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Biomedical subjects

H Schulman

Publications and source records attributed to H Schulman.

At least 91 records · Page 5Linked to original sources
PubMed1993

Doppler velocimetry, placental morphology and outcome in insulin-dependent diabetes.

The purpose of this study was to determine the underlying cause of abnormal umbilical artery Doppler velocimetry in pregnancies complicated by insulin-dependent diabetes, by evaluating placental morphology and correlating Doppler results with pregnancy outcome. Our study population consisted of 14 pregnancies with normal Doppler results and 11 pregnancies with abnormal Doppler results. Quantitative placental examinations were performed. Maternal and perinatal characteristics were analyzed. Infants from the abnormal Doppler group had a statistically significantly higher incidence than those from the normal Doppler group of hyperbilirubinemia, Cesarean delivery for fetal distress, and neonatal intensive care stay of 2 or more days. Women with abnormal Doppler results delivered earlier (36 vs. 38 weeks) and had infants of lower birth weight (3079 vs. 3629 g). They were also three times more likely to have poor glycemic control (relative risk = 3.2; p = 0.0067). The placentae of both groups showed no statistically significant differences in placental weight, number of tertiary stem villi, number of small muscular arteries, or mean arterial width. Our findings suggest a functional rather than structural placental process as the cause of the abnormal Doppler results in pregnancies complicated by diabetes. An association between glycemic control and Doppler velocimetry is suggested.

Journal Article↗
PubMed1993

Cloning and analysis of two new isoforms of multifunctional Ca2+/calmodulin-dependent protein kinase. Expression in multiple human tissues.

Multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) is a mediator of calcium signals in diverse signaling pathways. In human lymphocytes and epithelial tissues, CaM kinase activates a chloride channel via a Ca(2+)-dependent pathway which is preserved in cystic fibrosis. To characterize the CaM kinase present in these tissues we have cloned an isoform of this kinase from human T lymphocytes. We show the cDNA structure of two variants of this human CaM kinase, gamma B and gamma C, which are predicted to translate to 518 and 495 amino acids, respectively. Amino acid differences between these isoforms and the rat brain gamma isoform (which we refer to as gamma A) are localized to the variable domain. We used RNase protection of this variable region to reveal the level of expression of gamma B and gamma C CaM kinase mRNAs in nine human tissues and cell lines. When transfected into Jurkat T cells, the gamma B cDNA encoded a functional kinase which cosedimented on sucrose gradients with endogenous T cell CaM kinase activity and formed a large multimeric enzyme. The recombinant gamma B isoform displayed two phases of autophosphorylation characteristic of CaM kinases, including the phase which converts it to a partially Ca(2+)-independent species. Site-directed mutagenesis of the predicted autoinhibitory domain yielded a mutant which was approximately 37% active in the absence of Ca2+/calmodulin, confirming the region as critical for autoregulation, and suggesting this mutant as a tool for studying the role of CaM kinase in nonneuronal tissues.

Amino Acid Sequence↗
PubMed1993

Multifunctional Ca2+/calmodulin-dependent protein kinase.

Multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) is a prominent mediator of neurotransmitters which elevate Ca2+. It coordinates cellular responses to external stimuli by phosphorylating proteins involved in neurotransmitter synthesis, neurotransmitter release, carbohydrate metabolism, ion flux and neuronal plasticity. Structure/function studies of CaM kinase have provided insights into how it decodes Ca2+ signals. The kinase is kept relatively inactive in its basal state by the presence of an autoinhibitory domain. Binding of Ca2+/calmodulin eliminates this inhibitory constraint and allows the kinase to phosphorylate its substrates, as well as itself. This autophosphorylation significantly slows dissociation of calmodulin, thereby trapping calmodulin even when Ca2+ levels are subthreshold. The kinase may respond particularly well to multiple Ca2+ spikes since trapping may enable a spike frequency-dependent recruitment of calmodulin with each successive Ca2+ spike leading to increased activation of the kinase. Once calmodulin dissociates, CaM kinase remains partially active until it is dephosphorylated, providing for an additional period in which its response to brief Ca2+ transients is potentiated.

Animals↗
PubMed1993

The multifunctional Ca2+/calmodulin-dependent protein kinases.

