Differential regulation of glucose transporter gene expression in adipose tissue or septic rats.

To understand the molecular mechanisms responsible for the sepsis-induced enhanced glucose uptake, we have examined the levels of GLUT4 and GLUT1 mRNA and protein in the adipose tissue of septic animals. Rats were challenged with a nonlethal septic insult where euglycemia was maintained and hexose uptake in adipose tissue was markedly elevated. Northern blot analysis of total RNA isolated from epididymal fat pads indicated differential regulation of the mRNA content for the two transporters: GLUT1 mRNA was increased 2.6 to 4.6-fold, while GLUT4 mRNA was decreased by 2.5 to 2.9-fold. Despite the difference in mRNA levels, both GLUT1 and GLUT4 protein were down regulated in plasma membranes (40% and 25%, respectively) and microsomal membranes (42% and 25%, respectively) of the septic animals. The increased glucose uptake cannot be explained by the membrane content of GLUT1 and GLUT4 protein. Thus, during hypermetabolic sepsis, increased glucose utilization by adipose tissue is dependent on alternative processes.     

Heparin binding to the urokinase kringle domain.

The binding of urokinase to immobilized heparin and dextran sulfate was studied using activity assays of the bound urokinase. The markedly higher binding observed with high M(r) urokinase compared to low M(r) urokinase indicated a role for the amino-terminal fragment (ATF). This was confirmed by the use of inactive truncated urokinase and monoclonal antibodies specific for the ATF in competition assays of urokinase binding. Antibody competition assays suggested a site in the kringle domain, and a synthetic decapeptide Arg-52-Trp-62 from the kringle sequence (kringle numbering convention) was competitive in assays of urokinase binding to dextran sulfate and heparin. Heparin binding to the urokinase kringle was unambiguously demonstrated via 1H NMR spectroscopy at 500 MHz. Effective equilibrium association constants (K(a)*) were determined for the interaction of isolated kringle fragment and low M(r) heparin at pH 7.2. The binding was strong in salt-free 2H2O (K(a)* approximately 57 mM-1) and remained significant in 0.15 M NaCl (K(a)* approximately 12 mM-1), supporting a potential physiological role for the interaction. This is the first demonstration of a function for the kringle domain of urokinase, and it suggests that while the classical kringle structure has specificity for lysine binding, there may also exist a class of kringles with affinity for polyanion binding.     

Product-precursor relationships amongst inositol polyphosphates. Incorporation of [32P]Pi into myo-inositol 1,3,4,6-tetrakisphosphate, myo-inositol 1,3,4,5-tetrakisphosphate, myo-inositol 3,4,5,6-tetrakisphosphate and myo-inositol 1,3,4,5,6-pentakisphosphate in intact avian erythrocytes.

Avian erythrocytes were incubated with myo-[3H]inositol for 6-7 h and with [32P]Pi for the final 50-90 min of this period. An acid extract was prepared from the prelabelled erythrocytes, and the specific radioactivities of the gamma-phosphate of ATP and of both the myo-inositol moieties (3H, d.p.m./nmol) and the individual phosphate groups (32P, d.p.m./nmol) of [3H]Ins[32P](1,3,4,6)P4,[3H]Ins[32P](1,3,4,5)P4, [3H]Ins[32P](3,4,5,6)P4 and [3H]Ins[32P](1,3,4,5,6)P5 were determined. The results provide direct confirmation that one of the cellular InsP4 isomers is Ins(1,3,4,5)P4 which is synthesized by sequential phosphorylation of the 1,4,5 and 3 substitution sites of the myo-Ins moiety, precisely as previously deduced [Batty, Nahorski & Irvine (1985) Biochem. J. 232, 211-215; Irvine, Letcher, Heslop & Berridge (1986) Nature (London) 320, 631-634]. This is compatible with the proposed synthetic route from PtdIns via PtdIns4P, PtdIns(4,5)P2 and Ins(1,4,5)P3. The data also suggest that, in avian erythrocytes, the principle precursor of Ins(1,3,4,5,6)P5 is Ins(3,4,5,6)P4. Furthermore, if the gamma- (and/or beta-) phosphate of ATP is the precursor of the phosphate moieties of Ins(3,4,5,6)P4, then this isomer must be derived from the phosphorylation of Ins(3,4,6)P3. If the gamma- (and/or beta-) phosphate of ATP similarly acts as the ultimate precursor to all of the phosphates of Ins(1,3,4,6)P4, then, in intact avian erythrocytes, the main precursor of Ins(1,3,4,6)P4 is Ins(1,4,6)P3. This contrasts with the expectation, based on results with cell-free systems, that Ins(1,3,4,6)P4 is synthesized by the direct phosphorylation of Ins(1,3,4)P3.     

