Collagen synthesis and types I, III, IV, and VI collagens in an animal model of disc degeneration

STUDY DESIGN

The present study sought to elucidate the changes that occur in collagen chemistry in the early phases of disc degeneration.

OBJECTIVE

To monitor the healing process of the injured anulus fibrosus and the secondary degenerative reactions in the nucleus pulposus.

SUMMARY OF BACKGROUND DATA

Despite the importance of collagen chemistry under pathologic conditions in the intervertebral disc, knowledge of this aspect is very limited.

METHODS

Fourteen pigs were stabbed with a scalpel blade in the anterior part of the anulus fibrosus of a lumbar disc. The animals were killed 2 weeks to 5 months after injury. The activities of prolyl 4-hydroxylase and galactosylhydroxylysyl glucosyltransferase, the total collagen content, and staining patterns for Types I, III, IV, and VI collagens were analyzed from different parts of the disc.

RESULTS

The most active phase of the healing process, assessed from the activities of enzymes involved in collagen biosynthesis, took place during the first month postoperatively. The anular lesion was found to cicatrize through formation of disorganized granulation tissue in which Type I, III, and, IV collagens were deposited. In the nucleus pulposus, activities of prolyl 4-hydroxylase and galactosylhydroxylysyl glucosyltransferase and total collagen content increased, and the originally rounded cells became more elongated, resembling fibroblasts.

CONCLUSIONS

The results of this study suggest that the altered composition of collagens observed in the degenerate porcine nucleus pulposus results from changes in cell phenotype: Notochondral cells were replaced by fibroblast-like cells. It is likely that trauma to the anulus fibrosus can initiate a progressive degenerative process in the disc tissue.

Further study on the spontaneous partial folding of chicken heart apocytochrome c

It has been previously reported (Biochem. Mol. Biol. Int., 30(5), 867-876, 1993) that chicken heart apocytochrome c has stronger tendency to fold spontaneously in aqueous solution than those from other species, and the relevance of its folding state with its ability to penetrate across the lipid bilayers has also been studied. In the present paper, the spontaneous folding characteristics of chicken heart apocytochrome c was further examined by the studies of Fourier-transform infrared spectra, the properties of intrinsic tryptophan fluorescence, and the measurements of hydrophobicity. In addition, it was also demonstrated that the partially-folded apocytochrome c is easily to be aggregated and hence relatively incompetent for translocation across the phospholipid bilayers.

8-Hydroxylation of guanine bases in kidney and liver DNA of hamsters treated with estradiol: role of free radicals in estrogen-induced carcinogenesis

The chronic administration of estradiol induces a high incidence (80-100%) of renal tumors in male Syrian hamsters. As part of our examination of a mechanism of carcinogenesis by free radicals generated during redox cycling of catecholestrogen metabolites, we assayed levels of 8-hydroxy-2'-deoxyguanosine (8-OHdGua), a marker product of hydroxy radical interaction with DNA, in livers and kidneys of hamsters treated with estradiol. Injections of 50 and 100 mg/kg estradiol doubled renal 8-OHdGua levels over controls [10.0 +/- 0.1 (SD) and 5.4 +/- 0.4 8-OHdGua/10(5) dGua, respectively] and raised hepatic 8-OHdGua levels almost 4-fold over control values, respectively. These changes were observed in kidney 4 h and in liver 1 or 2 h after treatment of hamsters with estradiol. Estradiol implants administered to hamsters for 3 days raised renal levels of 8-OHdGua by 50% over control values. Six days after 17 beta-estradiol implantation, 8-OHdGua levels returned to near-normal values. Liver DNA was not affected by estradiol implants. These data support a mechanism of estrogen-induced carcinogenesis by free radicals generated via redox cycling of catecholestrogen metabolites.

Electrospray ionization mass spectroscopic analysis of human erythrocyte plasma membrane phospholipids

