Changes in active uptake of noradrenalin-14C by rat brain synaptosomes during conditioning

Active uptake of noradrenalin-¹⁴C (NA-¹⁴C) by rat brain synaptosomes was shown to be inhibited by the action of ouabain (0.1 M) and during potassium depolarization. Defensive conditioning (DC) led to depression of active uptake of NA by synaptosomes. This effect may be connected both with changes in the state of the presynaptic membranes and with possible enhancement of the function of postsynaptic adrenergic receptors.Laboratory of Neurochemical Mechanisms of Conditioned Reflexes, Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR. Laboratory of General Pathology of the Nervous System, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 87, No. 2, pp. 137–139, February, 1979.     

The relationship between 67Ga accumulation and ATP metabolism in tumor cells in vitro

Previously, we reported that the deposition of ⁶⁷Ga into malignant tumors may be a sensitive index of proliferative activity in tumor cells. For the purpose of elucidation of this hypothesis, we investigated the relationship between the accumulation of ⁶⁷Ga into malignant tumor cells and the intra cellular ATP metabolism in vitro.The uptake of ⁶⁷Ga into tumor cells was inhibited by adding NaF which is an inhibitor of ATP production. Furthermore, the uptake of ⁶⁷Ga into tumor cells was strongly inhibited by adding ouabain which is a specific inhibitor of Na⁺–K⁺-ATPase. From these in vitro results, it was concluded that there is a correlation between ⁶⁷Ga uptake and intra cellular ATP metabolism in tumor cells.     

Characterization of [H]hemicholinium-3 binding associated with neuronal choline uptake sites in rat brain membranes

Hemicholinium-3 (HCh-3) is a potent and specific inhibitor of the high-affinity choline transport process (HAChT) localized on cholinergic neurons. In this study, the specific binding of [³H]HCh-3 (120 Ci/mmol) was characterized in crude synaptic membranes prepared from rat brain. The binding of [³H]HCh-3 to forebrain membranes was saturable, reversible and specific with an apparent K_d under optimal conditions of 35 nM and a B_max of 56 fmol/mg protein. The potency of various HAChT inhibitors correlated with their apparent affinities for the specific [³H]HCh-3 binding site. The specific binding of [³H]HCh-3 exhibited an uneven regional distribution in the adult rat brain that corresponded to the activity of the HAChT in these regions. Transsection of the fornix, which causes a degeneration of the septal hippocampal cholinergic pathway, resulted in comparable reductions of the specific [³H]HCh-3 binding and the specific activity of choline acetyltransferase, a presynaptic marker for cholinergic terminals in the hippocampal formation; the lesion did not affect the specific activity of glutamic acid decar☐ylase, a presynaptic marker for GABAergic neurons within the hippocampus. Maximal binding occurred in the presence of 200 mM NaCl: potassium, lithium, rubidium and calcium substituted poorly for sodium; and bromide, fluoride, iodide, sulfate and phosphate were less effective anions than chloride. Increasing concentrations of NaCl increased the affinity of the site for [³H]HCh-3 with no significant effect on the maximal number of sites; the enhancement of affinity was due to a selective slowing of the rate of dissociation of the ligand from its binding site. These findings indicate that [³H]HCh-3 binds to the carrier site mediating the HAChT on cholinergic neurons; thus, this radioligand may be a useful probe for investigating this presynaptic component (HAChT) of cholinergic neurons.     

The relationship between Ga-67 accumulation and cell cycle in malignant tumor cells in vitro

Previously we reported that the deposition of ⁶⁷Ga into malignant tumor may be a sensitive index of proliferative activity in tumor cells. For the purpose of elucidation of this hypothesis, we investigated the relationship between the accumulation of ⁶⁷Ga into malignant tumor cells and the cell cycle in vitro. We discovered that the uptake of both ⁶⁷Ga and ⁵⁹Fe into synchronized mouse tumor cells reaches a peak at the G2 stage which precedes cellular proliferation. Both iron and transferrin are specifically required by cells in culture for cell division, and the fact that ⁶⁷Ga and ⁵⁹Fe uptake into tumor cells peaks at the G2 stage of the cell cycle suggests that there is a correlation between ⁶⁷Ga uptake and the rate of cellular proliferation in malignant tumor cells.     

