Functional expression of a rapidly inactivating neuronal calcium channel

Diverse types of calcium channels in vertebrate neurons are important in linking electrical activity to transmitter release, gene expression and modulation of membrane excitability. Four classes of Ca2+ channels (T, N, L and P-type) have been distinguished on the basis of their electrophysiological and pharmacological properties. Most of the recently cloned Ca2+ channels fit within this functional classification. But one major branch of the Ca2+ channel gene family, including BII (ref. 15) and doe-1 (ref. 16), has not been functionally characterized. We report here the expression of doe-1 and show that it is a high-voltage-activated (HVA) Ca2+ channel that inactivates more rapidly than previously expressed calcium channels. Unlike L-type or P-type channels, doe-1 is not blocked by dihydropyridine antagonists or the peptide toxin omega-Aga-IVA, respectively. In contrast to a previously cloned N-type channel, doe-1 block by omega-CTx-GVIA requires micromolar toxin and is readily reversible. Unlike most HVA channels, doe-1 also shows unusual sensitivity to block by Ni2+. Thus, doe-1 is an HVA Ca2+ channel with novel functional properties. We have identified a Ca2+ channel current in rat cerebellar granule neurons that resembles doe-1 in many kinetic and pharmacological features.

Alterations in circulating blood volume during polymicrobial sepsis

Although a great deal is known concerning the pathophysiology of sepsis, it is not clear whether circulating blood volume (CBV) is altered under such conditions. To study, this, rats were subjected to sepsis by cecal ligation and puncture (CLP). Immediately after CLP or sham operation, the animals received 3 ml/100 g body weight normal saline subcutaneously. CBV was determined by using in vivo indocyanine green (ICG) clearance at 2, 5, 10, or 20 hr after CLP or sham operation. This technique does not require any blood sampling. Serum glutamic pyruvic transaminase (SGPT) and glutamic oxaloacetic transaminase (SGOT) were assayed enzymatically as indicators of hepatocyte damage. Hepatic microcirculation was assessed at a selected time point (10 hr post-CLP) by using laser Doppler flowmetry and colloidal carbon infusion techniques. The results indicate that CBV, as determined by ICG clearance, remained unchanged up to 10 hr following the onset of sepsis (i.e., early sepsis) but decreased significantly at 20 hr after CLP (late sepsis). However, systemic hematocrit increased significantly at 5, 10, and 20 hr after CLP, indicating that plasma volume decreased at those time points. This suggests that there may be limitations in accurately assessing CBV at 5 and 10 hr after CLP, i.e., during the hyperdynamic circulatory state of sepsis, using the ICG clearance method. Moreover, SGPT and SGOT levels increased significantly at 10 hr, and the levels increased further at 20 hr post-CLP. In contrast, microvascular blood flow and carbon-perfused areas in the liver were significantly increased at 10 hr post-CLP.

The SH2/SH3 domain-containing protein GRB2 interacts with tyrosine-phosphorylated IRS1 and Shc: implications for insulin control of ras signalling

GRB2, a small protein comprising one SH2 domain and two SH3 domains, represents the human homologue of the Caenorhabditis elegans protein, sem-5. Both GRB2 and sem-5 have been implicated in a highly conserved mechanism that regulates p21ras signalling by receptor tyrosine kinases. In this report we show that in response to insulin, GRB2 forms a stable complex with two tyrosine-phosphorylated proteins. One protein is the major insulin receptor substrate IRS-1 and the second is the SH2 domain-containing oncogenic protein, Shc. The interactions between GRB2 and these two proteins require ligand activation of the insulin receptor and are mediated by the binding of the SH2 domain of GRB2 to phosphotyrosines on both IRS-1 and Shc. Although GRB2 associates with IRS-1 and Shc, it is not tyrosine-phosphorylated after insulin stimulation, implying that GRB2 is not a substrate for the insulin receptor. Furthermore, we have identified a short sequence motif (YV/IN) present in IRS-1, EGFR and Shc, which specifically binds the SH2 domain of GRB2 with high affinity. Interestingly, both GRB2 and phosphatidylinositol-3 (PI-3) kinase can simultaneously bind distinct tyrosine phosphorylated regions on the same IRS-1 molecule, suggesting a mechanism whereby IRS-1 could provide the core for a large signalling complex. We propose a model whereby insulin stimulation leads to formation of multiple protein--protein interactions between GRB2 and the two targets IRS-1 and Shc. These interactions may play a crucial role in activation of p21ras and the control of downstream effector molecules.