Electrospray ionization mass spectrometry (ESI-MS) was utilized for the structural determination and quantitative analysis of individual phospholipid molecular species from subpicomole amounts of human erythrocyte plasma membrane phospholipids. The sensitivity of ESI-MS was 2-3 orders of magnitude greater than that achievable with fast-atom bombardment mass spectrometry (FAB-MS). Phospholipid structure determination and quantitative analysis with ESI-MS can be performed directly from chloroform extracts of biologic samples, obviating the need for prior chromatographic separation of phospholipid classes which has been necessary in FAB-MS phospholipid analyses. Furthermore, ESI-MS is uncomplicated by differential fragmentation of molecular ions and idiosyncratic surface desorption, allowing the quantitation of phospholipids with coefficients of determination (r2) > 0.99 and accuracies > 95%. More than 50 human erythrocyte plasma membrane phospholipid constituents were identified by direct ESI-MS analysis of chloroform extracts of plasma membranes derived from the equivalent of < 1 microliter of whole blood. The major ethanolamine glycerophospholipid subclass in erythrocyte plasma membranes was plasmenylethanolamine that was highly enriched in polyunsaturated fatty acids at the sn-2 position. Collectively, these results demonstrate that ESI-MS of phospholipids is an enabling strategy for the direct structural determination and quantitative analysis of subpicomole amounts of phospholipids from biologic samples.

Developmental changes in the distribution of pro-opiomelanocortin and prolactin mRNA in the pituitary of the ovine fetus and lamb

Ontogenic changes in pituitary pro-opiomelanocortin (POMC) mRNA and prolactin (PRL) mRNA were examined during gestation and early neonatal life using in situ hybridization histochemistry. Pituitaries were harvested from fetuses at days 60-80, 100-120, 135-140 and 142-143 of gestation and at term, and from lambs at days 1-7 and 30-60 of age and adults. POMC mRNA, present by day 60, rose during mid- and late gestation. Concurrently there was a change in corticotroph distribution, resulting in a relatively greater quantity of POMC mRNA at the base of the pars distalis. At term, there was a significant (P < 0.05) further elevation of POMC mRNA. POMC mRNA levels remained high in the newborn lamb but decreased in the adult. Cells in the pars intermedia expressed large amounts of POMC mRNA early in fetal life and this pattern persisted throughout gestation and into the neonatal period. Changes in the expression of the POMC gene correlated closely with the presence of immunoreactive (ir)ACTH in the pituitary; in fetuses the proportion of irACTH-positive cells rose to 10% of pars distalis cells by day 100 and did not change significantly thereafter. The lactotrophs contained PRL mRNA by day 60, and the quantity increased towards parturition (P < 0.05). PRL mRNA subsequently decreased in the neonate, but rose as the lamb matured. These results indicate that in the fetal pituitary: (1) the POMC gene is highly expressed during gestation in both the pars distalis and the pars intermedia, (2) changes in the amounts of POMC mRNA and PRL mRNA in the pars distalis correlate with the distribution of irACTH and irPRL respectively, and (3) POMC mRNA is distributed primarily in the inferior aspect of the pars distalis, and in this region its quantity is highest immediately prior to parturition.

Regulation of the formation of the major diethylstilbestrol-DNA adduct and some evidence of its structure

Diethylstilbestrol (DES) induces kidney tumors in hamsters. In previous studies, DES has been shown by 32P-post-labeling analysis to bind covalently to DNA in vivo and in vitro and DES-DNA adduct formation has been suggested to play a key role in DES-induced carcinogenicity. In this study, we have examined the influence of the dose of DES, age of animals and organ specificity on adduct formation in hamsters. In addition, we examined the characteristics of DES-DNA adduct formation in vitro and the structure of the major adduct. DES-DNA adducts were detected in liver and kidney of hamsters treated with at least 20 mg/kg DES. Adduct concentrations were higher at higher doses or in older compared to younger animals. The covalent binding of DES to DNA catalyzed by hamster liver microsomes required cumene hydroperoxide as cofactor, whereas with NADPH, adducts were barely detectable, presumably because the reactive metabolic intermediate DES quinone was reduced to DES. The major DES-DNA adduct formed in vitro was purified by semipreparative and analytical high pressure liquid chromatography. It is concluded that DES-DNA adducts are formed from DES quinone at very low rates in vitro and occur at low levels in vivo, even when hamsters receive very large doses of DES. The dependence of DES-DNA adduct concentrations in vitro on organic hydroperoxide cofactors required for cytochrome P450-mediated DES quinone formation indicates that stilbene-DNA adduction may occur only under conditions of oxidative stress.