Cellular Uptake Mechanism of Amino Acid Ester Prodrugs in Caco-2/hPEPT1 Cells Overexpressing a Human Peptide Transporter

Purpose. This study characterized the cellular uptake mechanism and hydrolysis of the amino acid ester prodrugs of nucleoside antiviral drugs in the transiently transfected Caco-2 cells overexpressing a human intestinal peptide transporter, hPEPTl (Caco-2/hPEPTl cells). Methods. Amino acid ester prodrugs of acyclovir and AZT were synthesized and their apical membrane permeability and hydrolysis were evaluated in Caco-2/hPEPTl cells. The cellular uptake mechanism of prodrugs was investigated through the competitive inhibition study in Caco-2/hPEPTl cells. Results. L-Valyl ester of acyclovir (L-Val-ACV) was approximately ten fold more permeable across the apical membrane than acyclovir and four times more permeable than D-valyl ester of acyclovir (D-Val-ACV). Correspondingly, L-valyl ester of AZT (L- Val-AZT) exhibited three fold higher cellular uptake than AZT. Therefore, amino acid ester prodrugs significantly increased the cellular uptake of the parent drugs and exhibited the D,L-stereoselectivity. Furthermore, prodrugs were rapidly hydrolyzed to the parent drugs by the intracellular hydrolysis, following the apical membrane transport. In the inhibition studies, cephalexin and small dipeptides strongly inhibited the cellular uptake of L-Val-ACV while L-valine had no effect, indicating that the peptide transporter is primarily responsible for the apical membrane transport of L-Val-ACV. In addition, the cellular uptake of L-Val-ACV was five times higher in Caco-2/hPEPT 1 cells than the uptake in the untransfected Caco-2 cells, implying the cellular uptake of L-Val-ACV was related to the enhancement of the peptide transport activity in Caco-2/hPEPTl cells. Conclusions. Caco-2/hPEPTl system is an efficient in vitro model for the uptake study of peptidyl derivatives. Amino acid ester prodrugs significantly improved the cellular uptake of the parent drugs via peptide transport mechanism and were rapidly converted to the active parent drugs by the intracellular hydrolysis.     

The motor unit potential distribution over the skin surface and its use in estimating the motor unit location

The amplitude of a surface electromyogram is dependent on the number of active motor units, their size and the relative position of the recording electrode. It is not possible to interpret the surface electromyogram quantitatively without disentangling these different aspects. In this study the decline of different components of the motor unit potential with increasing radial distance from the motor unit is quantified. Fifty-two motor units in the biceps brachii muscle were studied using 36-channel surface electromyography combined with intramuscular scanning electromyography. Scanning electromyography was used to locate precisely the motor unit. The dependence of the surface motor unit potential magnitude on the radial distance between the motor unit and the recording electrodes can be described fairly well by an inverse power function. The steepness of this function depends on the chosen motor unit potential parameter and the interelectrode distance, but also varies between motor units. The change of the negative peak amplitude of the motor unit potential over the skin surface can be used to give a fairly accurate estimate of the location of the motor unit under the skin surface. We found that for all practical purposes the depth of a motor unit in the biceps brachii muscle can be estimated as 20% of the distance over the skin surface where motor unit potentials can be recorded with higher amplitudes than 50% of the maximal amplitude recorded at the skin surface caused by activity of the same motor unit.     

Sensitivity to oxidants of mitochondrial and sarcoplasmic reticular calcium uptake in saponin-treated cardiac myocytes

