Sex difference in maximal oxygen uptake. Effect of equating haemoglobin concentration

Ten men and 11 women were studied to determine the effect of experimentally equating haemoglobin concentration ([Hb]) on the sex difference in maximal oxygen uptake (VO2max). VO2max was measured on a cycle ergometer using a continuous, load-incremented protocol. The men were studied under two conditions: 1) with normal [Hb] (153 g X L-1) and 2) two days following withdrawal of blood, which reduced their mean [Hb] to exactly equal the mean of the women (134 g X L-1). Prior to blood withdrawal, VO2max expressed in L X min-1 and relative to body weight and ride time on the cycle ergometer test were greater (p less than .01) in men by 1.11 L X min-1 (47%), 4.8 ml X kg-1 min-1 (11.5%) and 5.9 min (67%), respectively, whereas VO2max expressed relative to fat-free weight (FFW) was not significantly different. Equalizing [Hb] reduced (p less than .01) the mean VO2max of the men by 0.26 L X min-1 (7.5%), 3.2 ml X kg-1 min-1 (6.9%) or 4.1 ml X kg FFW-1 min-1 (7.7%), and ride time by 0.7 min (4.8%). Equalizing [Hb] reduced the sex difference for VO2max less than predicted from proportional changes in the oxygen content of the arterial blood and arteriovenous oxygen content difference during maximal exercise. It was concluded that the sex difference in [Hb] accounts for a significant, but relatively small portion of the sex difference in VO2max (L X min-1). Other factors such as the dimensions of the oxygen transport system and musculature are of greater importance.     

Operant behavior in transition reflects neonatal exposure to cadmium

Male Long-Evans rats were injected with 0, 1, 3, or 6 mg/kg of cadmium chloride on the first day of life. Animals free of morphological stigmata at weaning were selected for study. Tissue concentrations of cadmium and operant behavior under various fixed-ratio (FR) schedules of reinforcement were evaluated when these rats were adults. Dose-related increases in cadmium were present in the brains, livers, and kidneys. Dose-related differences in behavior were most evident during the transition from fixed ratio 25 (FR 25 or 25 responses/reinforcer) to FR 75. An inverted U describes the relationship between response output during the transition to FR 75 and cadmium chloride dose response output increased at 3 mg/kg and decreased at 6 mg/kg. The rate decreases were not correlated with weight loss that appeared after some of the animals exposed to 6 mg/kg reached 60 days of age. Challenge doses of d-amphetamine revealed no interaction between neonatal exposure to cadmium and d-amphetamine. The occurrence of alterations in operant behavior in animals that appeared normal on a number of preweaning evaluations suggests that operant behavior in transition was sensitive to subtle effects not observed with other commonly used tests. The data provide evidence for delayed effects in the adult that are due to neonatal exposure to cadmium.     

Inhibition of sarcoplasmic reticulum calcium pump by cytosolic protein(s) endogenous to heart and slow skeletal muscle but not fast skeletal muscle

Cytosol from rabbit heart and slow and fast skeletal muscles was fractionated using (NH₄)₂SO₄ to yield three cytosolic protein fractions, viz., CPF-I (protein precipitated at 30% saturation), CPF-II (protein precipitated between 30 and 60% saturation), and cytosol supernatant (protein soluble at 60% saturation). The protein fractions were dialysed and tested for their effects on ATP-dependent, oxalate-supported Ca²⁺ uptake by sarcoplasmic reticulum from heart and slow and fast skeletal muscles. CPF-I from heart and slow muscle, but not from fast muscle, caused marked inhibition (up to 95%) of Ca²⁺ uptake by sarcoplasmic reticulum from heart and from slow and fast muscles. Neither unfractionated cytosol nor CPF-II or cytosol supernatant from any of the muscles altered the Ca²⁺ uptake activity of sarcoplasmic reticulum. Studies on the characteristics of inhibition of sarcoplasmic reticulum Ca²⁺ uptake by CPF-I (from heart and slow muscle) revealed the following: (a) Inhibition was concentration- and temperature-dependent (50% inhibition with approx. 80 to 100 μg CPF-I; seen only at temperatures above 20°C). (b) The inhibitor reduced the velocity of Ca²⁺ uptake without appreciably influencing the apparent affinity of the transport system for Ca²⁺. (c) Inhibition was uncompetitive with respect to ATP. (d) Sarcoplasmic reticulum washed following exposure to CPF-I showed reduced rates of Ca²⁺ uptake, indicating that inhibition results from an interaction of the inhibitor with the sarcoplasmic reticulum membrane. (e) Concomitant with the inhibition of Ca²⁺ uptake, CPF-I also inhibited the Ca²⁺-ATPase activity of sarcoplasmic reticulum. (f) Heat-treatment of CPF-I led to loss of inhibitor activity, whereas exposure to trypsin appeared to enhance its inhibitory effect. (g) Addition of CPF-I to Ca²⁺-preloaded sarcoplasmic reticulum vesicles did not promote Ca²⁺ release from the vesicles. These results demonstrate the presence of a soluble protein inhibitor of sarcoplasmic reticulum Ca²⁺ pump in heart and slow skeletal muscle but not in fast skeletal muscle. The characteristics of the inhibitor and its apparently selective distribution suggest a potentially important role for it in the in vivo regulation of sarcoplasmic reticulum Ca²⁺ pump, and therefore in determining the duration of Ca²⁺ signal in slow-contracting muscle fibers.     

