Oral anticoagulant treatment in a medical care district--a descriptive study

OBJECTIVE

To describe how oral anticoagulant therapy is performed in a defined catchment area in order to improve the quality of care.

DESIGN

Two study periods of 8 weeks were compared with reference to monitoring sites, i.e. hospital departments and primary health care centres.

SETTING

The health care district of Umeå in northern Sweden, with 125,300 inhabitants.

PARTICIPANTS

Patients on oral anticoagulant therapy at the department of Internal Medicine, Umeå University Hospital, in 1987 (n = 243) were compared with all patients treated in 1990 at health centres (n = 175) and at the department of Internal Medicine (n = 290) in the Umeå district.

MAIN OUTCOME MEASURES

The prevalence of treatment failures and complications was calculated per patient year, as well as the relative frequencies of patients within treatment recommendations.

RESULTS

80-83% of the patients were within treatment recommendations. Treatment failures were 3.6% of hospital patients, and 2.6% of primary care patients. Corresponding figures for bleeding complications were 8.9% and 5.1%, respectively. The differences are partly explained by differences in the studied groups, e.g. age, indications for treatment, and concomitant diseases.

PU box-binding transcription factors and a POU domain protein cooperate in the Epstein-Barr virus (EBV) nuclear antigen 2-induced transactivation of the EBV latent membrane protein 1 promoter

Expression of the Epstein-Barr virus (EBV) latent membrane protein (LMP1) is regulated by virus- and host cell-specific factors. The EBV nuclear antigen 2 (EBNA2) has been shown to transactivate a number of viral and cellular gene promoters including the promoter for the LMP1 gene. EBNA2 is targeted to at least some of these promoters by interacting with a cellular DNA binding protein, RBP-J kappa. In the present report we confirm and extend our previous observation that the LMP1 promoter can be activated by EBNA2 in the absence of the RBP-J kappa-binding sequence in the LMP1 promoter regulatory region (LRS). We show that two distinct LRS regions, -106 to +40 and -176 to -136, contribute to EBNA2 responsiveness. Site-directed mutagenesis analysis of the upstream -176/-136 EBNA2 responsive element revealed that two critical cis-acting elements are required for full promoter function. These same elements analysed by electrophoretic mobility shift assays define two binding sites recognized by nuclear factors derived from B cells. An octamer-like sequence (-147 to -139) contained overlapping binding sites for an unidentified transcriptional repressor on the one hand and a factor(s) belonging to the POU domain family but distinct from Oct-1 and Oct-2 on the other. An adjacent purine tract (-171 to -155) held a PU.1 binding site, which was also recognized by a related factor. The results suggest that the POU domain protein and either of two PU box-binding factors bind simultaneously to LRS, creating a ternary complex that might be in part responsible for mediating the transactivation of the LMP1 promoter by EBNA2. There were no qualitative differences between EBV-negative and EBV-positive cells with regard to transcription factor binding to the octamer-like sequence and the PU.1 recognition site, as revealed by electrophoretic mobility shift assays.

Redrawing compartmental boundaries in the exocytic pathway

Compartments can be defined both morphologically as well as biochemically. The former relies on a direct visualisation of membrane boundaries and the latter by the characterisation of enzymatic functions taking place within the compartment. The combination of morphology and biochemistry has led to the identification of several compartments within the exocytic pathway, each assumed to carry out independent functions in a logical succession [Palade, G. (1975) Science 189, 347-358]. However, recent findings show that resident enzymes are confined to not one but at least two adjacent compartments suggesting that morphological and biochemical definitions do not coincide. We will here discuss these findings and propose a model to explain how compartments are organised and maintained along the exocytic pathway.