The effect of putative insulin-like substances released by the motor nerve on glucose transport in perfused rat muscle

Motor nerves have been claimed to contain and release immunoreactive insulin. We studied whether release of insulin or other non-acetylcholine substances is important for (1) the increase in glucose transport normally seen during motor nerve activated contraction, and (2) the increase in insulin sensitivity induced by contractions. Ad 1:Rat hindquarters were perfused and one sciatic nerve was stimulated during motor nerve end plate blockade (Pancuronium bromide, 33 micrograms ml-1). Muscle glucose transport (3-O-[14C]-methylglucose (3-O-MG) uptake, 3 mM) was identical (P > 0.05) in stimulated compared with nonstimulated white gastrocnemius, red gastrocnemius and soleus muscle. This was also true when, prior to end plate blockade, muscles had been stimulated to contract to increase insulin sensitivity. No immunoreactive insulin was found in venous perfusate. Ad 2: Rats had both sciatic nerves cut. One week later hindquarters were perfused and calf muscles of one leg were directly stimulated to contract. Subsequently, 3-O-MG uptake in muscle was determined with and without submaximal insulin (100 microU ml-1). In contrast to previous findings in innervated muscle, responses to insulin were identical (P > 0.05) with and without prior contractions.

CONCLUSIONS

The increase in muscle glucose transport normally seen in response to motor nerve stimulation is related to the contraction process and not even partly mediated by release of insulin-like substances from the nerve. In contrast, release of a non-acetylcholine substance from the motor nerve may be involved in the exercise induced increase in insulin sensitivity.

DNA single-strand breaks in kidneys of Syrian hamsters treated with steroidal estrogens: hormone-induced free radical damage preceding renal malignancy

The chronic administration of estradiol by subcutaneous (s.c.) implantation into male Syrian hamsters induces kidney tumors. Free radicals generated by redox cycling between catecholestrogens and their quinones have been proposed to damage DNA and to thus mediate renal hormone-induced carcinogenesis. As part of an examination of this postulate, we assayed by a filter elution technique DNA single-strand breaks in livers and kidneys of male hamsters treated with estrogen by single intraperitoneal (i.p.) injection, by s.c. implant or by continuous infusion and compared values to those in untreated controls. The DNAs of hamster liver and kidney were not affected by one i.p. injection of 5, 15 or 150 mg/kg estradiol. However, treatment of hamsters with one 25 mg estradiol implant/animal for 2 weeks elevated by 10% the levels of DNA single-strand breaks in kidney, but only to a minor extent in liver, which is not a target of estrogen-induced carcinogenesis. An infusion of 250 micrograms/day/animal of estradiol or 4-hydroxyestradiol for one week by osmotic pumps into hamsters resulted in a comparable increase of single-strand breaks in kidney DNA, whereas 2-hydroxyestradiol under these conditions had a negligible effect. It is concluded that the induction of DNA single-strand breakage by either estradiol or 4-hydroxyestradiol in hamster kidney supports a mechanism of estrogen-induced carcinogenesis by free radical generation via redox cycling between 4-hydroxyestradiol and its corresponding quinone.

An obligatory role for nitric oxide in autonomic control of mammalian heart rate

Cholinergic modulation of heart rate in isolated spontaneously beating single cells from the rabbit sino-atrial node was investigated by measuring transmembrane ionic currents using the nystatin-perforated patch whole-cell voltage-clamp technique. Carbamylcholine (CCh), a stable analogue of acetylcholine (ACh), significantly inhibited L-type calcium currents (Ica(L) which had been augmented by beta-adrenergic stimulation. In addition, CCh activated a potassium outward current (IK(ACh)). Both effects were blocked by atropine. The possible involvement of nitric oxide (NO) in these responses was evaluated by inhibiting NO synthesis. In the presence of NG-monomethyl-L-arginine (L-NMMA, 100 microM) or nitro-L-arginine methyl ester (L-NAME, 1 mM), two specific inhibitors of nitric oxide synthase (NOS), CCh no longer inhibited ICa(L). IK(ACh) could still be activated. Co-incubation of cells in L-NAME or in L-NMMA with arginine (the endogenous substrate of NOS) restored the CCh-induced attenuation of ICa(L), indicating that L-NAME or L-NMMA did not interfere directly with the muscarinic action of CCh on ICa(L). Effects of the NO-releasing agent molsidomine (SIN-1) on CCh-induced changes in ICa(L) were also investigated. After ICa(L) had been augmented by beta-adrenergic stimulation, SIN-1 (0.1 mM) inhibited ICa(L); however, SIN-1 had no further inhibitory effect after a maximal CCh concentration had been applied. These findings suggest that NO generation is an obligatory process in cholinergic inhibition of ICa(L) in mammalian cardiac pacemaker tissue.

