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Biomedical subjects

O Larsson

Publications and source records attributed to O Larsson.

At least 145 records · Page 8Linked to original sources
PubMed1991

Inositol trisphosphate-dependent periodic activation of a Ca(2+)-activated K+ conductance in glucose-stimulated pancreatic beta-cells.

Glucose-stimulated insulin secretion is associated with the appearance of electrical activity in the pancreatic beta-cell. At intermediate glucose concentrations, beta-cell electrical activity follows a characteristic pattern of slow oscillations in membrane potential on which bursts of action potentials are superimposed. The electrophysiological background of the bursting pattern remains unestablished. Activation of Ca(2+)-activated large-conductance K+ channels (KCa channel) has been implicated in this process but seems unlikely in view of recent evidence demonstrating that the beta-cell electrical activity is unaffected by the specific KCa channel blocker charybdotoxin. Another hypothesis postulates that the bursting arises as a consequence of two components of Ca(2+)-current inactivation. Here we show that activation of a novel Ca(2+)-dependent K+ current in glucose-stimulated beta-cells produces a transient membrane repolarization. This interrupts action potential firing so that action potentials appear in bursts. Spontaneous activity of this current was seen only rarely but could be induced by addition of compounds functionally related to hormones and neurotransmitters present in the intact pancreatic islet. K+ currents of the same type could be evoked by intracellular application of GTP, the effect of which was mediated by mobilization of Ca2+ from inositol 1,4,5-trisphosphate (InsP3)-sensitive intracellular Ca2+ stores. These observations suggest that oscillatory glucose-stimulated electrical activity, which is correlated with pulsatile release of insulin, results from the interaction between the beta-cell and intraislet hormones and neurotransmitters. Our data also provide evidence for a close interplay between ion channels in the plasma membrane and InsP3-induced mobilization of intracellular Ca2+ in an excitable cell.

Animals↗
PubMed1991

Separate processes mediate nucleotide-induced inhibition and stimulation of the ATP-regulated K(+)-channels in mouse pancreatic beta-cells.

The mechanisms by which nucleotides stimulate the activity of the ATP-regulated K(+)-channel (KATP-channel) were investigated using inside-out patches from mouse pancreatic beta-cells. ATP produces a concentration-dependent inhibition of channel activity with a Ki of 18 microns. The inhibitory action of ATP was counteracted by ADP (0.1 mM) and GDP (0.2 mM) but not GTP (1 mM). Stimulation of channel activity was also observed when ADP, GDP and GTP were applied in the absence of ATP. The ability of ADP and GDP to reactivate KATP-channels blocked by ATP declined with time following patch excision and after 30-60 min these nucleotides were without effect. During the same time period the ability of ADP and GTP to stimulate the channel in the absence of ATP was lost. In fact, ADP now blocked channel activity with 50% inhibition being observed at approximately 0.1 mM. By contrast, GDP remained a stimulator in the absence of ATP even when its ability to evoke channel activity in the presence of ATP was lost. These observations show that nucleotide-induced activation of the KATP-channel does not involve competition with ATP for a common inhibitory site but involves other processes. The data are consistent with the idea that nucleotides modulate KATP-channel activity by a number of different mechanisms that may include both regulation of cytosolic constituents and direct interaction with the channel and associated control proteins.

Adenosine Diphosphate↗
PubMed1991

Activation by adrenaline of a low-conductance G protein-dependent K+ channel in mouse pancreatic B cells.

Insulin is produced and secreted by the B cells in the endocrine pancreas. In vivo, insulin secretion is under the control of a number of metabolic, neural and hormonal substances. It is now clear that stimulation of insulin release by fuel secretagogues, such as glucose, involves the closure of K+ channels that are sensitive to the intracellular ATP concentration (KATP channels). This leads to membrane depolarization and the generation of Ca2(+)-dependent action potentials. The mechanisms whereby hormones and neurotransmitters such as adrenaline, galanin and somatostatin, which are released by intraislet nerve endings and the pancreatic D cells, produce inhibition of insulin secretion are not clear. Here we show that adrenaline suppresses B-cell electrical activity (and thus insulin secretion) by a G protein-dependent mechanism, which culminates in the activation of a sulphonylurea-insensitive low-conductance K+ channel distinct from the KATP channel.

Animals↗
PubMed1991

Characterization, localization and actions of endothelins in umbilical vessels and placenta of man.

