly increased the amplitude and frequency of waves as well as the muscular tone. Since VIP receptor antagonist acts selectively as a competitive antagonist for the action of VIP, we conclude that the gallbladder inhibitory intrinsic plexus neurotransmitter is not VIP, but a member of the glucagon-secretin family of peptides.     

Loss of antibody production accompanied by chromosome loss in a cloned hybrid line secreting antibodies to sheep red blood cells

Summary Somatic cell hybrids between Sp2/O-Ag14 mouse myeloma cells and lymphocytes derived from BALB/c mice hyperimmunized with sheep red blood cells (SRBC) were produced. One hybrid producing IgG₁ antibody to SRBC was selected, cloned twice and subsequently transferred to BALB/c mice. After a number of transfers it was found that the antibody titer in ascitec fluid gradually decreased. Cytogenetic analysis revealed gradual chromosome loss in the hybrid clone, which produced progressively less antibody.     

Tetrodotoxin slightly shortens action potential duration in ventricular but not in atrial heart muscle

Summary Tetrodotoxin (TTX), at concentrations significantly decreasing maximal upstroke velocity (dV/dt_max) of the action potential, exerted variable effects on action potential duration (APD) in different myocardial preparations. APD was virtually unchanged by tetrodotoxin in the guinea pig atrium, but slightly shortened in the guinea pig ventricle at maximally effective concentrations. In the human ventricle, both dV/dt_max and APD were reduced in the same concentration range of TTX. These results suggest that a TTX-sensitive sodium current significantly contributes to the repolarization phase of the action potential in ventricular but not in atrial heart muscle.Supported by the Deutsche Forschungsgemeinschaft (Na 105/5-5) and by the Fonds der Chemischen Industrie. Author to whom reprint requests should be addressed. We thank Mrs. Johanna Rupp for expert technical help. We also thank one referee for suggesting the experiments depicted in figure 4.     

Production of active and passive anaphylactic shock in the WBB6F1 mouse,a mast cell-deficient strain

Summary The role of mast cells in active and passive anaphylactic shock was examined using the WBB6F₁ mouse, a genetically mast cell-deficient strain. Lethal anaphylactic shock occurred at high incidence rates in mice actively sensitized to bovine serum albumin (BSA). The reaction was specific to BSA since the shock could not be elicited by human or guinea pig serum albumin in these animals. Lethal shock could be prevented by CV-3988 but not by cyproheptadine, which suggests that the shock is mediated by PAF but not by histamine and serotonin. Similarly, lethal shock was provoked by homologous antigens in mice which had been passively sensitized with allogeneic anti-benzylpenicilloyl (BPO) IgG₁ monoclonal antibody or with allogeneic or xenogeneic anti-BSA antiserum, but not in those sensitized with allogeneic anti-BPO IgE monoclonal antibody. These findings suggest that mast cells are not necessarily required for anaphylactic shock in the mouse.     

Mechanical and biochemical characterization of the contraction elicited by a calcium-independent myosin light chain kinase in chemically skinned smooth muscle

Summary The contraction induced by a Ca²⁺-independent myosin light chain kinase (MLCK-) was characterized in terms of isometric force (F_o), immediate elastic recoil (SE), unloaded shortening velocity (V_us), shortening under a constant load and ATPase activity of chemically skinned smooth muscle preparations. These parameters were compared to those measured in a Ca²⁺-induced contraction to assess the nature of cross bridge interaction in the MLCK-induced contraction. F_o developed in chicken gizzard fibers as well as SE were similar in contractions elicited by either agent. V_us in the contraction induced by MLCK-(0.36 mg/ml) was similar though averaged 39.3±8.9% less than V_us induced by Ca²⁺ (1.6x10^–6M) in the control fibers. Addition of Ca²⁺ (1.6x10^–6M) to a contraction induced by MLCK-resulted in small increases in both F_o and V_us. Shortening under a constant load was similar for both types of contractions. The contraction induced by MLCK-was accompanied by an increased rate of ATP hydrolysis. The MLCK-induced contraction is thus kinetically similar though not identical to a contraction induced by Ca²⁺. We conclude that with respect to actin-myosin interaction, MLCK- and Ca²⁺-induced contractions are similar.     

Mid-anaphase arrest in S. cerevisiae cells eliminated for the function of Cin8 and dynein

S. cerevisiae anaphase spindle elongation is accomplished by the overlapping function of dynein and the kinesin-5 motor proteins, Cin8 and Kip1. Cin8 and dynein are synthetically lethal, yet the arrest phenotypes of cells eliminated for their function had not been identified. We found that at a non-permissive temperature, dyn1Δ cells that carry a temperature-sensitive cin8 – 3 mutation arrest at mid-anaphase with a unique phenotype, which we named TAN (two microtubule asters in one nucleus). These cells enter anaphase, but fail to proceed through the slow phase of anaphase B. At a permissive temperature, dyn1Δ, cin8 – 3 or dyn1Δcin8 – 3 cells exhibit perturbed spindle midzone morphologies, with dyn1Δcin8 – 3 anaphase spindles also being profoundly bent and nonrigid. Sorbitol, which has been suggested to stabilize microtubules, corrects these defects and suppresses the TAN phenotype. We conclude that dynein and Cin8 cooperate in anaphase midzone organization and influence microtubule dynamics, thus enabling progression through the slow phase of anaphase B. Received 10 August 2008; received after revision 22 October 2008; accepted 27 October 2008     

Prostaglandin-like substances inPropionibacterium acnes. V. Activity profiles using cascade superfusion bioassay and platelet aggregation

Summary The activity spectrum of prostaglandin-like substances (PLS) fromP. acnes was investigated with cascade superfusion technique and by platelet aggregation assay. The biological activity of PLS resembles that of PGI₂: both relax bovine coronary artery, rabbit mesentric and coeliac arteries; both contract the rat stomach strip as well as both typically inhibit spontaneous movements of isolated guinea pig ileum. Also, similarly to PGI₂, PLS inhibits platelet aggregation regardless the inducer used. However, PLS possesses a specific antiaggregatory pattern on platelet, which indicates that these compounds are not indentical with primary prostaglandins or PGI₂.     

Purification and some properties of hemagglutinin from the Myxomycete,Physarum polycephalum

A new hemagglutinin was isolated from the plasmodium ofPhysarum polycephalum by salting out with ammonium sulphate followed by chromatography on DE-32, DEAE-Toyopearl and hydroxyapatite. This hemagglutinin, named physarumin, was purified 1000-fold over crude extracts. The molecular weight of physarumin was determined to be 22,000 by size exclusion chromatography on Bio-Gel P-60 and 8,700 by SDS-polyacrylamide gel electrophoresis. Physarumin agglutinated rabbit, guinea pig, horse and human erythrocytes. Physarumin-induced hemagglutination was inhibited by fetuin and ₁ glycoprotein, but not by commercially available mono-and disaccharides. Hemagglutinating activity was blocked by EDTA, and was restored by adding Ca²⁺ but not by Mg²⁺.