Relaxin increases heart rate by modulating calcium current in cardiac pacemaker cells

Relaxin (RLX), a reproductive hormone of the insulin family, increases heart rate in experimental animals. The cellular and ionic mechanisms responsible for this positive chronotropic effect remain unknown. We have investigated the actions of RLX on the action potential and underlying transmembrane ionic currents in single sinoatrial node cells of the rabbit heart under whole-cell voltage-clamp conditions, using both nystatin-perforated-patch and membrane-ruptured techniques. In this preparation RLX (0.8 to 80 nmol/L) caused reversible increases in the rate of spontaneous action potentials and a dose-dependent increase in the L-type calcium current, ICa(L). The best-fit Langmuir relation for the augmentation of ICa(L) yielded a threshold concentration of 1 nmol/L and a KD of 14 nmol/L. These effects of RLX appear to be mediated by increases in intracellular cyclic AMP (cAMP), since RLX was without effect after application of (1) the beta-adrenergic agonist isoprenaline (1 mumol/L) or (2) superfusion of the intracellular second messenger cAMP (100 mumol/L) or 8-Br-cAMP (100 to 200 mumol/L). Internal dialysis with an inhibitor of cAMP-dependent protein kinase (PKI, 7 mumol/L) abolished the effects of RLX. These results provide the first electrophysiological evidence that RLX modulates heart rate and contractility by increasing ICa(L) and suggest that the biochemical mechanism involves the formation of cAMP and activation of cAMP-dependent protein kinase.

Expression of taurine transporter and its regulation by diet in Xenopus laevis oocytes following injection of rat kidney cortex mRNA

NaCl-dependent taurine transport adapts to changes in the dietary intake of sulfur amino acids. The renal adaptive response is expressed by enhanced NaCl-dependent taurine cotransport by brush border membrane vesicles after a low taurine diet and reduced transport after a high taurine diet as compared to a normal taurine diet. In order to determine if this adaptive regulation is dependent on new protein synthesis, the Xenopus laevis oocyte expression system was utilized to define the translational regulation of taurine transporter activity. Poly(A)+ RNA was isolated from kidney cortex of Sprague Dawley rats fed either a low, normal or high taurine diet for 28 days. Injection of poly(A)+ RNA resulted in a time- and dose-dependent increase in NaCl-taurine co-transport. Taurine uptake was stimulated about 2-10-fold after injection of poly(A)+ RNA (10-40 ng) as compared to H2O-injected oocytes. Taurine uptake by oocytes was sodium- and anion-dependent (Cl- > Br- > SCN- > I-). The Km and Vmax of the taurine transporter were 22.5 microM and 8.35 pmol/h/oocyte respectively, similar to the Km of 17.0 microM found in rat brush border membrane vesicles. Because the adaptive response involves an augmented or reduced Vmax of the transporter, taurine uptake by oocytes injected with poly(A)+ RNA from rats fed each diet was examined. Poly(A)+ RNA from rats fed a low taurine diet elicited twice the taurine uptake elicited from rats fed a normal taurine diet and more than three times the uptake from high taurine-fed rats. Northern blot analysis after hybridization with an RNA probe for the taurine transporter cDNA from MDCK cells (obtained from Dr. Uchida) indicated that the molecular size of taurine transporter mRNA is about 1.9 kb and is regulated by diet. Expression of taurine transporter by the oocytes injected with 30 ng of capped transcript from pNCT was significantly reduced by taurine in the medium. In conclusion, taurine uptake by oocytes after injection of mRNA is similar to brush border membrane vesicles taurine transport. The long-term adaptive response is regulated at the level of mRNA, and the short-term adaptive response is regulated at the level of protein synthesis or secretion. We speculate that the renal adaptive response to altered dietary sulfur amino acid intake is both transcriptionally and translationally regulated.