Ca2+ mediates the effect of many hormones, neurotransmitters and growth factors on contractility and motility, carbohydrate metabolism, cell cycle, gene expression and neuronal plasticity. Multifunctional Ca2+/calmodulin-dependent (CaM) kinase, CaM kinase Ia, CaM kinase Ib and CaM kinase IV are four of the kinases that mediate Ca(2+)-signaling pathways. Recent studies have clarified our understanding of their structure, regulation and function.

Amino Acid Sequence↗
PubMed1993

Endometrial and myometrial thickness and uterine blood flow in postmenopausal women: the influence of hormonal replacement therapy and age.

The aim of our study was to assess the age and hormonal influence on endometrial and myometrial thickness and uterine blood flow in postmenopausal women. One hundred and nine healthy postmenopausal women were examined by transvaginal ultrasonography and color Doppler ultrasonography. Twenty women (18.4%) were under continuous HRT for at least 1 year. In all patients, full thickness of the endometrium and half thickness of the myometrium was measured. Pulsed Doppler waveforms were used to calculate the RI for the left and right uterine arteries. Endometrium thickness in the groups without HRT did not change as the years of postmenopause progressed. This was also true for myometrial thickness. The resistance to blood flow in the uterine arteries remained the same as the postmenopause progressed, but with each 5 year analysis, the ability to see the uterine arteries decreased. The duration of the therapy did not affect the measured parameters. The thickness of the endometrium was larger in the groups with HRT in comparison with all groups without HRT (P < 0.01). Myometrial thickness and uterine blood flow are not affected and did not show any significant influence from HRT. In conclusion, continuous HRT significantly influences the thickness of the postmenopausal endometrium but not of the myometrium or the uterine artery blood flow.

Aged↗
PubMed1993

Cyclophosphamide cardiac injury mimicking acute myocardial infarction.

We report a patient in whom cyclophosphamide (CY) caused damage to the heart that was manifested by ST segment elevation and marked elevation of serum cardiac isoenzymes and mimicked myocardial infarction. Post-mortem examination did not reveal any local vascular event (e.g. thrombus or spasm) and suggested diffuse myocardial injury secondary to CY.

Adult↗
PubMed1992

Inhibitory autophosphorylation of multifunctional Ca2+/calmodulin-dependent protein kinase analyzed by site-directed mutagenesis.

Initial autophosphorylation of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) occurs at Thr286 (the "autonomy" site) and converts the kinase from a Ca(2+)-dependent to a partially Ca(2+)-independent or autonomous enzyme. After removal of Ca2+/calmodulin, the autonomous kinase undergoes a "burst" of inhibitory autophosphorylation at sites distinct from the autonomy site which may be masked in the presence of bound calmodulin. This burst of Ca(2+)-independent autophosphorylation blocks the ability of calmodulin to activate the kinase. We have used site-directed mutagenesis to replace putative inhibitory autophosphorylation sites within the calmodulin binding domain of recombinant alpha-CaM kinase with nonphosphorylatable alanines and examined the effects on autophosphorylation, kinase activity, and calmodulin binding. Although prominent Ca(2+)-independent autophosphorylation occurs within the calmodulin binding domain at Thr305, Thr306, and Ser314 in wild-type alpha-CaM kinase, the inhibitory effect on kinase activity and calmodulin binding is retained in mutants lacking any one of these three sites. However, when both Thr305 and Thr306 are converted to alanines the kinase does not display inhibition of either activity or calmodulin binding. Autophosphorylation at either Thr305 or Thr306 is therefore sufficient to block both binding and activation of the kinase by Ca2+/calmodulin. Thr306 is also slowly autophosphorylated in a basal reaction in the continuous absence of Ca2+/calmodulin. Autophosphorylation of Thr306 by the kinase in either its basal or autonomous state suggests that in the absence of bound calmodulin, the region of the autoregulatory domain surrounding Thr306, rather than the region near the autonomy site, lies nearest the peptide substrate binding site of the kinase.

Amino Acid Sequence↗
PubMed1992

Antisense oligodeoxynucleotides to the cystic fibrosis transmembrane conductance regulator inhibit cAMP-activated but not calcium-activated chloride currents.