Oxygen reaction and proton uptake in helix VIII mutants of cytochrome bo3

The oxygen reaction of wild-type and helix VIII mutants of cytochrome bo3 from Escherichia coli, and the associated proton uptake during this reaction, has been studied using flash photolysis of the CO complex of the reduced protein after rapid mixing with oxygen. We have focused on mutations in the transmembrane helix VIII where protonatable residues have been exchanged, and mainly on the inactive mutants (i.e., T352A, T359A, and K362L, -M, and -Q). The kinetics for electron transfer during oxidation for the mutants are similar to the wild-type; two rate constants of 3.2 x 10(4) and 3.4 x 10(3) s-1 (at 1 mM oxygen) are detected. Proton uptake is observed for wild-type as well as for the mutant enzymes, but the mutations within helix VIII have affected the rate of proton uptake; it is significantly accelerated in the mutants. These results show that none of the protonatable residues in helix VIII are required in the reaction between the fully reduced cytochrome bo3 and oxygen. We have also studied electron redistribution after photolysis of CO from the mixed-valence compound; we found three kinetic components for wild-type and the mutants T352A and T359A, but for K362M only the first and third components are observed, with amplitudes that are lower than those for the corresponding components in the wild-type enzyme, suggesting that the characteristics of internal electron transfer in the K362M mutant are different from those of the wild-type enzyme.

Mapping the distribution of Golgi enzymes involved in the construction of complex oligosaccharides

The distribution of beta 1,2 N-acetylglucosaminyltransferase I (NAGT I), alpha 1,3-1,6 mannosidase II (Mann II), beta 1,4 galactosyltransferase (GalT), alpha 2,6 sialyltransferase (SialylT) was determined by immuno-labelling of cryo-sections from HeLa cell lines. Antibody labelling in the HeLa cell line was made possible by stable expression of epitope-tagged forms of these proteins or forms from species to which specific antibodies were available. NAGT I and Mann II had the same distribution occupying the medial and trans cisternae of the stack. GalT and SialylT also had the same distribution but they occupied the trans cisterna and the trans-Golgi network (TGN). These results generalise our earlier observations on the overlapping distribution of Golgi enzymes and show that each of the trans compartments of the Golgi apparatus in HeLa cells contains unique mixtures of those Golgi enzymes involved in the construction of complex, N-linked oligosaccharides.

Effects of caffeine on cytoplasmic free Ca2+ concentration in pancreatic beta-cells are mediated by interaction with ATP-sensitive K+ channels and L-type voltage-gated Ca2+ channels but not the ryanodine receptor

In the pancreatic beta-cell, an increase in the cytoplasmic free Ca2+ concentration ([Ca2+]i) by caffeine is believed to indicate mobilization of Ca2+ from intracellular stores, through activation of a ryanodine receptor-like channel. It is not known whether other mechanisms, as well, underlie caffeine-induced changes in [Ca2+]i. We studied the effects of caffeine on [Ca2+]i by using dual-wavelength excitation microfluorimetry in fura-2-loaded beta-cells. In the presence of a non-stimulatory concentration of glucose, caffeine (10-50 mM) consistently increased [Ca2+]i. The effect was completely blocked by omission of extracellular Ca2+ and by blockers of the L-type voltage-gated Ca2+ channel, such as D-600 or nifedipine. Depletion of agonist-sensitive intracellular Ca2+ pools by thapsigargin did not inhibit the stimulatory effect of caffeine on [Ca2+]i. Moreover, this effect of caffeine was not due to an increase in cyclic AMP, since forskolin and 3-isobutyl-1-methylxanthine (IBMX) failed to raise [Ca2+]i in unstimulated beta-cells. In beta-cells, glucose and sulphonylureas increase [Ca2+]i by causing closure of ATP-sensitive K+ channels (KATP channels). Caffeine also caused inhibition of KATP channel activity, as measured in excised inside-out patches. Accordingly, caffeine (> 10 mM) induced insulin release from beta-cells in the presence of a non-stimulatory concentration of glucose (3 mM). Hence, membrane depolarization and opening of voltage-gated L-type Ca2+ channels were the underlying mechanisms whereby the xanthine drug increased [Ca2+]i and induced insulin release. Paradoxically, in glucose-stimulated beta-cells, caffeine (> 10 mM) lowered [Ca2+]i. This effect was due to the fact that caffeine reduced depolarization-induced whole-cell Ca2+ current through the L-type voltage-gated Ca2+ channel in a dose-dependent manner. Lower concentrations of caffeine (2.5-5.0 mM), when added after glucose-stimulated increase in [Ca2+]i, induced fast oscillations in [Ca2+]i. The latter effect was likely to be attributable to the cyclic AMP-elevating action of caffeine, leading to phosphorylation of voltage-gated Ca2+ channels. Hence, in beta-cells, caffeine-induced changes in [Ca2+]i are not due to any interaction with intracellular Ca2+ pools. In these cells, a direct interference with KATP channel- and L-type voltage-gated Ca(2+)-channel activity is the underlying mechanism by which caffeine increases or decreases [Ca2+]i.