Endothelin-like immunoreactivity was observed in the endothelial lining of umbilical vein and artery as well as in the epithelium of the amniotic membrane. High levels of endothelin-like immunoreactivity (0.4-1.4 pmol g-1) were detected in human amniotic membrane, umbilical vessels and placenta. The concentration of endothelin-like immunoreactivity in the amniotic fluid was much higher (77 pmol l-1) than in umbilical cord plasma (10 pmol l-1). Characterization by reverse phase HPLC revealed that most of the endothelin-like immunoreactivity eluted in the position of synthetic endothelin-1 or oxidized endothelin-1. Specific, high affinity binding sites for endothelin-1 were present in placenta and umbilical artery. Endothelin binding sites were also found in cultured smooth muscle cells from the umbilical artery and vein. In the placenta, endothelin-1 and -3 were almost equipotent as competing ligands for endothelin-1 binding sites, whereas in the umbilical artery endothelin-3 was much less potent than endothelin-1. Scatchard analysis of the binding for placental membranes displayed a straight line (r = -0.994) indicating a single class of endothelin receptors with a Kd-value of 80 pmol l-1 and Bmax of 113 fmol mg-1. Endothelin-1 caused potent contractions of umbilical arteries and veins with threshold effects at 10 pmol l-1 while endothelin-3 had no contractile effect up to 10(-7) mol l-1. It is concluded that endothelin-1 predominates over other endothelins in umbilical vessels, amnion and placenta, and high levels of endothelin-1 was observed in foetal circulation and amniotic fluid. Endothelin-receptors seem to be of different types in placenta (ETB type) and umbilical vessels (ETA type).

Amniotic Fluid↗
PubMed1990

Human fibroblasts show expression of the leukotriene-A4-hydrolase gene, which is increased after simian-virus-40 transformation.

Human fibroblasts in cell culture converted the epoxide intermediate leukotriene A4 into the potent chemotaxin leukotriene B4. The identity of leukotriene B4 was ascertained by its mobility in reverse-phase high performance liquid chromatography, ultraviolet spectroscopy and gas chromatography/mass spectrometry. The presence of the enzyme responsible for the conversion (i.e. leukotriene A4 hydrolase), as well as the corresponding mRNA, were demonstrated by Western and Northern blot analyses. Leukotriene-A4-hydrolase enzyme activity, protein and mRNA were all enhanced (approximately threefold) in human fibroblasts that had been transformed by simian virus 40.

Cell Line↗
PubMed1990

Analgesic efficacy of acetaminophen sustained release.

The analgesic efficacy of acetaminophen sustained release (SR) and acetaminophen immediate plus sustained release (IR + SR) was evaluated in 200 outpatients with pain after oral surgery. Under double-blind conditions SR high dose (2000 mg) or low dose (1000 mg), IR + SR high dose (500 + 1500 mg) or low dose (250 + 750 mg), or acetaminophen standard tablet high dose (1000 mg) or low dose (500 mg) were randomly administered after removal of a lower third molar. The hourly pain intensity was rated on a visual analog scale during 12 hours. The efficacy was based on peak effect (maximum pain intensity difference in percent), pain reduction (mean percentage pain intensity difference), duration of effect (time to remedication) and pain reduction index (pain reduction multiplied by duration of effect). Pain reduction was 37% with the 500-mg tablet and 54% with SR 2000 mg. The peak effect increased from 53% after 1.9 hours for the 500-mg tablet to 67% after 2.6 hours for SR 2000 mg. The SR formulation significantly increased the duration of effect without reduction in peak effect.

Acetaminophen↗
PubMed1990

Calcitonin gene-related peptide stimulates proliferation of human endothelial cells.

The effects of the vasoactive perivascular neuropeptides calcitonin gene-related peptide (CGRP), neurokinin A (NKA), neuropeptide Y (NPY), and vasoactive intestinal polypeptide (VIP) on proliferation of cultured human umbilical vein endothelial cells (HUVECs) were investigated. CGRP was shown to increase both cell number and DNA synthesis, whereas NKA, NPY, and VIP were ineffective. 125I-labeled CGRP was shown to bind to HUVECs and this binding was displaced by addition of unlabeled CGRP, suggesting the existence of specific CGRP receptors. The effect of CGRP on formation of adenosine 3',5'-cyclic monophosphate (cAMP) and inositol phosphates (InsP), two intracellular messengers known to be involved in regulation of cell proliferation, was investigated. CGRP stimulated cAMP formation but was without effect on the formation of InsP. Proliferation, as well as cAMP formation, was also stimulated by cholera toxin. Basic fibroblast growth factor stimulated growth without affecting cAMP or InsP formation, whereas thrombin, which increased InsP formation, did not stimulate proliferation. We thus suggest that CGRP may act as a local factor stimulating proliferation of endothelial cells; that the mechanism of action is associated with cAMP formation; and that this effect of CGRP may be important for formation of new vessels during physiological and pathophysiological events such as ischemia, inflammation, and wound healing.

