Autocides produced by Myxococcus xanthus.

Ethanol extracts of Myxococcus xanthus contained several substances, referred to as autocides, which were bactericidal to the producing strain but showed no activity against other bacteria. The autocides were produced by growing cells and remained largely cell bound throughout the growth cycle; ca. 5% of the autocidal activity was found in the supernatant fluid at the time cell lysis began. The autocides were separated by sequential-column and thin-layer chromatography into five active fractions (AM I through AM V). Each of the fractions was at least 20 times more active against M. xanthus than against the other gram-negative or gram-positive bacteria tested. AM I, AM IV, and AM V were inactive against yeasts, whereas a mixture of fractions AM II and AM III was active against Rhodotorula sp. At low concentrations, AM I reversibly inhibited the growth of M. xanthus; at higher concentrations of AM I, the cells lysed within 1 h. The lowest concentration of AM IV that showed any activity caused rapid cell death and lysis. The mode of action of the major autocide, AM V, was different from that of AM I and AM IV. During the initial 2 h of treatment, the viable count of M. xanthus cells remained constant; during the next few hours killing occurred without lysis; within 24 h lysis was complete. The autocidal activity of each of the fractions was expressed when the cells were suspended in buffer, as well as in growth medium. The possible role of autocides in developmental lysis of M. xanthus is discussed.     

Female sex hormone and nephropathy in Cohen diabetic rat (genetically selected sucrose-fed)

In the Cohen diabetic rat (genetically-selected sucrose-fed) ovariectomy resulted in a significantly decreased incidence of nephropathy, while estradiol treatment to the ovariectomized animal increased the rate of nephropathy to the levels occurring in the uncastrated untreated diabetic female. In the male diabetic animal orchidectomy caused a slight decrease in the rate of nephropathy whereas estradiol treatment to the orchidectomized animal resulted in a slight increase in the rate. No difference was found between the ovariectomized and the uncastrated diabetic female as to the spontaneous blood glucose, plasma insulin, serum cholesterol or TG levels, but a significant difference was found in their plasma estradiol levels.     

Biochemical characterization of complex formation by human erythrocyte spectrin, protein 4.1, and actin

Ternary complex formation between the major human erythrocyte membrane skeletal proteins spectrin, protein 4.1, and actin was quantified by measuring cosedimentation of spectrin and band 4.1 with F-actin. Complex formation was dependent upon the concentration of spectrin and band 4.1, each of which promoted the binding of the other to F-actin. Simultaneous measurement of the concentrations of spectrin and band 4.1 in the sedimentable complex showed that a single molecule of band 4.1 was sufficient to promote the binding of a spectrin dimer to F-actin. However, the molar ratio of band 4.1/spectrin in the complex was not fixed, ranging from approximately 0.6 to 2.2 as the relative concentration of added spectrin to band 4.1 was decreased. A mole ratio of 0.6 band 4.1/spectrin suggests that a single molecule of band 4.1 can promote the binding of more than one spectrin dimer to an actin filament. Saturation binding studies showed that in the presence of band 4.1 every actin monomer in a filament could bind at least one molecule of spectrin, yielding ternary complexes with spectrin/actin mole ratios as high as 1.4. Electron microscopy of such complexes showed them to consist of actin filaments heavily decorated with spectrin dimers. Ternary complex formation was not affected by alteration in Mg2+ or Ca2+ concentration but was markedly inhibited by KCl above 100 mM and nearly abolished by 10 mM 2,3-diphosphoglycerate or 10 mM adenosine 5'-triphosphate. Our data are used to refine the molecular model of the red cell membrane skeleton.     

Possible change in noradrenergic receptor sensitivity following methylphenidate treatment: Growth hormone and MHPG response to clonidine challenge in children with attention deficit disorder and hyperactivity

Growth hormone (GH) and 3-methoxy-4-hydroxyphenelethylene glycol (MHPG) response was measured hourly for 4 hours in 8 children with Attention Deficit Disorder with Hyperactivity (ADD+H) following an acute single-dose of clonidine. The clonidine challenge was repeated before, during, and one day after 12 weeks of treatment with methylphenidate (MPH). Before MPH treatment, the plasma growth hormone (GH) rose to 31.3 ± 4.6 (Mean ± SE) ng/ml; during MPH treatment, the GH peak was only 14.8 ± 3.2 ng/ml; one day after discontinuation of MPH, GH rose to only 20.8 ± 3.9 ng/ml. MHPG release was inhibited by clonidine in all treatment conditions but tended to be more decreased during MPH treatment. Some children with ADD+H may have hypersensitivity of the post-synaptic alpha-1 noradrenergic receptor which is diminished by MPH treatment. The extent to which these effects are pharmacological or represent a change in receptor sensitivity requires further study.     