Inositol 1,2,3-trisphosphate and inositol 1,2- and/or 2,3-bisphosphate are normal constituents of mammalian cells

1. An inositol trisphosphate (InsP3) distinct from Ins(1,4,5)P3 and Ins(1,3,4)P3, which we previously observed in myeloid and lymphoid cells [French, Bunce, Stephens, Lord, McConnell, Brown, Creba and Michell (1991) Proc R. Soc. London B 245, 193-201; Bunce, French, Allen, Mountford, Moore, Greaves, Michell and Brown (1993) Biochem. J. 289, 667-673], is present in WRK1 rat mammary tumour cells and pancreatic endocrine beta-cells. 2. It has been identified as Ins(1,2,3)P3 by a combination of oxidation to ribitol, a structurally diagnostic polyol, and ammoniacal hydrolysis to identified inositol monophosphates. 3. Ins(1,2,3)P3 concentration in HL60 cells changed little during stimulation by ATP or fMetLeuPhe or during neutrophilic or monocytic differentiation, and Ins(1,2,3)P3 was unresponsive to vasopressin in WRK1 cells. 4. Ins(1,2,3)P3 was usually more abundant than Ins(1,4,5)P3, often being present at concentrations between approximately 1 microM and approximately 10 microM. 5. HL60, WRK-1 and lymphoid cells also contain Ins(1,2)P2 or Ins(2,3)P2, or a mixture of these two enantiomers, as a major InsP2 species. 6. Ins(1,2,3)P3 and Ins(1,2)P2/Ins(2,3)P2 are readily detected in cells labelled for long periods, but not in acutely labelled cells. This behaviour resembles that of InsP6, the most abundant cellular inositol polyphosphate that includes the 1,2,3-trisphosphate motif, which also achieves isotopic equilibrium with inositol only slowly. 7. Ins(1,2,3)P3 is the major InsP3 that accumulates during metabolism of InsP6 by WRK-1 cell homogenates. 8. Possible metabolic relationships between Ins(1,2,3)P3, Ins(1,2)P2/Ins(2,3)P2 and other inositol polyphosphates in cells, and a possible role for Ins(1,2,3)P3 in cellular iron handling, are considered.

Assessment of heat pain perception in relation to vibration exposure

The effect of vibration on thin unmyelinated sensory fibers was studied by perception threshold measurement of heat pain. The investigation was a cross-sectional study of 98 vibration-exposed and 53 non-vibration-exposed workers. Pain perception was determined by using the "Marstock" method. The perception threshold of contact heat induced pain was assessed by the method of limits. Quantified personal energy-equivalent vibration exposure was assessed for all subjects on a group basis. The cumulated lifetime equivalent frequency-weighted vibration exposure was estimated based on measurements according to ISO 5349. The mean heat perception threshold was 46.2 degrees C (SD 2.6 degrees C) for the right hand and 46.0 degrees C (SD 2.7 degrees C) for the left. The results showed no mean difference (left = 0.1 degree C, right = 0.6 degree C) in heat pain perception between vibration-exposed and non-exposed subjects. There was a high correlation between the right and left hand measurements (r = 0.81). The risk (rate ratio) for impairment was 1.02 (95% CI 0.81-1.30) for the right hand and 1.00 (95% CI 0.79-1.26) for the left. The results of the study did not indicate any impairment as assessed by an increased perception threshold for heat pain. The lack of an increased heat pain threshold among the vibration-exposed workers in our study cannot exclude a possible lesional somatosensory influence from the exposure, as the lesional effect may also be a lowering of the threshold. The multiple and unrelated percepts of thermal sensations imply that it is not legitimate to draw conclusions about the total status of the small calibre afferents when testing only the heat pain perception.