A myo-inositol D-3 hydroxykinase activity in Dictyostelium.

A soluble ATP-dependent enzyme which phosphorylates myo-inositol has been characterized in Dictyostelium. The myo-inositol kinase activity was partially purified from amoebae by chromatography on DEAE-Sepharose and phenyl-Sepharose columns. The product of both the partially purified activity and of a crude cytosolic fraction was myo-inositol 3-phosphate. The partially purified preparations of myo-inositol kinase (a) possessed a Km for myo-inositol of 120 microM (in the presence of 5 mM-ATP) and for ATP of 125 microM (in the presence of 1 microM-myo-inositol), (b) did not recognize allo-, epi-, muco-, neo-, scyllo-, 1 D-chiro or 1 L-chiro-inositol as substrates, (c) were competitively inhibited by three naturally occurring analogues of myo-inositol: 1 L-chiro-inositol (Ki 49.5 +/- 0.7 microM: the structural equivalent of myo-inositol, except that the D-3 hydroxy moiety is axial), D-3-deoxy-myo-inositol [Ki 103 +/- 1 microM: (-)-viburnitol], and sequoyitol (Ki 271 +/- 7 microM; unlike 1 L-chiro-inositol and D-3-deoxy-myo-inositol, this was a substrate for the kinase), and finally (d) were apparently non-competitively inhibited by myo-inositol 3-phosphate. The product of myo-inositol kinase could be detected in intact amoebae and was a substrate for the first in a series of inositol polyphosphate kinases present in Dictyostelium which ultimately yield myo-inositol hexakisphosphate. The activity of myo-inositol D-3-hydroxykinase in Dictyostelium lysates showed evidence of developmental regulation.     

Agonist-stimulated inositol phosphate metabolism in avian erythrocytes.

1. A screen for agonists capable of stimulating the formation of inositol phosphates in erythrocytes from 5-day-old chickens revealed the presence of a population of phosphoinositidase C-linked purinergic receptors. 2. If chicken erythrocytes prelabelled with [3H]Ins were exposed to a maximal effective dose of adenosine 5'-[beta-thio]diphosphate for 30 s, the agonist-stimulated increment in total [3H]inositol phosphates was confined to [3H]Ins(1,4,5)P3, Ins(1,3,4,5)P4 and InsP2. After 40 min stimulation, the radiolabelling of nearly all of the [3H]inositol phosphates that have been detected in these extracts [Stephens, Hawkins & Downes (1989) Biochem. J. 262, 727-737] had risen. However, some of these increases [especially those in Ins(3,4,5,6)P4 and Ins(1,3,4,5,6)P5] were accountable for almost entirely by increases in specific radioactivity rather than in mass. 3. The effect of purinergic stimulation on the rate of incorporation of [32P]Pi in the medium into the gamma-phosphate group of ATP and InsP4 and InsP5 was also measured. After 40 min stimulation, the incorporation of 32P into Ins(1,3,4,6)P4, Ins(1,3,4,5)P4, Ins(3,4,5,6)P4 and Ins(1,3,4,5,6)P5 was significantly elevated, whereas the mass of the last two and the specific radioactivity of the gamma-phosphate of ATP were unchanged compared with control erythrocyte suspensions. 4. In control suspensions of avian erythrocytes, the specific radioactivity of the individual phosphate moieties of Ins(1,3,4,6)P4 increased through the series 1, 6, 4 and 3 [Stephens & Downes (1990) Biochem. J. 265, 435-452]. This pattern of 32P incorporation is not the anticipated outcome of 6-hydroxy phosphorylation of Ins(1,3,4)P3 [the assumed route of synthesis of Ins(1,3,4,6)P4]. Although adenosine [beta-thio]diphosphate significantly stimulated the accumulation of [3H]Ins(1,3,4)P3, and despite the fact that avian erythrocyte lysates were shown to possess a chromatographically distinct, soluble, ATP-dependent, Ins(1,3,4)P3 6-hydroxykinase activity, purinergic stimulation of intact cells did not significantly alter the pattern of incorporation of [32P]Pi into the individual phosphate moieties of Ins(1,3,4,6)P4. These results suggest that the route of synthesis of this inositol phosphate species is not changed during the presence of an agonist.     