Role of hydrophilic bile acids and of sterols on cholelithiasis in the hamster

The effect of various dietary additions such as cholesterol, beta-sitosterol, bile acids, and bile acid analogs on gallstone formation was studied in the hamster. Gallstones were formed in 50% of the animals fed a high glucose, fat-free diet. Administration of 0.2% cholesterol or 1% beta-sitosterol had no effect on the incidence of gallstones. Ursodeoxycholic acid (0.5%) and its analog ursodeoxy-oxazoline [2-(3 alpha, 7 beta-dihydroxy-24-nor-5 beta-cholanyl)-4,4-dimethyl-2- oxazoline] were ineffective in preventing gallstones. Hyodeoxycholic acid and hyodeoxy-oxazoline [2-(3 alpha,6 alpha-dihydroxy-24-nor-5 beta-cholanyl)-4,4-dimethyl-2- oxazoline] at the same dosage effectively prevented gallstones, while the trihydroxy bile acid, hyocholic acid, was not effective. Of all the dietary regimens tested, only hyodeoxycholic acid significantly lowered serum cholesterol. The lithogenic diet produced a five-fold increase in hepatic HMG-CoA reductase activity; this activity was not affected by dietary cholesterol or beta-sitosterol. Hyodeoxycholic acid and hyocholic acid feeding increased the reductase activity by an additional 50% while the other bile acids had no effect. beta-Sitosterol doubled the cholesterol 7 alpha-hydroxylase activity whereas hyodeoxy-oxazoline lowered it. Hyodeoxycholic acid-fed animals had significantly lower cholesterol absorption than the animals on the lithogenic diet alone. Biliary cholesterol content increased dramatically in the animals fed the lithogenic diet and was increased still further by ursodeoxycholic acid, hyodeoxycholic acid, and hyodeoxy-oxazoline. These data show that hyodeoxycholic acid and hyodeoxy-oxazoline do not prevent gallstones by inhibiting hepatic cholesterol synthesis or biliary cholesterol secretion.     

Electrical effects of potassium and bicarbonate on proximal tubule cells ofNecturus

Summary The effects of stepwise concentration changes of K⁺ and HCO ₃ ^– in the basolateral solution on the basolateral membrane potential (V _bl) of proximal tubule cells of the doubly-perfusedNecturus kidney were examined using conventional microelectrodes. Apparent transference numbers were calculated from changes inV _bl after alterations in external K⁺ concentration from 1.0 to 2.5mm (t _{K, 1.0–2.5}), 2.5 to 10, and in external HCO ₃ ^– concentration (at constant pH) from 5 to 10mm (t _{HCO3, 5–10}), 10 to 20, or 10 to 50.t _{K, 2.5–10} was 0.38±0.02 under control conditions but was sharply reduced to 0.08±0.03 (P>0.001) by 4mm Ba⁺⁺. This concentration of Ba⁺⁺ reducedV _bl by 9±1 mV (at 2.5 external K⁺). Perfusion with SITS (5×10^–4 m) for 1 hr hyperpolarizedV _bl by 10±3 mV and increasedt _{K, 2.5–10} significantly to 0.52±0.01 (P<0.001). Ba⁺⁺ application in the presence of SITS depolarizedV _bl by 22±3 mV. In control conditionst _{HCO3, 10–50} was 0.63±0.05 and was increased to 0.89±0.07 (P<0.01) by Ba⁺⁺ but was decreased to 0.14±0.02 (P<0.001) by SITS. In the absence of apical and basolateral chloride, the response ofV _bl to bicarbonate was diminished but still present (t _{HCO3, 10–20} was 0.35±0.03). Intracellular pH, measured with liquid ion-exchange microelectrodes, increased from 7.42±0.19 to 7.57±0.17 (P<0.02) when basolateral bicarbonate was increased from 10 to 20mm at constant pH. These data show that the effects of bicarbonate onV _bl are largely independent of effects on the K⁺ conductance and that there is a significant current-carrying bicarbonate pathway in the basolateral membrane. Hence, both K⁺ and HCO ₃ ^– gradients are important in the generation ofV _bl, and their relative effects vary reciprocally.     