Collagens in the injured porcine intervertebral disc

Spinal pain often is thought to be due to degeneration and mechanical failure of the intervertebral disc. Since the mechanical strength of the tissue depends on collagen fibers, the present study was designed to investigate the reactions in collagen metabolism after an experimentally induced disc injury. Five domestic pigs underwent an incision in the anterior part of the annulus fibrosus of disc L4-L5 through a retroperitoneal approach. The animals were killed 3 months postoperatively, and the injured discs and intact discs (controls) from different animals were removed for chemical analysis. Slices were cut from seven different parts across the disc. The concentration of total collagen (hydroxyproline [Hyp]), the activities of the two key enzymes in collagen biosynthesis (prolyl 4-hydroxylase [PH] and galactosylhydroxylysyl glucosyltransferase [GGT]), and the concentration of mature collagen crosslinks (hydroxypyridinium [HP]) were determined. In all experimental discs, the morphology had changed considerably: the nucleus pulposus was small, fibrous, and yellowish. The annular lamellar structure was partially destroyed and had been replaced by granulation tissue in the region of the injury. Large osteophytes had formed at the ventral edges of the vertebral bodies. In the nucleus pulposus, the Hyp concentration and the activities of PH and GGT were significantly increased, whereas the water content had decreased. The concentration of HP crosslinks was decreased in the anterior annulus fibrosus.

Dynamics of binary mixtures of plasmenylcholine/arachidonic acid and phosphatidylcholine/arachidonic acid--a study using fluorescence and NMR spectroscopy

Arachidonic acid is selectively released during signal transduction in many cell types. To examine the effects of physiologically relevant amounts of arachidonic acid on membrane bilayers, alterations in membrane dynamics induced by arachidonic acid were investigated utilizing fluorescence and nuclear magnetic resonance spectroscopy. We demonstrate that decreases in the fluorescence steady-state anisotropy of diphenylhexatriene are induced by incorporation of physiologically relevant amounts (i.e., 5 mol%) of arachidonic acid into either phosphatidylcholine or plasmenylcholine membrane bilayers. Furthermore, examination of the motional dynamics of the bis-allylic protons in arachidonic acid by analyses of their spin-spin relaxation times demonstrated that these protons are more restrained when arachidonic acid is present as a substitutional impurity in plasmenylcholine vesicles than in phosphatidylcholine vesicles. Collectively, these results demonstrate that arachidonic acid, when present in physiologically relevant mole fractions, can modify the molecular dynamics of biological membranes and that the motional dynamics of arachidonic acid in membrane bilayers is influenced by the type of covalent linkage present in the proximal portion of the sn-1 aliphatic chain in host bilayer matrices.

Interleukin-6 (IL-6) functions as an autocrine growth factor in cervical carcinomas in vitro

Many factors have been implicated in the etiology of cervical neoplasia, with human papilloma virus being the latest in a long line of agents that may on their own or in combination exert various initiating and promoting effects on cervical cells, resulting in their transformation. However, for such altered cells to become invasive, it is clear that they must undergo alterations in their rate of turnover, state of differentiation, and motility. We have investigated the production of the multifunctional cytokine interleukin-6 (IL-6) by five new cervical carcinoma cell lines (XH1, EH2, DE3, JE6, and SM7) and the commercially available CaSki cell line, and have studied the effects of this cytokine on the growth of the cells in vitro. All the cell lines produce biologically active IL-6 in amounts varying between 0.35 to 2.0 ng/ml. In the presence of goat anti-sera to IL-6 all the tumor cell lines showed inhibition of growth. IL-6 acts as an autocrine growth factor for in vitro cervical tumor cell growth.

Microsomal hydroxylation of 2- and 4-fluoroestradiol to catechol metabolites and their conversion to methyl ethers: catechol estrogens as possible mediators of hormonal carcinogenesis