Molecular diversity of Ca2+ channel alpha 1 subunits from the marine ray Discopyge ommata

In many neurons, transmitter release from presynaptic terminals is triggered by Ca2+ entry via dihydropyridine-insensitive Ca2+ channels. We have looked for cDNAs for such channels in the nervous system of the marine ray Discopyge ommata. One cDNA (doe-2) is similar to dihydropyridine-sensitive L-type channels, and two cDNAs (doe-1 and doe-4) are similar to the subfamily of dihydropyridine-insensitive non-L-type channels. doe-4, which encodes a protein of 2326 aa, most closely resembles a previously cloned N-type channel. doe-1, which encodes a protein of 2223 aa, is a member of a separate branch of the non-L-type channels. Northern blot analysis reveals that doe-1 is abundant in the forebrain. doe-4 is more plentiful in the electric lobe and, therefore, may control neurotransmitter release in motor nerve terminals. These results show that the familial pattern of Ca(2+)-channel genes has been preserved from a stage in evolution before the divergence of higher and lower vertebrates > 400 million years ago. The cloning of these channels may be a useful starting point for elucidating the role of the Ca2+ channels in excitation-secretion coupling in nerve terminals.

Cocapping of the leukoadhesin molecules complement receptor type 3 and lymphocyte function-associated antigen-1 with Fc gamma receptor III on human neutrophils. Possible role of lectin-like interactions

We have tested the possible physical interactions between the iC3b receptor (CR3), lymphocyte function-associated Ag-1, and class III Fc gamma receptor (Fc gamma RIII) at neutrophil surfaces. Cells were labeled using fluorochrome-conjugated Fab or F(ab')2 fragments of antireceptor mAb. Labeled receptors were capped using second-step F(ab')2 fragments of goat anti-mouse Fab antiserum. After 20 min at 37 degrees C, 68% of the cells capped the anti-CR3 plus second-step complex. Capping was time, temperature, and cytochalasin B sensitive. When capped cells were probed with Fab' or F(ab')2 fragments of anti-Fc gamma RIII labeled with a distinct fluorochrome, 41% of the cells cocapped Fc gamma RIII. Indistinguishable results were obtained when potential antibody combining sites within caps were blocked with a large excess of Fab or F(ab')2 fragments. When Fc gamma RIII was capped, 49% of the cells cocapped CR3. Similarly, LFA-1 cocapped with both CR3 and Fc gamma RIII. Importantly, other membrane components including HLA class I, Mo5, CD13, CR type 1, and IL-8 receptors and N-4-nitrobenzo-2-oxa-1, 3-diszole L-alpha-dimyristoyl phosphatidylethanolamine did not cocap with CR3. However, the positive control Con A did cocap with CR3 and Fc gamma RIII. We next evaluated the effect of saccharides on CR3-Fc gamma RIII cocapping and found that 0.15 M N-acetyl-D-glucosamine (NADG), alpha-methyl-D-mannoside, and D-mannose significantly inhibited cocapping by 70, 58, and 48%, respectively. No inhibition was obtained using glucose, galactose, N-acetyl-neuraminic acid, fucose, sorbitol, fructose, or sucrose. Similarly, Fc gamma RIII-lymphocyte function-associated-1 cocapping was inhibited by NADG. However, the cocapping of CR3 with lymphocyte function-associated-1 or Con A were not affected by 0.15 M NADG, which suggests that NADG inhibition of leukoadhesin-Fc gamma RIII cocapping is not due to a general effect of NADG on capping. Inasmuch as Fc gamma RIII is a glycophospholipid-linked membrane protein, we speculate that it interacts with CR3 and/or lymphocyte function-associated-1 via lectin-like interactions.