Regulation of the basolateral potassium conductance of theNecturus proximal tubule

Summary Two methods, the measurement of the response of the basolateral membrane potential (V _bl) of proximal tubule cells ofNecturus to step changes in basolateral K⁺ concentration, and cellular cable analysis, were used to assess the changes in basolateral potassium conductance (G _K) caused by a variety of maneuvers. The effects of some of these maneuvers on intracellular K⁺ activity (a _K ⁱ ) were also evaluated using double-barreled ion-selective electrodes. Perfusion with 0mm K⁺ basolateral solution for 15 min followed by 45 min of 1mm K⁺ solution resulted in a fall in basolateral potassium (apparent) transference number (t _K),V _bl anda _K ⁱ . Results of cable analysis showed that total basolateral resistance,R _b , rose. The electrophysiological effects of additional manipulations, known to inhibit net sodium reabsorption across the proximal tubular epithelium ofNecturus, were also investigated. Ouabain caused a fall int _K accompanied by large decreases ina _K ⁱ andV _bl. Lowering luminal sodium caused a fall int _K and a small reduction inV _bl. Selective reduction of peritubular sodium, a maneuver that has been shown to block sodium transport from lumen to peritubular fluid, also resulted in a significant decrease int _K. These results suggest thatG _K varies directly with rate of transport of the sodium pump, irrespective of the mechanism of change in pump turnover.Part of this material has been presented at the 10th International Conference on Biological Membranes (Cohen & Giebisch, 1984).     

Phosphorylation of tyrosine hydroxylase by calmodulin-dependent multiprotein kinase

Tyrosine hydroxylase purified from rat pheochromocytoma was phosphorylated stoichiometrically by either cyclic AMP-dependent protein kinase or calmodulin-dependent multiprotein kinase from skeletal muscle, but not by five other protein kinases tested. The activity of tyrosine hydroxylase was elevated 3-fold by cyclic AMP-dependent protein kinase, but no activation was observed after phosphorylation by calmodulin-dependent multiprotein kinase. Phosphorylation produced by cyclic AMP-dependent protein kinase and calmodulin-dependent multiprotein kinase was additive, suggesting different sites of phosphorylation. This was confirmed by high-performance liquid chromatography analysis of tryptic phosphopeptides which demonstrated that the major sites phosphorylated by each protein kinase were distinct. A calmodulin-dependent multiprotein kinase that had identical properties and substrate specificity to the skeletal muscle enzyme was partially purified from rat pheochromocytoma. The possibility that this protein kinase is involved in the regulation of tyrosine hydroxylase activity in adrenergic tissue in vivo is discussed.     

Glucocorticoid activation of a calcium-dependent endonuclease in thymocyte nuclei leads to cell death

Dexamethasone and corticosterone kill mouse thymocytes, as measured by eosin uptake, after several hours of in vitro incubation. This killing requires RNA and protein synthesis, because it is inhibited by cycloheximide, emetine, or actinomycin D. An earlier event than cell death is the extensive fragmentation of nuclear DNA into oligonucleosomal subunits; this fragmentation also requires RNA and protein synthesis. The DNA cleavage results from the action of an endonuclease that preferentially cleaves DNA in the linker regions between nucleosomes. This endonuclease is found constitutively in the nuclei of thymocytes and some other cells, and requires calcium and magnesium ions for its activation; if isolated fresh thymocyte nuclei are incubated with these ions, as much as 77% of their DNA is cleaved within 90 min. Thus, the protein for which synthesis is necessary for glucocorticoid-induced thymocyte death is not the endonuclease itself, but is in some way involved in its activation; we suggest that it may be part of a system for transporting calcium into the nucleus. The endonuclease is inhibited by zinc, which also prevents thymocyte death. It appears that glucocorticoids cause thymocyte death by activating an enzyme that rapidly and extensively degrades DNA. This "death from within" is biochemically and morphologically different from toxic or accidental cell death, such as that induced by azide, heat, or antibody and complement treatment. Although mature T cells also contain the endogenous endonuclease, they lack the glucocorticoid-inducible mechanism for activating it, and are thus glucocorticoid-resistant.     

T cell synergy in the primary MLR: proliferative kinetics, effector cell generation, and IL 2 production

A primary rat MLR was initiated, and on each of 8 consecutive days during the evolving culture, an aliquot of cells was separated into its constitutive helper/inducer (W3/25+) and suppressor/cytotoxic (OX8+) T cell subsets by a monoclonal antibody, Degalan-bead immunoadsorbent column technique. This allowed a detailed kinetic analysis of T cell proliferation, the generation of effector cells, and the production of IL 2 by each subset relative to net whole culture supernatant IL 2 activity. The primary MLR demonstrates an early period of helper/inducer cell proliferation, IL 2 production and accumulation, followed by a period of suppressor/cytotoxic cell (OX8+) proliferation and IL 2 consumption during which there are distinct waves of allospecific suppressor, followed by cytotoxic activity. If fresh T cells of the helper/inducer or suppressor/cytotoxic phenotype were preseparated and then cultured alone with irradiated allogeneic stimulator cells, proliferation was noted in both subsets despite no demonstrable IL 2 activity in cultures of the suppressor/cytotoxic cells. Finally, a suppressed primary MLR exhibited proliferative inhibition of both T cell subsets.