Vibrotactile perception sensitivity and its relation to hand-arm vibration exposure

Vibrotactile perception thresholds (VPT) at seven test frequencies (8-500 Hz) have been measured and evaluated among 170 male employees at a heavy engineering production workshop, 125 of them were at present, or in the past, exposed to hand-arm vibration. All participants were examined by a physician and none had symptoms of diseases or were exposed to other factors known to cause sensory neuropathies. VPTs [for the three lowest (8-32 Hz; non-Pacinian), for the four highest (63-500 Hz; Pacinian) and for all test frequencies together] and a sensitivity index (SI) has been individually graded in four (normal, slightly deteriorated, deteriorated and seriously deteriorated) and two (normal, abnormal) stages, respectively, and put in relation to individual exposure of vibration. The results do not show any clear relationship on an individual basis between vibration exposure and degraded vibrotactile perception. On a group basis, however, there is a clear tendency towards detoriorated VPTs when the study group is divided in exposure categories. The detorioration is most pronounced in the frequency range mediated by Pacinian corpuscles. In this range an approximately four-fold increase of relative risk for elevated VPT for those in the highest exposure category was observed compared to the non-exposed group. Corresponding relative risk estimate for SI is about 6. Therefore, the results suggest an existence of an exposure-response relationship.

Localization of the Lys, Asp, Glu, Leu tetrapeptide receptor to the Golgi complex and the intermediate compartment in mammalian cells

The carboxyl-terminal Lys-Asp-Glu-Leu (KDEL), or a closely-related sequence, is important for ER localization of both lumenal as well as type II membrane proteins. This sequence functions as a retrieval signal at post-ER compartment(s), but the exact compartment(s) where the retrieval occurs remains unresolved. With an affinity-purified antibody against the carboxyl-terminal sequence of the mammalian KDEL receptor, we have investigated its subcellular localization using immunogold labeling on thawed cryosections of different tissues, such as mouse spermatids and rat pancreas, as well as HeLa, Vero, NRK, and mouse L cells. We show that rab1 is an excellent marker of the intermediate compartment, and we use this marker, as well as budding profiles of the mouse hepatitis virus (MHV) in cells infected with this virus, to identify this compartment. Our results demonstrate that the KDEL receptor is concentrated in the intermediate compartment, as well as in the Golgi stack. Lower but significant labeling was detected in the rough ER. In general, only small amounts of the receptor were detected on the trans side of the Golgi stack, including the trans-Golgi network (TGN) of normal cells and tissues. However, some stress conditions, such as infection with vaccinia virus or vesicular stomatitis virus, as well as 20 degrees C or 43 degrees C treatment, resulted in a significant shift of the distribution towards the trans-TGN side of the Golgi stack. This shift could be quantified in HeLa cells stably expressing a TGN marker. No significant labeling was detected in structures distal to the TGN under all conditions tested. After GTP gamma S treatment of permeabilized cells, the receptor was detected in the beta-COP-containing buds/vesicles that accumulate after this treatment, suggesting that these vesicles may transport the receptor between compartments. We propose that retrieval of KDEL-containing proteins occurs at multiple post-ER compartments up to the TGN along the exocytotic pathway, and that within this pathway, the amounts of the receptor in different compartments varies according to physiological conditions.