In male Syrian hamsters, an animal model for estradiol-induced carcinogenesis, 2-fluoroestradiol was not carcinogenic, whereas 4-fluoroestradiol induced kidney tumors after a prolonged latency period, compared with estradiol (100% tumor incidence), when the compounds were administered to hamsters in hormonally equipotent doses. Catechol estrogen metabolites have previously been postulated to mediate this estrogen-induced kidney carcinogenesis. To examine this proposed mechanism of tumor induction by estrogens, we investigated the conversion of 2- and 4-fluoroestradiol to catechol metabolites by kidney and liver microsomes of hamsters and the further conversion to methyl ethers by catechol-O-methyltransferase, and we compared the values with those obtained with nonfluorinated estrogens as substrates. The rates of conversion of 2-fluoroestradiol to 2-hydroxyestradiol and 2-fluoro-4-hydroxyestradiol by hepatic microsomes were 30-50% lower than corresponding rates with estradiol as substrate. With renal microsomes the rate of 4-hydroxylation was 10 times faster than that of estradiol, whereas 2-hydroxylation was at best marginal. With 4-fluoroestradiol as substrate the rate of 2-hydroxylation by hepatic microsomes was enhanced 5-fold, compared with values for estradiol, but 4-hydroxyestradiol formation was almost eliminated. In contrast, the conversion of this substrate to 4-fluoro-2-hydroxyestradiol by kidney microsomes occurred at a rate 15 times faster than 2-hydroxylation of estradiol, whereas 4-hydroxyestradiol formation proceeded at a rate of 315 pmol/mg of protein/min. Except for the decrease in both 2- and 4-hydroxylation of 2-fluoroestradiol by liver microsomes, fluorine substitution of estrogenic phenols enhanced microsome-mediated aromatic hydroxylation at sites unoccupied by substituents. At pH 7.5, the highest rates of catechol-O-methyltransferase-mediated methylation were observed with the catechol metabolites of 2-fluoroestradiol, 2-fluoro-4-hydroxyestradiol and 2-hydroxyestradiol (3780 and 2960 pmol/mg of protein/min, respectively). Lower rates were found with those of 4-fluoroestradiol, 4-fluoro-2-hydroxyestradiol and 4-hydroxyestradiol (1670 and 470 pmol/mg of protein/min, respectively). These data are consistent with the postulate that catechol metabolites of estrogens are reactive intermediates in estrogen-induced carcinogenesis. For the noncarcinogenic 2-fluoroestradiol, a high metabolic flux was observed through a pathway of renal 2-fluoro-4-hydroxyestradiol formation and further conversion to methyl ethers. This flux likely results in low steady state concentrations of catechol metabolites in kidneys of hamsters treated with this modified estrogen and therefore in its lack of carcinogenic activity. In contrast, the carcinogenic activity of 4-fluoroestradiol is consistent with its rapid conversion in the kidney to 2- and 4-hydroxylated metabolites and a less rapid methylation of these catechols.

Rat and human pancreatic islet cells contain a calcium ion independent phospholipase A2 activity selective for hydrolysis of arachidonate which is stimulated by adenosine triphosphate and is specifically localized to islet beta-cells

The recent demonstration that myocardial Ca(2+)-independent phospholipase A2 exists as a complex of catalytic and regulatory polypeptides that is modulated by ATP has suggested a novel mechanisms through which alterations in glycolytic flux can be coupled to the generation of eicosanoids which facilitate insulin secretion. To determine the potential relevance of this mechanism, we examined the kinetic characteristics, substrate specificities, and cellular locus of phospholipase A2 activity in pancreatic islets. Rat pancreatic islets contain a Ca(2+)-independent phospholipase A2 activity which is optimal at physiologic pH, preferentially hydrolyzes phospholipid substrates containing a vinyl ether linkage at the sn-1 position, and prefers arachidonic acid compared to oleic acid in the sn-2 position. Rat islet Ca(2+)-independent phospholipase A2 activity is inhibited by the mechanism-based inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one and is stimulated by ATP. Purification of beta-cells from dispersed pancreatic islet cells by fluorescence-activated cell sorting demonstrated that beta-cells (but not non-beta-cells) contain Ca(2+)-independent, ATP-stimulated phospholipase A2 activity. Remarkably, clonal RIN-m5f insulinoma cells, which possess a defect in glucose-induced insulin secretion, contain a Ca(2+)-independent phospholipase A2 which is not modulated by alterations in ATP concentration. Collectively, these results and those of an accompanying paper [Ramanadham et al. (1993) Biochemistry (following paper in this issue)] implicate Ca(2+)-independent phospholipase A2 as a putative glucose sensor which can couple alterations in glycolytic metabolism to the generation of biologically active eicosanoids and thereby facilitate glucose-induced insulin secretion.

Inhibition of arachidonate release by secretagogue-stimulated pancreatic islets suppresses both insulin secretion and the rise in beta-cell cytosolic calcium ion concentration