Cocapping of the leukoadhesin molecules complement receptor type 3 and lymphocyte function-associated antigen-1 with Fc gamma receptor III on human neutrophils. Possible role of lectin-like interactions

We have tested the possible physical interactions between the iC3b receptor (CR3), lymphocyte function-associated Ag-1, and class III Fc gamma receptor (Fc gamma RIII) at neutrophil surfaces. Cells were labeled using fluorochrome-conjugated Fab or F(ab')2 fragments of antireceptor mAb. Labeled receptors were capped using second-step F(ab')2 fragments of goat anti-mouse Fab antiserum. After 20 min at 37 degrees C, 68% of the cells capped the anti-CR3 plus second-step complex. Capping was time, temperature, and cytochalasin B sensitive. When capped cells were probed with Fab' or F(ab')2 fragments of anti-Fc gamma RIII labeled with a distinct fluorochrome, 41% of the cells cocapped Fc gamma RIII. Indistinguishable results were obtained when potential antibody combining sites within caps were blocked with a large excess of Fab or F(ab')2 fragments. When Fc gamma RIII was capped, 49% of the cells cocapped CR3. Similarly, LFA-1 cocapped with both CR3 and Fc gamma RIII. Importantly, other membrane components including HLA class I, Mo5, CD13, CR type 1, and IL-8 receptors and N-4-nitrobenzo-2-oxa-1, 3-diszole L-alpha-dimyristoyl phosphatidylethanolamine did not cocap with CR3. However, the positive control Con A did cocap with CR3 and Fc gamma RIII. We next evaluated the effect of saccharides on CR3-Fc gamma RIII cocapping and found that 0.15 M N-acetyl-D-glucosamine (NADG), alpha-methyl-D-mannoside, and D-mannose significantly inhibited cocapping by 70, 58, and 48%, respectively. No inhibition was obtained using glucose, galactose, N-acetyl-neuraminic acid, fucose, sorbitol, fructose, or sucrose. Similarly, Fc gamma RIII-lymphocyte function-associated-1 cocapping was inhibited by NADG. However, the cocapping of CR3 with lymphocyte function-associated-1 or Con A were not affected by 0.15 M NADG, which suggests that NADG inhibition of leukoadhesin-Fc gamma RIII cocapping is not due to a general effect of NADG on capping. Inasmuch as Fc gamma RIII is a glycophospholipid-linked membrane protein, we speculate that it interacts with CR3 and/or lymphocyte function-associated-1 via lectin-like interactions.

SH2 domains exhibit high-affinity binding to tyrosine-phosphorylated peptides yet also exhibit rapid dissociation and exchange

src homology 2 (SH2) domains of intracellular signaling molecules such as phospholipase C-gamma and phosphatidylinositol 3'-kinase-associated protein p85 represent recognition motifs for specific phosphotyrosine-containing regions on activated growth factor receptors. The binding of SH2 domains to activated growth factor receptors controls the interaction with signaling molecules and the regulation of their activities. In this report, we describe the kinetic parameters and binding affinities of SH2 domains of p85 toward short phosphotyrosine-containing peptides with the amino acid sequence motif YMXM, derived from a major insulin receptor substrate, IRS-1, by using real time biospecific interaction analysis (BIAcore). Associations were specific and of very high affinity, with dissociation constants of 0.3 to 3 nM, between phosphopeptides and the two separate SH2 domains contained within p85. Nonphosphorylated peptides showed no measurable binding, and the interactions were specific for the primary sequence very close to the phosphotyrosine residue. Moreover, the interactions between phosphopeptides and SH2 domains of other signaling molecules were of much lower affinity. Interestingly, the binding of the SH2 domains to the tyrosine-phosphorylated peptides was of high affinity as a result of a very high on rate, of 3 x 10(7) to 40 x 10(7)/M/s; at the same time, the rate of dissociation, of 0.11 to 0.19/s, was rapid, allowing for rapid exchange of associating proteins with the tyrosine phosphorylation sites.