Oscillations in cytoplasmic free calcium concentration in human pancreatic islets from subjects with normal and impaired glucose tolerance

Plasma insulin levels in healthy subjects oscillate and non-insulin-dependent diabetic patients display an irregular pattern of such oscillations. Since an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) in the pancreatic beta cell is the major stimulus for insulin release, this study was undertaken to investigate the dynamics of electrical activity, [Ca2+]i-changes and insulin release, in stimulated islets from subjects of varying glucose tolerance. In four patients it was possible to investigate more than one of these three parameters. Stimulation of pancreatic islets with glucose and tolbutamide sometimes resulted in the appearance of oscillations in [Ca2+]i, lasting 2-3 min. Such oscillations were observed even in some islets from patients with impaired glucose tolerance. In one islet from a diabetic patient there was no response to glucose, whereas that islet displayed [Ca2+]i-oscillations in response to tolbutamide, suggesting that sulphonylurea treatment can mimic the complex pattern of glucose-induced [Ca2+]i-oscillations. We also, for the first time, made patch-clamp recordings of membrane currents in beta-cells in situ in the islet. Stimulation with glucose and tolbutamide resulted in depolarization and appearance of action potentials. The islet preparations responded to stimulation with a number of different secretagogues with release of insulin. The present study shows that human islets can respond to stimulation with glucose and sulphonylurea with oscillations in [Ca2+]i, which is the signal probably underlying the oscillations in plasma insulin levels observed in healthy subjects. Interestingly, even subjects with impaired glucose tolerance had islets that responded with oscillations in [Ca2+]i upon glucose stimulation, although it is not known to what extent the response of these islets was representative of most islets in these patients.

Retention and retrieval in the endoplasmic reticulum and the Golgi apparatus

Resident proteins of the exocytic pathway contain at least two types of information in their primary sequence for determining their subcellular location. The first type of information is found at the carboxyl terminus of soluble proteins of the endoplasmic reticulum (ER) and in the cytoplasmic domain of some ER and Golgi membrane proteins. It acts as a retrieval signal, returning proteins that have left the compartment in which they reside. The second type of information has been found in the membrane-spanning domain of several ER and Golgi proteins and, though the mechanism by which it operates is still unclear, it acts as a retention signal, keeping the protein at a particular location within the organelle. The presence of both a retrieval signal and a retention signal in a trans-Golgi network resident protein suggests that more than one mechanism operates to ensure correct localization of resident proteins along the exocytic pathway.

Impaired nerve conduction in the carpal tunnel of platers and truck assemblers exposed to hand-arm vibration

OBJECTIVES

The goal of this study was to assess the relative risks of sustaining impaired nerve conduction in the hands among vibration-exposed persons as opposed to nonvibration-exposed referents.

METHODS

In a cross-sectional study design platers and truck assembly workers were contrasted to office workers. The 4-h frequency-weighted vibration was 4.6 m.s-2 and 1.0 m.s-2 for the platers and assemblers, respectively. The ergonomic factors were measured as forced grip time. The conduction velocity, distal latency time, and amplitude of the median nerve were measured for both hands.

RESULTS

The sensory nerve conduction velocity was slower in the right hand than in the left. An increased risk of prolonged latency time was found for the platers and assemblers when contrasted to the office workers. The relative risks (rate ratios) of impaired nerve conduction for the carpal tunnel segment varied between 1.4 and 2.0 for the distal latency and between 0.9 and 1.7 for the nerve conduction velocity. The rate ratios were generally higher for the left-hand side than for the right-hand side. The risks were not proportional to either the weighted or unweighted vibration exposure.

CONCLUSIONS

The contributions from vibration and ergonomic factors to impaired nerve conduction velocity were inseparable in this study. Ergonomic factors such as forceful gripping and extreme positions, apart from vibration exposure, may be strong determinants of impaired nerve conduction in the carpal tunnel area.

Toxic PCB congeners and organochlorine pesticides in Italian human milk

Human milk from four major Italian cities was analyzed for individual congeners of polychlorinated biphenyls (PCB), DDT, DDE, hexachlorobenzene, and beta-hexachlorocyclohexane. Minimum and maximum concentrations in milk from individual mothers for most compounds ranged between one order of magnitude below and above the mean value of all mothers. Good agreements were found between results from pooled samples and mean values of individual samples. No statistically significant difference between cities was found and the levels in milk from Italian mothers did not differ significantly from published levels from other parts of the world. Principal component analyses revealed that the PCB congener distribution pattern was very similar in all mothers, independent of location. Average concentrations in milk from the four cities were 19(+/- 5) micrograms liter-1 total PCB or 3.2(+/- 0.8) ng liter-1 toxicity equivalents according to the most conservative TCDD toxicity equivalent factors of PCBs proposed in the literature, 70(+/- 18) micrograms liter-1 DDE, 4.5(+/- 1.2) micrograms liter-1 DDT, 5.6(+/- 1.9) micrograms liter-1 HCB, and 4.4(+/- 1.7) micrograms liter-1 beta-hexachlorocyclohexane.