Calcitonin↗
PubMed1990

VIP and forskolin enhance carbachol-induced K+ efflux from rat salivary gland fragments by a Ca2(+)-sensitive mechanism.

The effect of vasoactive intestinal peptide (VIP) and forskolin on carbachol-induced K+ release from superfused rat submandibular and parotid gland fragments was examined using a K(+)-sensitive electrode. Carbachol (0.1, 1, and 10 microM) superfused over the glandular fragments for 15 min caused a concentration-dependent, transient elevation of K+ efflux, with a peak value after approximately 5 min. The carbachol-induced release of K+ could be divided into two distinct components, one transient peak lasting 5-8 min independent of extracellular Ca2+ and a second component of K+ release dependent on Ca2+ in the perfusion medium. VIP (1 microM) lacked effect on K+ efflux on its own but increased the carbachol (1 microM)-evoked K+ release. The VIP effects on K+ efflux were mimicked by forskolin (10 microM). Omission of Ca2+ from the medium totally abolished the augmenting effect of VIP and forskolin on carbachol-evoked K+ efflux. The Ca2+ ionophore A23187 (1 or 10 microM) induced a prolonged low-rate efflux of K+, which was dependent on Ca2+ in the medium. This effect of A23187 on K+ secretion was potentiated by forskolin (10 microM). The Na(+)-K(+)-ATPase blocker ouabain did not affect K+ release on its own, a lack of effect which remained following pretreatment with forskolin. It is concluded that VIP, by increasing the intracellular levels of cAMP in the glandular cell, potentiates carbachol-evoked Ca2(+)-dependent K+ efflux. These results may help to explain the synergistic effects of the coexisting transmitters VIP and acetylcholine.

Animals↗
PubMed1989

Abolition of mevinolin-induced growth inhibition in human fibroblasts following transformation by simian virus 40.

The basal level of the gene expression and the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase was higher in SV40-transformed human fibroblasts (90-VA VI) than in normal ones (HDF). In both these cell types mevinolin (25 microM) caused an 85-90% depression of HMG CoA reductase activity and of the incorporation of [3H]acetate into sterols. In HDF this was coupled to an efficient block of cell growth, whereas the growth of 90-VA VI was only slightly reduced by mevinolin. In HDF, mevinolin (25 microM) also abolished essentially all dilichol synthesis, as measured by incorporation of [3H]acetate. In contrast, dolichol synthesis remained unaltered, or was increased, in mevinolin-treated 90-VA VI. We suggest that these different responses of dolichol synthesis may depend on different substrate affinities of the rate-limiting enzyme in the dolichol pathway. However, if 90-VA VI was treated with 25-hydroxycholesterol (25-OH), an alternative inhibitor of HMG CoA reductase, the cellular growth as well as dolichol synthesis was significantly decreased. Since the inhibitory effect of 25OH on HMG CoA reductase activity did not exceed that of mevinolin, it seems that 25-OH, besides HMG CoA reductase, inhibits steps distal to HMG CoA reductase. This notion was further supported by the finding that addition of mevalonate did not prevent the 25-OH-induced growth inhibition. However, if dolichol was added along with 25-OH, the block was partially prevented, indicating that a critical level of de novo synthesis of dolichol for cellular growth.

Cell Division↗
PubMed1989

Bradykinin blocks the action of EGF, but not PDGF, on fibroblast division.

Quiescent fibroblasts derived from human fetal lung can be stimulated to reinitiate DNA synthesis by sequential addition of 3 nM IGF-1 and a low concentration (8 pM) of EGF or by continuous exposure to 10% fetal calf serum or 10 ng/ml PDGF. Bradykinin blocks the IGF-1 and EGF-dependent signals without affecting the response to serum or PDGF. It activates protein kinase C and its anti-mitogenic effect is abolished after this kinase has been down-regulated. Bradykinin has no effect on the binding affinity of the EGF receptor whereas phorbol ester induces its 'transmodulation' to low affinity.

Blood↗
PubMed1989

The role of N-linked glycosylation in the regulation of activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and proliferation of SV40-transformed 3T3 cells.

The effects of glycosylation inhibitors on the proliferation of SV40-transformed 3T3 cells (SV-3T3) were examined in vitro. Whereas swainsonine and castanospermine, which inhibit distal steps in the glycosylational processing, exerted marginal or no effects on cell proliferation, a proximal inhibitor, tunicamycin, efficiently decreased the rate of DNA synthesis and also inhibited the activity of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. The inhibitory effects of tunicamycin on cell proliferation could be partially reversed by addition of dolichol, a metabolite in the pathway regulated by HMG-CoA reductase. This finding suggests that tunicamycin exerts at least one of its effects on cell proliferation by modulating the activity of HMG-CoA reductase.