Phosphorylation of the cystic fibrosis transmembrane conductance regulator (CFTR) by cAMP-dependent protein kinase leads to chloride flux in epithelial cells. Is CFTR also required for the calcium-dependent activation of chloride channels? We used antisense oligodeoxynucleotides to CFTR to reduce the expression of CFTR in colonic and tracheal epithelial cells. The antisense oligomers were a pair of adjacent 18-mers complementary to nucleotides 1-18 and 19-36 of CFTR mRNA. Sense and misantisense oligomers served as controls. A 48-h antisense treatment reduced the expression of CFTR protein as assayed by immunoprecipitation and autoradiography to 26% of the level in sense-treated T84 cells. Whole-cell patch clamp revealed that a 48-h antisense treatment of T84 and 56FHTE-8o- fetal tracheal epithelial cells reduced the cAMP-activated chloride current to approximately 10% of that in sense-treated cells. The half-life of functional CFTR is less than 24 h in these cells. In contrast, the calcium-activated chloride current was not affected by antisense treatment. Hence, the cAMP and calcium pathways are separate. CFTR is required for the cAMP pathway but not for the calcium pathway.

Base Sequence↗
PubMed1992

Multiple Ca2+ signaling pathways converge on CaM kinase in PC12 cells.

The role of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) in mediating various Ca2+ signaling pathways was examined in PC12 cells. Conversion of the kinase to a Ca(2+)-independent form was used to monitor which neurotransmitters activate the enzyme in situ. CaM kinase responds to Ca2+ influx elicited by ligand-gated Ca2+ channels for ATP and acetylcholine. It also responds to Ca2+ mobilization of IP3-sensitive stores elicited by phospholipase C-linked receptors for ATP and acetylcholine as well as by caffeine. CaM kinase mediates the actions of many neurotransmitters and Ca2+ signaling pathways.

Acetylcholine↗
PubMed1992

Cross-talk between protein kinase C and multifunctional Ca2+/calmodulin-dependent protein kinase.

Protein kinase C (PKC) exhibits both negative and positive cross-talk with multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) in PC12 cells. PKC effects negative cross-talk by inhibiting the mobilization of intracellular Ca2+ stores and by inhibiting Ca2+ influx through voltage-sensitive Ca2+ channels. In the absence of cross-talk, Ca2+ influx induced by depolarization with 56 mM K+ stimulates CaM kinase and its autophosphorylation and converts up to 50% of the enzyme to a Ca(2+)-independent or autonomous species. Acute treatment with phorbol myristate acetate (PMA) elicits a parallel reduction in depolarization-induced Ca2+ influx and in generation of autonomous CaM kinase. Negative cross-talk also occurs during stimulation of the phosphatidylinositol signaling system with bradykinin, which activates both PKC and CaM kinase. The extent of CaM kinase activation is attenuated by the simultaneous activation of PKC; it is enhanced by prior down-regulation of PKC. PKC also exhibits positive cross-talk with CaM kinase. Submaximal activation of CaM kinase by ionomycin is potentiated by concurrent activation of PKC with PMA. Such PMA treatment is found to increase the level of cytosolic calmodulin. Enhanced activation of CaM kinase by PKC may result from PKC-mediated phosphorylation of calmodulin-binding proteins, such as neuromodulin and MARCKS, and the subsequent increase in the availability of previously bound calmodulin for activation of CaM kinase.

Animals↗
PubMed1992

Calmodulin trapping by calcium-calmodulin-dependent protein kinase.

Multifunctional calcium-calmodulin-dependent protein kinase (CaM kinase) transduces transient elevations in intracellular calcium into changes in the phosphorylation state and activity of target proteins. By fluorescence emission anisotropy, the affinity of CaM kinase for dansylated calmodulin was measured and found to increase 1000 times after autophosphorylation of the threonine at position 286 of the protein. Autophosphorylation markedly slowed the release of bound calcium-calmodulin; the release time increased from less than a second to several hundred seconds. In essence, calmodulin is trapped by autophosphorylation. The shift in affinity does not occur in a site-directed mutant in which threonine at position 286 has been replaced by a non-phosphorylatable amino acid. These experiments demonstrate the existence of a new state in which calmodulin is bound to CaM kinase even though the concentration of calcium is basal. Calmodulin trapping provides for molecular potentiation of calcium transients and may enable detection of their frequency.