Fuel secretagogues induce hydrolysis of esterified arachidonic acid from pancreatic islet cell phospholipids and accumulation of nonesterified arachidonate at concentrations up to 35 microM. Exogenous arachidonate (5-30 microM) amplifies depolarization-induced insulin secretion from islets. Fuel secretagogue-induced hydrolysis of arachidonate from islet phospholipids occurs in Ca(2+)-free medium, suggesting the possible involvement of a Ca(2+)-independent phospholipase. In the companion paper [Gross et al. (1993) Biochemistry (preceding paper in this issue)], we demonstrated that the major islet phospholipase A2 is Ca(2+)-independent, ATP-stimulated, and inhibited by the haloenol lactone suicide substrate (HELSS) (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one. Here we demonstrate that HELSS suppressed both release of the arachidonate metabolite prostaglandin E2 and insulin secretion from islets stimulated with D-glucose and the muscarinic agonist carbachol. Both prostaglandin E2 release and insulin secretion were suppressed with similar concentration profiles and time courses. Islet oxidation of [14C]-glucose to [14C]CO2, activities of islet lactate dehydrogenase and alanine and aspartate aminotransferases, and carbachol-induced inositol phosphate accumulation in islets were all unaffected by HELSS. Depolarization of isolated beta-cells with 40 mM KCl induced a rise in cytosolic [Ca2+] that was also unaffected by HELSS. In contrast, the 17 mM D-glucose-induced rise in beta-cell [Ca2+] was inhibited by HELSS in a concentration-dependent manner, but that induced by exogenous arachidonate (15 microM) was not. These results suggest that fuel secretagogues activate the islet Ca(2+)-independent phospholipase A2, resulting in release of nonesterified arachidonate, which facilitates Ca2+ entry into beta-cells and promotes insulin secretion.

Cytoblock preparations for examination of cervical and other cells

There are a number of antibodies which may be of value in the investigation of cervical smears, effusion, and cells grown in monolayer culture. The Shandon Cytoblock method was used to prepare discs of such cells suitable both for diagnosis and for a variety of other techniques.

Epimeric (20R,20S)-Verazine Isolated from Veratrum maackii: Two-Dimensional NMR Studies and Total Assignment of 1H- and 13C-Resonances

(13)C-NMR evidence shows that verazine [(25 S)-iminocholesta-5,22( N)-diene-3beta-ol] isolated from the Chinese plant VERATRUM MAACKII (Melanthiaceae) consists of a 20 R/20 S mixture of epimers. The determination of the configurations at the chiral epimeric center and of the conformation of the 17beta-side chain is based on the total assignment of the (13)C- and (1)H-NMR resonances. This goal was achieved by the extensive use of homo- and heteronuclear shift correlation and two-dimensional NOE spectroscopy methods at high magnetic field.

Ionic mechanisms of transient inward current in the absence of Na(+)-Ca2+ exchange in rabbit cardiac Purkinje fibres

1. Membrane currents were measured with a two-microelectrode technique in voltage clamped rabbit cardiac Purkinje fibres under conditions known to cause intracellular calcium overload and to eliminate or minimize Na(+)-Ca2+ exchange. 2. Increasing [Ca2+]o from 2.5 to 5 mM or above and substituting external sodium with either sucrose, choline or Li+ induced an oscillatory transient inward current (TI) which peaked 200-300 ms after repolarization from a previous depolarizing pulse. The TI quickly disappeared upon return to normal Tyrode solution. Both the rate and configuration of action potentials of Purkinje fibres also returned to control upon return to Tyrode solution after 30 min of high Ca2+ exposure, if the Ca2+ concentration was 30 mM or less. 3. The TI in Na(+)-free solution was Ca2+ dependent. Either zero or low (2.5 mM) [Ca2+]o, or replacement of [Ca2+]o by BaCl prevented induction of the TI current upon repolarization from a previous depolarizing pulse. 4. In the presence of 30 mM-CaCl2 and with choline chloride as the substitute for NaCl, TI had a distinct reversal potential (Erev) of -25 mV. The time-to-peak TI, either inward or outward, did not shift significantly with change in voltage. Both inward and outward TI were simultaneously abolished by exposure to 1 microM-ryanodine, suggesting they were both activated by transient release of Ca2+ from the sarcoplasmic reticulum. The occurrence of TI in the absence of [Na+]o is not compatible with an electrogenic Na(+)-Ca2+ exchange mechanism. The existence of a clear-cut reversal potential suggests that an ionic channel may be responsible for the TI under these conditions. 5. Both the magnitude of peak TI and the Erev were affected by changes of CaCl2 concentration. (i) Under steady-state conditions, peak inward TI was significantly increased when the [Ca2+]o was elevated from 5 to 15 mM. The peak TI in the outward direction was significantly increased when [Ca2+]o was elevated from 15 to 30 mM; however, the difference in peak inward TI at 15 and 30 mM [Ca2+]o was small. (ii) Clear-cut reversals of TI were found at Ca2+ concentrations of 10 mM (Erev = -19.5 mV) or greater, and elevation of [Ca2+]o to 20, 30, 50 and 105 mM shifted the Erev to more negative potentials. (iii) In the presence of 5 mM [Ca2+]o the inward TI declined to zero at about -30 mV, and test voltages between -55 and +5 mV failed to reveal a distinct outward TI.(ABSTRACT TRUNCATED AT 400 WORDS)