Animals↗
PubMed1989

Cell cycle regulation of human diploid fibroblasts: possible mechanisms of platelet-derived growth factor.

Cell-cycle regulation of human diploid fibroblasts (HDF) is located in the proximal half of G1, designated G1-pm (G1-postmitosis). In order to traverse this subphase, cells require serum factors or PDGF. However, when cells have traversed into the distal half of G1, designated G1-ps (G1-pre-DNA synthesis), they become independent of serum or PDGF and progress through the remainder of the cell cycle at an invariable rate. From this, it follows that a specific G1-pm block can be induced by serum depletion. A similar G1-pm block could also be induced by a moderate inhibition of overall protein synthesis following treatment with CHM. Even this block could be prevented by the addition of PDGF, suggesting that a high level of protein synthesis in itself is not necessary for sustaining cell-cycle traverse. Nevertheless, a critical accumulation of some specific proteins might be required for the G1-pm/G1-ps-transition. However, the underlying mechanisms of modulation of the accumulation of such proteins by PDGF must involve alternative regulatory events (e.g., gene expression, protein stabilization) rather than protein synthesis. Among the possible cell cycle-regulatory proteins, the present study focused on 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase. This enzyme is regulated by various kinds of control mechanisms and regulates the biosynthesis of sterols and nonsterol isoprenes, some of which are proposed to be necessary for mammalian cell growth (Brown and Goldstein, 1980). The present results suggest that regulation of HMG CoA reductase may be involved in the control of the G1-pm/G1-ps-progression in HDF.

Blotting, Northern↗
PubMed1989

Carbachol stimulation of inositol phosphate accumulation in rat submandibular gland fragments is not modified by VIP.

Formation of inositol phosphates in response to carbachol, phenylephrine and vasoactive intestinal polypeptide (VIP) was studied after labelling with [3H]myo-inositol in rat submandibular gland fragments. Carbachol enhanced the accumulation of inositol phosphates in a concentration-dependent manner. This effect was independent of calcium in the incubation medium and totally antagonized by atropine (IC50 = approx. I nM). Phenylephrine also induced an increase in inositol phosphate accumulation, which was totally antagonized by prazosin but not by atropine. Vasoactive intestinal polypeptide, isoproterenol and forskolin, compounds known to enhance the levels of cAMP in rat salivary gland, or addition of dibutyryl-cAMP (DB-cAMP) failed to alter basal or carbachol-evoked accumulation of inositol phosphates. It is concluded that the formation of inositol phosphates during muscarinic receptor stimulation with carbachol in rat submandibular gland fragments is not affected by adrenoceptor occupation or by cAMP. In particular, addition of VIP, which coexists with acetylcholine, did not alter the muscarinic inositol phosphate response.

Animals↗
PubMed1989

The enhancement of carbachol-induced salivary secretion by VIP and CGRP in rat parotid gland is mimicked by forskolin.

Low doses of vasoactive intestinal polypeptide (VIP) and calcitonin gene-related peptide (CGRP) have been shown to augment the salivary volume secretion evoked by muscarinic receptor agonists or substance P (SP) in rat parotid gland. Since VIP and CGRP are known to activate adenylate cyclase, we have studied whether forskolin, which directly activates this enzyme, can mimic the effects of these peptides on salivary secretion from the parotid gland in anaesthetized (Inactin 0.5 g kg-1 i.p.) rats. We have also studied the effect of the secretagogues and peptides on glandular blood flow as revealed by the laser Doppler technique. Carbachol (5 nmol kg-1) and SP (185 pmol kg-1) injected i.v. caused a transient increase in parotid blood flow and a decrease in systematic blood pressure concomitant with a salivary secretion of 3.3 +/- 0.3 mg (n = 22) and 18.7 +/- 1.9 mg (n = 25) respectively. VIP (150 pmol kg-1) and CGRP (25 pmol kg-1) also caused a transient increase in glandular blood flow concomitant with a decrease in systemic blood pressure, but no salivary secretion. The glandular blood flow increased by 166 +/- 5% and 43 +/- 11% for VIP and CGRP respectively. When carbachol was given 20 s after the injection of VIP or CGRP, the secretory response was increased by about 250% and 60% respectively. The adenylate cyclase stimulator forskolin (2.5 pmol kg-1) produced the same type of response regarding blood flow and systemic blood pressure as VIP and CGRP and potentiated the salivary secretion evoked by carbachol (5 nmol kg-1) by about 100%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