Contractile properties of bronchial smooth muscle with and without cartilage

The majority of in vitro studies on airway smooth muscle have used the trachealis (TSM) as a convenient substitute for muscle from airways that constitute the flow-limiting segment. The latter are technically difficult to work with. However, because the site of maximum resistance to airflow is at the third to seventh generations of the bronchial tree, the trachealis preparation is of limited value. Length-tension and force-velocity properties were therefore studied at optimal length (lo) of canine bronchial smooth muscle (BSM) from which cartilage had been carefully removed. Normalized maximum isometric tension or stress (Po x 10(4) N/m2) for BSM was 7.1 +/- 0.19 (SE), which was similar to that of BSM with cartilage (BSM+C, 6.8 +/- 0.21) but lower than for TSM (18.2 +/- 0.81). At length greater than lo, the BSM+C was stiffer than the BSM. The values of maximum shortening capacity (delta Lmax), obtained directly from isotonic shortening at a load equal to the resting tension at lo, were 0.76 lo +/- 0.03, 0.41 lo +/- 0.02, and 0.24 +/- 0.02 lo for TSM, BSM, and BSM+C, respectively. The BSM and BSM+C delta Lmaxs were different (P less than 0.05). Maximal shortening velocities (Vo) for BSM, elicited at 2, 4, and 8 s by quick release in the course of an isometric contraction were significantly higher than for the BSM+C. Vos showed gradual decreases in all three groups in the later phase of contraction, suggesting the operation of latch bridges.(ABSTRACT TRUNCATED AT 250 WORDS)     

Non-reciprocal cross-incompatibility in Trichogramma deion

In non-reciprocal cross-incompatibility (NRCI), the crossing of a female of a strain A with a male of a strain B results in hybrid offspring, whereas the reciprocal cross produces few or no hybrids. Only females are of hybrid origin in Hymenoptera because they arise from fertilized eggs; males arise from unfertilized (haploid) eggs. Crosses between many strains of Trichogramma deion showed some degree of NRCI. Crosses between a T. deion culture collected in Seven Pines, California (SVP) with one from Marysville, California (MRY) showed an extreme form of NRCI in which practically no female offspring was produced when MRY females were crossed with SVP males. The reciprocal cross produced a close to normal proportion of female and male offspring. Detailed studied of this cross indicated that 1) the female offspring produced in the compatible interstrain cross were not the result of parthenogenesis but were true hybrids, 2) the incompatible interstrain cross did not produce female offspring because fertilized eggs died during development, 3) the death of these eggs could not be prevented by either antibiotic or temperature treatment, 4) cytoplasmically inherited factors causing NRCI could be discounted because backcrossed females with the genome of MRY and the cytoplasm of SVP, exhibit the NRCI relationship characteristic of their genome. Therefore the NRCI between these strains appears to be caused by a modification coded for by the nuclear genes of MRY that results in incompatibility when SVP sperm fertilizes MRY eggs. In addition the level of incompatibility in crosses between the SVP females and MRY males is temperature sensitive, the higher the rearing temperature the lower the level of compatibility.     

Substance P and neurokinin A metabolism by cultured human skeletal muscle myocytes and fibroblasts

A recent study determined that cultured human skeletal muscle adult myoblasts, myotubes, and fibroblasts degraded angiotensins and kinins via neutral endopeptidase-24.11 (NEP-24.11; EC 3.4.24.11) and aminopeptidase N (APN; EC 3.4.11.2). Due to the possible importance of other peptides to skeletal muscle blood flow and function, the present study looked specifically at the metabolism of the neurokinins substance P (SP) and neurokinin A (NKA) by skeletal muscle peptidases. The results show that SP is degraded not only by NEP-24.11, but also sequentially by dipeptidyl(amino)peptidase IV (DAP IV; EC 3.4.14.5)/APN. NKA is unaffected by DAP IV but is metabolized by NEP-24.11 and APN. NEP-24.11 was inhibited by phosphoramidon (IC₅₀ = 80 nM), thiorphan and ZINCOV, DAP IV by diprotin A (IC₅₀ = 8 μM), and APN by amastatin (IC₅₀ = 50 nM) and bestatin (IC₅₀ = 100 μM). Skeletal muscle myocyte and fibroblast metabolism of SP and NKA may regulate local skeletal muscle vascular and extravascular functions including SP- and NKA-mediated nerve-induced vasodilation. Inhibition of both NEP-24.11 and DAP IV/APN may increase skeletal muscle blood flow and decrease peripheral vascular resistance via potentiation of local neurokinin levels.