TDM35--a new monoclonal antibody to the XH1 cervical carcinoma cell line. Characterization and immunoperoxidase localization in benign and malignant tissues

The murine monoclonal IgG1 kappa antibody TDM35 was raised against the cervical carcinoma cell line XH1. The antibody recognizes 18.5-66 kDa NCA-like glycoproteins and immunostains a variety of formalin-fixed, paraffin-embedded normal, benign, and malignant tissues. It is of value in the diagnosis of carcinoma of the exocrine pancreas and it identifies foci of squamous and glandular differentiation in other tumours. TDM35 should form a useful addition to a panel of antibodies for the evaluation of epithelial lesions.

Nonmonotonic alterations in the fluorescence anisotropy of polar head group labeled fluorophores during the lamellar to hexagonal phase transition of phospholipids

The temperature dependence of the fluorescence anisotropy of polar head group labeled fluorophores (i.e., N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)dipalmitoyl-L- alpha-phosphatidylethanolamine or N-(lissamine rhodamine B sulfonyl)dipalmitoyl-L-alpha-phosphatidylethanol- amine) incorporated into multiple phosphatidylethanolamine molecular species was parabolic, possessing minima (dr/dT = 0) that precisely correlated with the respective lamellar (L alpha) to hexagonal (HII) phase transition temperature of each species. The parabolic alterations in the thermotropic behavior of these fluorophores were due to increased motional constraints in the polar head group region during heating (dr/dT greater than 0), because significant alterations in the fluorescence lifetimes of these probes during the phase transition did not occur. The sensitivity inherent in identification of peak minima was exploited to determine the lamellar to hexagonal phase transition temperatures of several homogeneous molecular species of plasmenylethanolamine (e.g., the transition temperature of 1-O-(Z)-hexadec-1'-enyl-2-octadec-9'- enoyl-sn-glycero-3-phosphoethanolamine was 28 degrees C). Experiments using ethanolamine glycerophospholipids containing either an ester or a vinyl ether linkage at the sn-1 position demonstrated that introduction of the vinyl ether constituent increased the propensity of these species to assume the hexagonal phase. Collectively, these results identify and substantiate a new technique for the characterization of the lamellar to hexagonal phase transition in phospholipids that requires only small amounts of phospholipids present in dilute membrane suspensions.

Differential molecular dynamics and transmembrane fluidity gradients in canine myocardial sarcolemma and sarcoplasmic reticulum

The molecular dynamics of highly purified preparations of canine myocardial sarcolemma (SL) and sarcoplasmic reticulum (SR) were quantified by electron spin resonance spectroscopy (ESR). Canine myocardial SL and SR have substantially different motional regimes in their membrane interiors as demonstrated by alterations in the relative peak height ratios, peak widths and peak splittings in ESR spectra of 16-doxylstearate incorporated into SL and SR. Quantification of the apparent order parameters (S) of 16-doxylstearate in SL and SR by analyses of ESR spectra demonstrated that the interior of the SL membrane was substantially more immobilized than the interior of the SR membrane (e.g. S = 0.168 +/- 0.002 for SL and S = 0.128 +/- 0.003 for SR). In contrast, only modest differences in membrane dynamics near the hydrophobic-hydrophilic interface were present in SL and SR as ascertained by ESR spectra of the probe 5-doxylstearate incorporated into these membranes. Myocardial sarcolemma contained heretofore unsuspected amounts of cholesterol (1.4 +/- 0.1 mumol cholesterol/mg protein) while sarcoplasmic reticulum contained only small amounts of cholesterol (0.17 +/- 0.06 mumol cholesterol/mg protein). Model systems employing binary mixtures of plasmenylcholine/cholesterol and phosphatidylcholine/cholesterol demonstrated that the observed alterations in molecular dynamics were due, in large part, to the differential cholesterol content in these two subcellular membrane compartments. Taken together, these results demonstrate that these two functionally distinct myocardial subcellular membranes have markedly disparate molecular dynamics and transmembrane fluidity gradients which may facilitate their performance of specific functional roles during excitation-contraction coupling in myocardium.