The TGN38 glycoprotein contains two non-overlapping signals that mediate localization to the trans-Golgi network

The membrane-spanning and cytoplasmic domains of CD4 and CD8 were replaced by those of TGN38. After transient expression in HeLa cells, the location of the hybrid proteins was determined using immunofluorescence and quantitative immuno-electron microscopy, FACS analysis and metabolic labeling. The membrane-spanning domain was found to contain a signal that localized hybrid proteins to the TGN. This was in addition to the signal previously identified in the cytoplasmic domain (Bos, K., C. Wraight, and K. Stanley. 1993. EMBO (Eur. Mol. Biol. Organ) J. 12:2219-2228. Humphrey, J. S., P. J. Peters, L. C. Yuan, and J. S. Bonifacino. 1993. J. Cell Biol. 120:1123-1135. Wong, S. H., and W. Hong. 1993. J. Biol. Chem. 268:22853-22862). The different properties of these two signals suggest that each operates by a different mechanism.

Isolation of a matrix that binds medial Golgi enzymes

Rat liver Golgi stacks were extracted with Triton X-100 at neutral pH. After centrifugation the low speed pellet contained two medial-Golgi enzymes, N-acetylglucosaminyltransferase I and mannosidase II, but no enzymes or markers from other parts of the Golgi apparatus. Both were present in the same structures which appeared, by electron microscopy, to be small remnants of cisternal membranes. The enzymes could be removed by treatment with low salt, leaving behind a salt pellet, which we term the matrix. Removal of salt caused specific re-binding of both enzymes to the matrix, with an apparent dissociation constant of 3 nM for mannosidase II. Re-binding was abolished by pretreatment of intact Golgi stacks with proteinase K, suggesting that the matrix was present between the cisternae.

Kin recognition between medial Golgi enzymes in HeLa cells

The medial Golgi enzymes, N-acetylglucosaminyltransferase I (NAGT I) and mannosidase II (Mann II), and the trans Golgi enzyme, beta-1,4-galactosyltransferase (GalT) were each retained in the endoplasmic reticulum (ER) by grafting on the cytoplasmic tail of the p33 invariant chain. Transient and stable expression of p33/NAGT I in HeLa cells caused relocation of endogenous Mann II to the ER and transient expression of p33/Mann II had a similar effect on endogenous NAGT I. Neither of these endogenous medial enzymes were affected by transient expression of p33/GalT. These data provide strong evidence for kin recognition between medial Golgi enzymes and suggest a role for them in the organization of the Golgi stack.

Simultaneous oscillations of cytoplasmic free Ca2+ concentration and Ins(1,4,5)P3 concentration in mouse pancreatic beta-cells

Changes in the cytoplasmic free Ca2+ concentration ([Ca2+]i) in stimulated cells are often oscillatory, but the mechanisms that drive these oscillations are still a matter of controversy: different models of the generation of these [Ca2+]i oscillations make different assumptions as to whether oscillations in Ins(1,4,5)P3 concentration are necessary for this process. We have looked for changes in inositol polyphosphate levels that might occur in suspensions of murine pancreatic beta-cells when these cells are induced to display synchronized oscillations in [Ca2+]i by the sequential addition of glucose, an alpha 2-adrenergic stimulus and extracellular Ca2+. The intracellular level of Ins(1,4,5)P3 oscillated in a manner approximately in synchrony with changes in [Ca2+]i. Oscillations in the levels of Ins(1,4,5)P3 metabolites [Ins(1,3,4)P3 and inositol bisphosphates] were slightly delayed relative to the Ins(1,4,5)P3 oscillations, and the concentration of Ins(1,3,4,5,6)P5 remained approximately constant during the [Ca2+]i oscillations. These results demonstrate that [Ins(1,4,5)P3] and [Ca2+]i oscillate in synchrony in at least one type of cell. Whether such oscillations in intracellular [Ins(1,4,5)P3] provide a primary driving force for [Ca2+]i oscillations either in beta-cells or in other stimulated cells remains to be determined. Even if they do not, the [Ins(1,4,5)P3] oscillations will at least provide an amplifying influence on the [Ca2+]i changes.