Summary Calcium transport functions of mitochondria and sarcoplasmic reticulum (SR) were studied without prior extraction using isolated rat heart myocytes permeabilized with saponin. Calcium uptake by SR was rapid and its affinity was high in comparison to calcium uptake by mitochondria, which had a higher capacity. The sensitivity of uptake to two oxidants, H₂O₂ and HOCl (hypochlorous acid), depended on the cytosolic calcium concentration; when this was similar to the concentration in diastole (180 nM), HOCl inhibited calcium uptake by mitochondria and SR, whereas when the calcium concentration was 750 nM, mitochondrial calcium uptake showed relatively high resistance, although SR uptake was still markedly inhibited by HOCl. Calcium uptake of both mitochondria and SR was less sensitive to the action of H₂O₂ than to HOCl, and the H₂O₂ effect was less dependent on the cytosolic calcium concentration. Therefore, HOCl, when produced by activated leukocytes and supplied to the heart cells, may seriously impair the excitation-contraction coupling function of SR, whereas H₂O₂, possibly generated directly by mitochondria or generated from superoxide anions, may be tolerated relatively well by heart SR and mitochondria.Preliminary accounts of this work were presented as FASEB 1988. Dr. Kaminishi was a Canadian Heart Foundation Post-Doctoral fellow; his present address is Yamagata University, Japan.     

Effect of age and dietary protein level on ovine nitrogen metabolism—I. Evidence of comparable metabolizable nitrogen availability

Seven 8-month old and seven 9-yr old ewes were utilized to study the effects of age and dietary protein level on nitrogen and organic matter digestibilities and urinary and plasma nitrogenous constituents. Animals were fed individual maintenance levels, based on metabolic body size (W^0.75), of a diet containing 10% crude protein in trial 1 and isocaloric amounts of a diet containing 20% crude protein in trial 2. No age-related differences occurred in either trial for apparent digestible nitrogen (ADN) or organic matter. Nitrogen retention (g/kg W^0.75/day) was 0.09 ± 0.02 and 0.10 ± 0.01 in trial 1 and 0.09 ± 0.03 and 0.14 ± 0.03 in trial 2 for young and old ewes, respectively. Total urinary N as a percentage of ADN did not differ by age in either trial, and the relative proportions of urinary urea, ammonia-N and creatinine-N were comparable. Plasma urea and ammonia nitrogen were also similar for the two age groups in both trials. Asparagine, alanine, valine, leucine and total branched chain amino acids were significantly higher while arginine was lower in the plasma of young ewes in trial 1. In trial 2, glutamine, citrulline and arginine were significantly lower in the plasma of young ewes. Concentrations of essential, nonessential, branched and total amino acids were negatively correlated with protein retention in trial 1, while no significant correlations were observed in trial 2. These data suggest that in ewes of different ages fed at maintenance, availability of metabolizable nitrogen is comparable as indicated by no significant differences observed in digestion, absorption or excretion of nitrogen-containing metabolites measured in these studies. Thus, the differences seen in various plasma parameters reflect differences in metabolic processes due to age.     

Calcium uptake by myometrial membranes: Effect of A 23187, a calcium ionophore

A subcellular fraction, relatively enriched with plasma membranes, showed an ATP-dependent Ca²⁺ uptake. The addition of a Ca²⁺ ionophore, A 23187, greatly reduced the steady-state uptake of Ca²⁺ and also led to release of previously accumulated Ca²⁺. Other drugs (angiotensin, prostaglandin F₂, 5-hydroxytryptamine and cyclic nucleotides) had negligible effects on Ca²⁺ transport. The preparation appears to transport Ca²⁺, although binding is negligible.     

LONG-TERM EFFECT OF PREVIOUS SWIMTRAINING IN GIRLS. A 10-YEAR FOLLOW-UP OF THE "GIRL SWIMMERS"

ABSTRACT. Thirty girls, studied in 1961 after 2.5 years of intensive swimtraining, were the subject of a follow-up for ten years. When last examined, seven and ten years after the original study, all the girls had given up swimtraining. The increased values for vital capacity observed in 1961 remained unchanged, but residual volume, functional residual capacity and total lung capacity showed small increases even after corrections for body growth. Such increases are, however, normal in these years. Heart volume which was high originally, was found to be lower ten years later, although mean values were still higher than normal. The decrease seen from 1961 to 1971 could mainly be ascribed to a decrease in the subjects with the largest hearts originally. Both total hemoglobin and blood volume decreased to normal values in relation to body size. Maximal oxygen uptake, though, fell from 2.80 1/min (51.4 ml/kg × min) to 2.18 1/min (36.4 ml/kg × min) ten years later. It is suggested that the functional capacity of the cardiovascular system declined more markedly than its dimensions.