Lipoperoxidative damage in experimental rabbits with atherosclerosis

The extent of lipoperoxidation in experimental rabbits with atherosclerosis was determined dynamically during the experimental period of 65 days. Lipoperoxide (LPO) levels and selenium-dependent glutathions peroxidase (SeGSHPx) activities in liver, aorta, heart muscle, plasma erythrocyte (RBC) and platelet were examined on the 65th day. The results showed that the potential anti-lipoperoxidation in the atherosclerotic rabbits was decreased significantly, and the tissues were suffered from lipoperoxidative damage. It seems that there is a close relationship between lipoperoxidative damage and the development of atherosclerosis.

Transient activation of a distinct serine protein kinase is responsible for 27-kDa heat shock protein phosphorylation in mitogen-stimulated and heat-shocked cells

We have investigated the phosphorylation of HSP27, a 27-kDa heat shock protein which is involved in cellular thermoresistance and is also an early target of phosphorylation during heat shock and cell stimulation by a variety of growth and differentiation factors. HSP27 is transiently phosphorylated after shifting Chinese hamster cells from their normal temperature of 37 to 44 degrees C. The phosphorylation correlated in time with the transient activation of specific HSP27 protein kinase activities. HSP27 kinase was also induced to maximal levels within 5-15 min following stimulation of quiescent cells with heat shock, serum, thrombin, or basic fibroblast growth factor. Extracts from quiescent cells stimulated by heat shock or serum were analyzed after sequential chromatography on cation exchange and hydroxylapatite columns. In both cases, a single and identical peak of HSP27 kinase activity was obtained, suggesting that the same protein kinase was induced. The HSP27 kinase efficiently phosphorylated recombinant Chinese hamster HSP27 or the synthetic peptide RALNRQLSSGV containing the major in vivo phosphorylation site of rodent HSP27. The kinase was inactive toward the ribosomal S6 protein, the peptide RALSSLRA from S6 protein, or the mutant HSP27 proteins with in vivo phosphorylation sites altered to glycine. The partially purified HSP27 kinase had no kinase C, kinase A, or S6 kinase activities; conversely, HSP27 was not a good substrate for these kinases. HSP27 kinase was rapidly inactivated in the presence of acid phosphatase, suggesting that its activity was regulated by phosphorylation. It is suggested that this heat shock- and serum-induced HSP27 kinase is a novel serine kinase which is linked to a major signal transduction cascade.

Evaluation of 90:10 poly(D,L-lactide-co-glycolide) microspheres containing norethisterone: drug release and biodegradation

Poly(D,L-lactide-co-glycolide) (PLG, 90:10) microspheres containing 20% norethisterone (NET) were prepared by solvent evaporation method. Microspheres in the size ranges of 65 to 100 microns were sterilized by irradiation and used for further study. In vitro release showed fairly constant release of NET from the above microspheres over more than 90 days. However, in vivo drug release determined by residual NET analysis after i.m. injection in rats indicated a faster release rate. About 95% of NET was released in a period of 45 days. At the dose of 80 mg of microspheres, vaginal estrus cycles were inhibited for 45 days compared to 27 days for the same dose of NET crystals in rats. Biodegradation of the microspheres was tested by direct measurement of molecular weight losses and SEM observation of morphological changes of the microspheres, which showed continuous erosion in the internal matrix of microspheres with the decrease of molecular weight of PLG until total collapse of microspheres, and biodegradation was faster in rats than in human serum at 37 degrees C in vitro. Total degradation of 90:10 PLG microspheres was less than 7 months in rats and more than 9 months in vitro.