Amino Acid Sequence↗
PubMed1992

Persistent signalling and changes in presynaptic function in long-term potentiation.

Long-term potentiation (LTP) is an example of a persistent change in synaptic function in the mammalian brain, thought to be essential for learning and memory. At the synapse between hippocampal CA3 and CA1 neurons LTP is induced by a Ca2+ influx through glutamate receptors of the NMDA (N-methyl-D-aspartate) type (see Collingridge et al 1992, this volume). How does a rise in [Ca2+]i lead to enhancement of synaptic function? We have tested the popular hypothesis that Ca2+ acts via a Ca(2+)-dependent protein kinase. We found that long-lasting synaptic enhancement was prevented by prior intracellular injection of potent and selective inhibitory peptide blockers of either protein kinase C (PKC) or Ca2+/calmodulin-dependent protein kinase II (CaMKII), such as PKC(19-31) or CaMKII(273-302), but not by control peptides. Evidently, activity of both PKC and CaMKII is somehow necessary for the postsynaptic induction of LTP. To determine if these kinases are also involved in the expression of LTP, we impaled cells with microelectrodes containing protein kinase inhibitors after LTP had already been induced. Strikingly, established LTP was not suppressed by a combination of PKC and CaMKII blocking peptides, or by intracellular postsynaptic H-7. However, established LTP remained sensitive to bath application of H-7. Thus, the persistent signal may be a persistent kinase, but if so, the kinase cannot be accessed within the postsynaptic cell. Evidence for a presynaptic locus of expression comes from our studies of quantal synaptic transmission under whole-cell voltage clamp. We find changes in synaptic variability expected to result from enhanced presynaptic transmitter release, but little or no increase in quantal size. Furthermore, miniature synaptic currents in hippocampal cultures are increased in frequency but not amplitude as a result of a glutamate-driven postsynaptic induction. The combination of postsynaptic induction and presynaptic expression necessitates a retrograde signal from the postsynaptic cell to the presynaptic terminal.

Animals↗
PubMed1992

Case report: mesenteric lipoblastoma.

A child with mesenteric lipoblastoma is presented. The computed tomographic (CT) features of this unusual tumour are described and correlated with the sonographic findings. The pre-operative diagnosis may be suggested by these features.

Child, Preschool↗
PubMed1992

Sleep in normal late pregnancy.

Twelve women in their third trimester of pregnancy and 10 age-matched nonpregnant controls underwent complete polysomnography for one night in the laboratory. Seven of the original women returned for a second study 3-5 months postpartum. During late pregnancy, women showed increased wake after sleep onset (WASO) and a lower sleep efficiency in comparison with the control group. The percentage of rapid eye movement (REM) sleep was significantly decreased and the percentage of stage 1 significantly increased compared to the nonpregnant group. At 3-5 months postpartum, a significant reduction in WASO and increased sleep efficiency were noted. However, only a slight increase was noted in REM sleep during the postpartum period compared to the prepartum period. The most frequent sleep complaints in the pregnant group were restless sleep, low back pain, leg cramps and frightening dreams. In summary, in accordance with their complaints, women in their third trimester demonstrated polysomnographic patterns of sleep maintenance insomnia.

Adult↗
PubMed1992

Neuronal Ca2+/calmodulin-dependent protein kinases.