The central connections and actions during walking of tibial campaniform sensilla in the locust

Strain acting on the exoskeleton of insects is monitored by campaniform sensilla. On the tibia of a mesothoracic leg of the locust (Schistocerca gregaria) there are three groups of campaniform sensilla on the proximo-dorsal surface. This study analyses the responses of the afferents from one group, their connections with central neurones and their actions during walking.The afferents of the campaniform sensilla make direct excitatory connections with flexor tibiae motor neurones. They also make direct connections with particular spiking local interneurones that make direct inhibitory output connections with the slow extensor tibiae motor neurone.During walking extension movements of the tibiae during stance produce longitudinal tensile forces on the dorsal tibia that peak during mid stance before returning to zero prior to swing. This decline in tension can activate the campaniform sensilla. In turn this would lead to an inhibition of the extensor tibiae motor neurone and an excitation of the flexor tibiae motor neurones. This, therefore, aids the transition from stance to swing. During turning movements, the tibia is flexed and the dorsal surface is put under compression. This can also activate some of campaniform sensilla whose effect on the flexor motor neurones will reinforce the flexion of the tibia.     

Bax conformational change is a crucial step for PUMA-mediated apoptosis in human leukemia

The BH3-only protein, PUMA, plays an important role in p53-mediated apoptosis. The apoptotic effect of PUMA on the mitochondria was studied using a p53-negative, human leukemia K562 cell line. Overexpression of PUMA was accompanied by an increased Bax expression, Bax conformational change, and translocation to mitochondria. A PUMA-BH3 peptide can induce Bax conformational change, cytochrome c release, and reduction in the mitochondrial membrane potential (DeltaPsi(m)) in isolated K562 mitochondria and can be inhibited by Bcl-XL. The homo-dimer of Bax/Bax was also weakly shown after mitochondria were treated with PUMA-BH3 peptide but may not be lethal for PUMA-induced apoptosis in K562 cells. Our results suggest that PUMA-induced Bax conformational change and Bax translocation to mitochondria can be separate events and the conformational change in Bax is crucial for PUMA-induced mitochondrial dysfunction.     

Potential mechanisms of leukemia cell resistance to TRAIL-induced apopotosis

There are many factors contributing to the resistance to TRAIL (Tumor necrosis factor-related apoptosis-inducing ligand)-induced apoptosis. However, it is not clear whether the mechanism of resistance to TRAIL is constitutive or inductive. Therefore, the purpose of this study was to investigate the resistant mechanisms to TRAIL at different levels in the apoptotic pathway. The human T-lymphoblastic leukemic CEM cell line showed more resistant to TRAIL-induced apoptosis compared with the human chronic myeloid leukemic K562 cell line. Lower level of constitutive caspase-8 expression in the CEM cell line led to a poor response to both TRAIL-induced activation of caspase-3 and reduction in the mitochondrial membrane potential (m). There was no significant difference in the constitutive levels of NF-B in CEM and K562 cell lines. However, CEM cells showed a faster response to TRAIL-induced NF-B activation than K562 cells. TRAIL-induced regulation of Bcl-2 family of proteins included an up-regulation in Bcl-2/Bcl-XL and a down-regulation in Bax. IAPs, such as XIAP, cIAP-1, cIAP-2 and Survivin were all up-regulated during the treatment with TRAIL. In summary, our data suggest that the leukemic cells resistance to TRAIL-induced apoptosis might be due to the deficiency in the constitutive caspase-8 expression. Development of potential resistance to apoptosis by TRAIL can occur in both TRAIL-resistant and TRAIL-sensitive leukemic cells.     

Distribution of NADPH-diaphorase-positive ascending interneurones in the crayfish terminal abdominal ganglion

Previous neuropharmacological studies have described the presence of a nitric oxide-cGMP signalling pathway in the crayfish abdominal nervous system. In this study we have analysed the distribution of putative nitric oxide synthase (NOS)-containing ascending interneurones in the crayfish terminal abdominal ganglion using NADPH-diaphorase (NADPHd) histochemistry. Ascending intersegmental interneurones were stained intracellularly using the fluorescent dye Lucifer yellow and the ganglia containing the stained interneurones subsequently processed for NADPHd activity. Fluorescence persisted throughout histochemical processing. These double-labelling experiments showed that 12 of 18 identified ascending interneurones were NADPHd positive. Thus many ascending interneurones that process mechanosensory signals in the terminal ganglion may contain NOS, and are themselves likely sources of NO which is known to modulate their synaptic inputs. Three clear relationships emerged from our analysis between the effects of NO on the synaptic inputs of interneurones, their output properties and their staining for NADPH-diaphorase. First were class 1 interneurones with no local outputs in the terminal ganglion, the NE type interneurones, which had sensory inputs that were enhanced by NO and were NADPHd positive. Second were class 1 interneurones with local and intersegmental output effects that had sensory inputs that were also enhanced by NO but were NADPHd negative. Third were class 2 interneurones with local and intersegmental outputs that had synaptic inputs that were depressed by the action of NO but were NADPHd positive. These results suggest that NO could selectively enhance specific synaptic connections and sensory processing pathways in local circuits.     

Cell death in leukemia: passenger protein regulation by topoisomerase inhibitors

Etoposide is a potent inducer of mitotic catastrophe; a type of cell death resulting from aberrant mitosis. It is important in p53 negative cells where p53 dependent apoptosis and events at the G1 and G2 cell cycle checkpoints are compromised. Passenger proteins regulate many aspects of mitosis and siRNA interference or direct inhibition of Aurora B kinase results in mitotic catastrophe. However, there is little available data of clinical relevance in leukaemia models. Here, in p53 negative K562 myeloid leukemia cells, etoposide-induced mitotic catastrophe is shown to be time and/or concentration dependent. Survivin and Aurora remained bound to chromosomes. Survivin and Aurora were also associated with Cdk1 and were shown to form complexes, which in pull down experiments, included INCENP. There was no evidence of Aurora B kinase suppression. These data suggests etoposide will complement Aurora B kinase inhibitors currently in clinical trials for cancer.