The effect of recombinant GM-CSF and G-CSF on the bone marrow cells of children with acute lymphoblastic leukemia

Colony stimulating factors (CSFs) are glycoprotein hormones that regulate growth and differentiation of hematopoietic progenitor cells. Their use to stimulate granulocyte precursors during periods of neutropenia in patients with acute myeloid leukemia (AML) is limited by their concomitant stimulation of the proliferation of myeloblasts. The effects of these agents on leukemic lymphoblasts is not entirely known. We have investigated the in vitro effects of granulocyte-CSF (G-CSF) and granulocyte/macrophage-CSF (GM-CSF) on leukemic cells from children with acute lymphoblastic leukemia (ALL). DNA synthesis of bone marrow cells from 22 children with ALL, either at diagnosis or in relapse, was examined with and without CSFs. Proliferative potential was also tested in a clonogenic assay with 13 bone marrow specimens. These factors did not stimulate the growth of ALL cells in either assay. Our results indicate that G-CSF and GM-CSF should be able to stimulate granulocyte proliferation without enhancing leukemic proliferation during periods of neutropenia in children with ALL.

[The effect of 211At labelled monoclonal antibody against gastric cancer on DNA, RNA and protein synthesis in gastric cancer cell]

By means of nuclide precursor incorporation, the effects of 211At labelled monoclonal antibody against gastric cancer (211At-3H11McAb) on DNA, RNA and protein synthesis in gastric cancer cell were studied. The results show that 211At-3H11McAb and Na211At-3 inhibit 3H-TdR, 3H-UR and 3H-Leu incorporation, especially 3H-UR incorporation, into gastric cancer cell at 3.7 x 10(4)Bq and 1.85 x 10(5)Bq; the inhibiting rates depend on concentration. The DNA biosynthesis in gastric cancer cell gradually recover after the drug is removed, suggesting that the drug should exert an inhibiting action on DNA biosynthesis in tumor cell through interference of DNA metabolism.

Differential alterations in microvascular perfusion in various organs during early and late sepsis

Although cellular dysfunction occurs very early in sepsis, it remains controversial whether this is solely due to a decrease in tissue perfusion. Recent studies have indicated that while active hepatocellular function was depressed, hepatic surface microvascular blood flow (MBF) increased in early sepsis but decreased in late sepsis as produced by cecal ligation and puncture (CLP). However, it is not known whether microvascular hyperperfusion in early sepsis and microvascular hypoperfusion in late sepsis are common events in other organs under such conditions. To study this, rats were subjected to sepsis by CLP, after which these and the corresponding shams received 3 ml/100 g body wt normal saline. Microvascular perfusion and MBF in various tissues were assessed by colloidal carbon infusion and laser-Doppler flowmetry, respectively, at 5 h (i.e., early sepsis) or 20 h (late sepsis) after CLP or sham operation. Carbon-perfused areas were quantitated by an Optomax image analyzer. The results indicate that the carbon-perfused areas and MBF in the liver, renal cortex, spleen, and small intestinal serosa (only MBF) increased significantly 5 h after CLP. In late sepsis, however, the carbon-perfused areas and MBF were found to be significantly decreased. A highly linear relationship was observed between the changes of carbon-perfused areas and MBF during sepsis in the tested organs. Thus the microvascular responses in the fluid-resuscitated sepsis model are characterized by hyperperfusion in the early stage and hypoperfusion in the late stage of sepsis in the tested tissues. The cellular dysfunctions observed during the early stage of sepsis are, therefore, not due to any reduction in tissue perfusion.

Protective effects of preheparinization on the microvasculature during and after hemorrhagic shock

Despite the fact that trauma patients are not heparinized at the time of injury, most models of hemorrhagic shock involve heparinization before the initiation of hemorrhage. To determine whether preheparinization has any effects on the microvasculature of organs during or after hemorrhage, rats (with and without preheparinization) were bled to a mean arterial blood pressure (BP) of 40 mm Hg. In two groups, this pressure was maintained by withdrawing additional blood until BP could no longer be maintained at 40 mm Hg (maximal bleedout, MB). In another two groups, the BP was maintained at 40 mm Hg until 40% of the MB volume was returned in the form of lactated Ringer's solution. The rats were then resuscitated with four times the volume of MB with lactated Ringer's. At MB or immediately after resuscitation, colloidal carbon black was rapidly infused and the liver, kidney, and spleen were excised, fixed, and sectioned. In additional animals, blood samples for platelet counts and total body fibrinogen estimates were taken before hemorrhage and at MB or at the end of resuscitation. The results indicate that at MB, microvascular patency in the kidney and liver was significantly depressed in the nonheparinized rats but not depressed in the preheparinized rats. This protective effect of heparin is not directly attributable to its anticoagulant properties, since there were no differences in the consumption of platelets or fibrinogen between the nonheparinized and preheparinized groups. Although the microvascular patency improved with resuscitation in the nonheparinized group, the glomeruli counts and perfusion of the spleen remained significantly lower than in the preheparinized group.(ABSTRACT TRUNCATED AT 250 WORDS)