Widespread localization, responsiveness to numerous signal transduction systems, and broad substrate specificity enable the multifunctional CaM kinase to mediate regulation of many cellular functions. The abundance and diversity of CaM kinase substrates attest to its role as a multifunctional kinase. However, expanded identification of its in situ substrates as well as the consequences of their regulation by phosphorylation needs to be accomplished. Recently identified substrates have contributed to the list of potential functions for the CaM kinase. CREB is a hormonally stimulated transcriptional activator, and CaM kinase may lie on the pathway to its activation. This pathway could provide an interface between the potentiation of Ca2+ signals by CaM kinase and longer-term modifications of neuronal gene expression. The ryanodine receptor, as well as phospholamban, are involved in cardiac Ca2+ homeostasis, and their regulation by CaM kinase phosphorylation suggests the possibility of some feedback control of intracellular Ca2+ levels by CaM kinase. Regulation of neuronal plasticity by phosphorylation of synapsin I and of postsynaptic substrates necessary for long-term potentiation is another dynamic area of investigation. The study of substrates and their functions promises to continue providing exciting insights into the control of cellular signalling by Ca2+. Molecular cloning has enabled structural comparison of neuronal isoforms of the kinase, and has revealed the existence of closely related subunits. Subunits identified to data differ substantially only in two small variable domains, yet their expression in various tissues and during the course of development is precisely controlled. What unique properties do these small variable domains impart to the different isoforms? What directs high concentrations of kinase to a particular subcellular localization, and especially to the PSD? Further molecular cloning will undoubtedly determine whether other multifunctional CaM kinases with unique structures and properties exist. Finally, studies on the autoregulatory properties of CaM kinase have provided a fascinating picture of how this molecule can alone encode responses to Ca2+ signals, potentiating both the duration and magnitude of its activity. Autophosphorylation of the Thr286 autonomy site both traps calmodulin and permits Ca(2+)-independent activity after calmodulin dissociates. Further analysis of the role of the holoenzyme structure in these modulations will help clarify remaining mechanistic questions. Studies performed during the past few years have clearly established that this Ca(2+)-independent activity is generated in situ in response to a variety of cell stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1992

Urinary and amniotic epidermal growth factor during normal and abnormal pregnancies. A comparison based upon umbilical Doppler velocimetry.

Fetal growth retardation is associated with abnormal umbilical flow velocity. We have begun a systematic study of growth factors and their relationship to this specific pattern of growth retardation. Using a specific double-antibody epidermal growth factor (EGF) 125I-radioimmunoassay, we studied urinary EGF in normal pregnancy from 5 to 42 weeks of gestation, and amniotic fluid EGF from 18 to 24 weeks. EGF levels increased from early pregnancy until 21-28 weeks, when they declined to a level at term similar to non-pregnant controls and first-trimester pregnancy levels. There was no significant difference in urinary EGF levels between women delivering appropriate-for-gestational-age (AGA) infants, and those delivering small-for-gestational-age infants (SGA). We conclude that the urinary EGF is not different in the SGA pregnancy from normal pregnancy.

Amniotic Fluid↗
PubMed1992

Uterine-umbilical artery Doppler velocimetry in pregnant women with systemic lupus erythematosus.

We evaluated continuous wave uterine-umbilical artery Doppler velocimetry for predicting pregnancy outcome in women with systemic lupus erythematosus (SLE). Lupus anticoagulant (LAC) and anticardiolipin (ACL) antibody status also were correlated with Doppler results and outcome. Three Doppler vascular patterns were identified in 27 pregnancies of 26 women with SLE. Patients with normal flow velocity in both vessels had normal outcomes (n = 18). Reduced flow velocity of the umbilical artery only was present in five women, whose newborn infants were of lesser gestational age and birthweight, two being small for gestational age. In four pregnancies reduced flow velocity was noted in both vessels. These cases had the poorest outcome, with three perinatal losses and all fetuses being small for gestational age. Doppler velocimetry showed 100% sensitivity and negative predictive value in the detection of the small for gestational age fetus and abnormal antepartum fetal heart rate tracing. Fourteen of 18 women with normal Doppler studies did not have preeclampsia or SLE flare-ups, whereas all nine women with abnormal Doppler studies had such complications. In all 27 pregnancies the women were screened for LAC, and 21 women also were tested for the ACL antibody. Poor correlation was found between antiphospholipid antibody status and Doppler results in three of the six pregnancies with positive antibody testing the patients had normal Doppler studies and outcomes. Thus, Doppler velocimetry may help determine when these substances will affect the outcome adversely. In this study the umbilical-placental vascular system was affected more often. Uterine-umbilical arterial Doppler velocimetry uniquely identified the fetus at risk for adverse perinatal outcome in pregnancies complicated by SLE. Thus, it is a potentially valuable tool in clarifying the pathophysiology and in the management of SLE in pregnancy.

Adult↗