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.     

The generation of new ‘white’ muscle fibers by budding in the lateral musculature of elversAnguilla anguilla (L.) during normal development

Summary The elver is a developmental stage of the European eel Anguilla anguilla (L.). During its growth, relatively large numbers of new muscle fibers are formed in the lateral musculature. We investigated the origin of these fibers. They proved to originate from already existing fibers by budding.     

The significance of temperature and barometric pressure changes for the snow surface activity ofIsotoma hiemalis (Collembola)

Summary Temperature is limiting for the snow surface activity ofIsotoma hiemalis: values below a threshold of –2.5° to –3°C are avoided. Changing barometric pressure leads to increased surface activity, thus being responsible for mass appearances. These experiments provide the first evidence for sensitivity to and reaction to barometric pressure changes in insects.The financial support by the Swiss National Science Foundation is highly acknowledged. I thank W. Matthey for the unpublished data onGerris remigis.     

Juvenile hormone and reproduction in the cricket. II. Effect of rearing temperature on corpus allatum activity (in vitro) in adult females

Summary In the Mediterranean field cricket,Gryllus bimaculatus, reproduction is controlled by temperature and the corpus allatum (CA) hormone JH III. In CA of females reared at 24°12°C(168 h) (high reproduction rate) a first peak in JH III synthesis is reached about 4 days earlier than in those of 20°C females (low reproduction rate). Furthermore, in 20°C animals CA activity is low during the entire oviposition period, whereas at 24°12°C high CA activity is found during this period of adult life. The results indicate a stimulation of CA activity and reproduction by thermoperiods around a constant low temperature.Supported by the DFG (SFB 87 A 4).     

Interaction between the effects of centrally administered arecoline and leucocyte pyrogen on the activity of posterior hypothalamic neurons in the rabbit

Summary In experiments with urethane-anesthetized rabbits, the alteration in the activity of posterior hypothalamic neurons resulting from intracerebroventricular injection of leucocyte pyrogen was attentuated by subsequent administration of arecoline. Atropine failed to alter the neuronal response to leucocyte pyrogen but abolished the effect of arecoline. The neuronal response to arecoline was reversed in the absence of leucocyte pyrogen.     

Afferent fibers from the septum terminate on gamma-aminobutyric acid (GABA-) interneurons and granule cells in the area dentata of the rat

Summary Interneurons in the area dentata of the rat were immunostained with an antibody to gamma-aminobutyric acid. After septal lesions, degenerating terminals were found in asymmetric synaptic contact with granule cell somata and dendritic elements of immunoreactive and nonreactive cells in the supragranular part of the molecular layer.     

Afferent fibers from the septum terminate on gamma-aminobutyric acid (GABA-) interneurons and granule cells in the area dentata of the rat

Interneurons in the area dentata of the rat were immunostained with an antibody to gamma-aminobutyric acid. After septal lesions, degenerating terminals were found in asymmetric synaptic contact with granule cell somata and dendritic elements of immunoreactive and nonreactive cells in the supragranular part of the molecular layer.     

The effects of thermogenic agents on hindlimb oxygen consumption in the dog: ICI D7114 and noradrenaline

The thermogenic action of beta-adrenoceptor agonists may be due, in part, to increased metabolism in skeletal muscle. Previous results suggest that vasoconstriction is also necessary, and that the effect can be blocked by vasodilators. Both noradrenaline and the beta-3 agonist, ICI D7114, were studied using two dog hindlimb protocols. During constant perfusion conditions, ICI D7114 caused a significant increase in hindlimb oxygen consumption although it is a vasodilator. Noradrenaline resulted in a smaller rise in oxygen consumption, and produced a marked vasoconstriction. Both noradrenaline and ICI D7114 resulted in decreased oxygen consumption when the blood flow was allowed to vary in response to the drug treatment. The results suggest that changes in tissue oxygen consumption caused by beta-agonists are not related to vasomotion.     

The effects in vivo of some sex hormones on the growth of tibias of normal and chondrodystrophic (Creeper) chick embryos]

Various sex hormones (testosterone, oestradiol, dehydroepiandrosterone), in the form of suspensions in oil, are injected into the allantois of normal and chondrodystrophic (Creeper) chick embryos of 6 days 1/2 incubation. Observations made on each of the phenotypes on the 12th day of incubation show that oil injected alone causes a significant decrease in the dry weight of the tibiae. This inhibitory effect is partially abolished when the oil is injected together with the sex hormones, testosterone being the most effective.     

Decreased rates of Ca2+-dependent heat production in slow- and fast-twitch muscles from the dystrophic (mdx) mouse

Using a newly developed microcalorimetric approach to assess the rate of energy expenditure for intracellular [Ca²⁺] homeostasis in isolated muscles at rest, we found this was lower inmdx than in control mouse muscles, by 62% and 29% in soleus and extensor digitorum longus, respectively. Differences in total and Ca²⁺-dependent rates of specific heat production betweenmdx and control were enhanced during sustained, KCl-induced stimulation of energy dissipation. These results suggest that the low sacroplasmic energy status of dystrophic muscles is not due to any excessive energy expenditure for intracellular [Ca²⁺] homeostasis.     

The effects of diverse agents (Ca++ and K++ ionophores, organomercurials, dithiols, colchicine, and cytochalasin B) on the maturation and differentiation without cleavage in Chaetopterus eggs]

Induction of maturation in Chaetopterus oocytes requires the presence of Ca++ ions in the medium, but differentiation without cleavage can proceed in the absence of this cation. The Ca++ ionophore A 23187 induces both maturation and the cortical reaction provided that Ca++ ions are present in the medium differentiation without cleavage may follow. Valinomycin slowly induces germinal vesicle breakdown, which is followed by a sharp segregation between hyaloplasm and yolk. PHMPS, but not DTT, induces maturation. Differentiation without cleavage is more sensitive to colchicin than to cytochalasin B.