ATP-MgCl2 restores renal microcirculation following trauma and severe hemorrhage

Although ATP-MgCl2 enhances the recovery of renal function after ischemia and reperfusion, it is not known whether this agent has any beneficial effects on renal microcirculation and function in a nonheparinized model of trauma and severe hemorrhage. To study this, a midline laparotomy was performed (i.e., trauma induced) and the rats were bled to and maintained at a mean arterial pressure of 40 mmHg (1 mmHg = 133.32 Pa) until 40% of the maximum shed blood volume was returned in the form of Ringer's lactate (RL) solution. Animals were then resuscitated with 4 times the volume of the shed blood in the form of RL. ATP-MgCl2, 50 mumol/kg body weight, or an equivalent volume of saline, was infused intravenously during and following resuscitation. Renal microcirculation was examined by using colloidal carbon infusion and laser Doppler flow-metry. Glomerular filtration rate (GFR) was assessed with [3H]inulin clearance and cardiac output (CO) was determined by dye dilution technique. The results indicate that the depressed renal microcirculation following hemorrhage and resuscitation was restored by ATP-MgCl2 treatment. GFR was significantly higher in ATP-MgCl2-treated than saline-treated rats. ATP-MgCl2 also increased urine output, restored the decreased CO, and prevented the occurrence of renal edema after hemorrhage and resuscitation. Thus, ATP-MgCl2 appears to be a useful adjunct to crystalloid resuscitation following trauma and severe hemorrhagic shock even in the absence of blood resuscitation.

Human HSP27 is phosphorylated at serines 78 and 82 by heat shock and mitogen-activated kinases that recognize the same amino acid motif as S6 kinase II

The intracellular concentration of the 27-kDa mammalian heat shock protein, HSP27, increases several-fold after heat and other metabolic stresses and is closely associated with the acquisition of thermotolerance. Posttranslational modifications may also affect the function of HSP27. Heat shock of HeLa cell cultures, or treatment with arsenite, phorbol ester, or tumor necrosis factor, caused a rapid phosphorylation of preexisting HSP27 and the appearance of three phosphorylated isoforms, HSP27 B, C, and D. Digestion with trypsin and fractionation of the peptides by reverse phase high performance liquid chromatography revealed three 32P-labeled phosphopeptides. Microsequence analysis identified peak I as Ala76-Leu77-Ser78-Arg79 and peak II as Gln80-Leu81-Ser82-Ser83-Gly84-Val85- Ser86-Glu87-Ile88-Arg89; peak III contained the undigested peptide pair Ala76-Arg89. Ser82 was the major site and Ser78 the minor site of phosphorylation. Mutant proteins with Ser78 or Ser82 altered to glycine or Ser78-Ser82 double mutants were phosphorylated to reduced extents in vivo after heat or arsenite treatment. Ser78 and Ser82 (and Ser15) occur in the sequence motif RXXS, which is recognized by ribosomal protein S6 kinase II. Mitogenic stimulation of serum-deprived, Go-arrested Chinese hamster cells with serum, thrombin, or fibroblast growth factor also stimulated phosphorylation of HSP27 Ser78 and Ser82, and mitogenic stimulation and heat shock activated protein kinase activities that phosphorylated HSP27 and protein S6 in vitro. These results suggest that HSP27 may exert phosphorylation-activated functions linked with growth signaling pathways in unstressed cells. A homeostatic function at this level could protect cells from adverse effects of signal transduction systems which may be activated inappropriately during stress.