Enhanced stimulus-secretion coupling in polyamine-depleted rat insulinoma cells. An effect involving increased cytoplasmic Ca2+, inositol phosphate generation, and phorbol ester sensitivity

To extend previous observations on the role of polyamines in insulin production, metabolism, and replication of insulin-secreting pancreatic beta cells, we have studied the role of polyamines in the regulation of the stimulus-secretion coupling of clonal rat insulinoma cells (RINm5F). For this purpose, RINm5F cells were partially depleted in their polyamine contents by use of the specific ornithine decarboxylase inhibitor difluoromethylornithine (DFMO), which led to an increase in cellular insulin and ATP contents. Analysis of different parts of the signal transduction pathway revealed that insulin secretion and the increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) after K(+)-induced depolarization were markedly enhanced in DFMO-treated cells. These effects were paralleled by increased voltage-activated Ca2+ currents, as judged by whole-cell patch-clamp analysis, probably reflecting increased channel activity rather than elevated number of channels per cell. DFMO treatment also rendered phospholipase C in these cells more sensitive to the muscarinic receptor agonist carbamylcholine, as evidenced by enhanced generation of inositol phosphates, increase in [Ca2+]i and insulin secretion, despite an unaltered ligand binding to muscarinic receptors and lack of effect on protein kinase C activity. In addition, the tumor promoter 12-O-tetradecanoylphorbol 13-acetate, at concentrations suggested to be specific for protein kinase C activation, evoked an increased insulin output in polyamine-deprived cells compared to control cells. The stimulatory effects of glucose or the cyclic AMP raising agent theophylline on insulin release were not increased by DFMO treatment. In spite of increased binding of sulfonylurea in DFMO-treated cells, there was no secretory response or altered increase in [Ca2+]i in response to the drug in these cells. It is concluded that partial polyamine depletion sensitizes the stimulus-secretion coupling at multiple levels in the insulinoma cells, including increased voltage-dependent Ca2+ influx and enhanced responsiveness to activators of phospholipase C and protein kinase C. In their entirety, our present results indicate that the behavior of the stimulus-secretion coupling of polyamine-depleted RINm5F insulinoma cells changes towards that of native beta cells, thus improving the usefulness of this cell line for studies of beta cell insulin secretion.

Kin recognition. A model for the retention of Golgi enzymes

The surprising result that the spanning domain causes retention of proteins in the Golgi stack poses the question as to the actual mechanism. Here we present a simple model that might have general applicability.

Cytochrome bo from E. coli does not exhibit the same proton transfer characteristics as the bovine cytochrome c oxidase during oxygen reduction

The reaction where fully reduced cytochrome bo from E. coli partially reduces dioxygen has been characterized with respect to the kinetics of the associated proton uptake, and with respect to the pH- and D2O-sensitivity of the electron transfer reactions. A monophasic proton uptake with a rate constant of about 8 x 10(3) s-1 and a stoichiometry of 0.8 H+/bo were recorded, using the indicator dye, Cresol red, at pH 8.2. The electron transfer reactions were independent of pH in the range 6.0-9.5 and were not affected by exchanging H2O to D2O as solvent. Comparison of these results with those obtained in an earlier investigation of the bovine cytochrome c oxidase [(1992) Biochemistry 31, 11853-11859], indicates differences between the two oxidases with respect to the role of protons in oxygen reduction and/or the mechanism of proton uptake from the medium.