Biomedical subjects

K Sumikawa

Publications and source records attributed to K Sumikawa.

At least 73 records · Page 4Linked to original sources

PubMed1997

Short-term depression and long-term enhancement of ACh-gated channel currents induced by linoleic and linolenic acid.

The effects of cis-unsaturated free fatty acids such as linoleic and linolenic acid on ACh-evoked currents were examined using normal and mutant nicotinic acetylcholine (ACh) receptors lacking protein kinase C (PKC) phosphorylation sites on the alpha and delta subunits expressed in Xenopus oocytes. These free fatty acids reduced ACh-gated channel currents during treatment and to a greater extent in Ca2+-free extracellular solution. After treatment, the currents were enhanced as the drug was washed out, but this effect was not observed in the absence of extracellular Ca2+. Linolenic acid was more potent of the current enhancement (300% of the control) than linoleic acid (190% of the control). The current enhancement induced by these free fatty acids was inhibited by the selective PKC inhibitor, GF109203X, while the current depression was not affected. Furthermore, these lipids decreased ACh-evoked currents in mutant ACh receptors to the same extent as in normal ACh receptors, but never enhanced the currents. These results indicate that linoleic and linolenic acid have biphasic actions on ACh receptor currents; a short-term depression and a long-term enhancement. The short-term depression may be due to an interaction with the ACh receptor channels, presumably at Ca2+ binding sites. The long-lasting enhancement appears to result from Ca2+-dependent PKC activation followed by PKC phosphorylation of the ACh receptors.

Acetylcholine↗

PubMed1997

Oleic acid enhances ACh receptor currents by activation of Ca2+/calmodulin-dependent protein kinase II.

Oleic acid, a cis-unsaturated free fatty acid, is proposed to be involved in the protein kinase C (PKC) activation pathway. Its biological actions, however, have not been well-characterized. We examined the effects of oleic acid on acetylcholine (ACh)-gated channel currents using Torpedo nicotinic ACh receptors expressed in Xenopus oocytes. Oleic acid (10 microM) enhanced the currents, reaching a maximum (140%) 20 min after treatment, while no enhancement was observed in Ca(2+)-free extracellular solution. The current potentiation by oleic acid was not inhibited by PKC inhibitors such as PKCI or GF109203X. Furthermore, oleic acid potentiated the currents in mutant ACh receptors lacking potential PKC phosphorylation sites. In contrast, the potentiation was fully inhibited by a CaMKII inhibitor, KN-62. These results strongly suggest that oleic acid potentiates ACh receptor currents by activation of calmodulin-dependent protein kinase II (CaMKII), independent of the PKC pathway.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1997

Adenovirus-mediated NMDA receptor knockouts in the rat hippocampal CA1 region.

Adenoviral antisense constructs of the rat N-methyl-D-aspartate (NMDA) receptor subunit 1 (R1) were assessed for creating NMDAR1 knockouts in rat hippocampal CA1 regions in vivo. In situ hybridization analyses showed that virus-derived antisense transcripts were detected up to 5 weeks postinfection (p.i.). Although immunological methods failed to demonstrate a reduction of NMDA receptor protein, whole-cell recording showed that neurons in the transduced regions were deficient in NMDA receptor-mediated synaptic currents, but not alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor (AMPAR)-mediated synaptic currents. Thus, the data suggest that adenovirus technology can be used to locally knockout specific gene function for dissecting molecular mechanisms of synaptic plasticity.

2-Amino-5-phosphonovalerate↗

PubMed1997

N-glycosylation at the conserved sites ensures the expression of properly folded functional ACh receptors.

The role of the conserved carbohydrate moiety in the expression of complete acetylcholine receptor (AChR), alpha2 beta gamma delta was re-investigated by expressing additional site-directed mutant subunits, lacking an N-glycosylation site, in Xenopus oocytes. All mutant subunits were stably expressed and appeared to associate with other normal subunits; however, removal of carbohydrate on the alpha subunit inhibited the formation of 125I-alpha-bungarotoxin (alpha-BuTX) binding sites and functional ACh-gated ion channels. 125I-alpha-BuTX binding to AChRs was also significantly reduced by removal of the conserved carbohydrate on the gamma or delta subunits. Immunoprecipitation with monoclonal antibodies that recognize the two distinct alpha-BuTX sites on the AChR indicated that the mutant gamma subunit did not interfere with efficient formation of the alpha-BuTX binding site at the alpha/delta interface, but loss of the carbohydrate did interfere with formation of the alpha-BuTX binding site at the alpha/mutant gamma interface. A similar result was obtained with the mutant delta subunit. Furthermore, the mutant gamma and mutant delta subunits were not incorporated efficiently into the mature (correct tertiary conformation capable of alpha-BuTX binding) alpha beta delta or alpha beta gamma complexes, respectively. Since both mutant gamma and mutant delta subunits were capable of assembling with the alpha subunits (immature assembly), these results suggest that the formation of the two alpha-BuTX binding sites requires correct folding of the alpha gamma and alpha delta complexes, which is aided by the conserved carbohydrate on the gamma and delta subunits. Electrophysiological experiments demonstrated that functional receptors containing mutant subunits were produced, but the functional properties of the mutant receptors were differentially altered, depending on the subunit mutated. Together, our results suggest that N-glycosylation of AChR subunits ensures the correct folding of important functional domains and expression of proper functional receptors in the plasma membrane.

Acetylcholine↗

PubMed1997

Long-lasting enhancement of ACh receptor currents by lysophospholipids.

Lysophosphatidylcholine (LysoPtdCho) and lysophosphatidylethanolamine (LysoPtdEtn), which are formed by phospholipase A2-catalyzed hydrolysis of phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn), respectively, are proposed to be involved in protein kinase C (PKC) activation. Their physiological significance, however, remains unclear. We examined the effects of lysoPtdCho and lysoPtdEtn on acetylcholine (ACh) receptor currents using oocytes expressing Torpedo nicotinic ACh receptors. LysoPtdCho enhanced the currents in a washing time- and dose-dependent manner (10 nM-1 microM), reaching a maximum of 191% at 20 min after treatment. The currents were enhanced to a lesser extent at higher concentrations, and instead, inhibited to 81% at 10 microM. Likewise, lysoPtdEtn also potentiated the currents to 200% at 10 microM, although its dose-dependent curve shifted to right as compared with that of lysoPtdCho. The current potentiation was blocked by a PKC inhibitor, PKC inhibitor peptide (PKCI), or removal of extracellular Ca2+. In addition, lysoPtdCho and lysoPtdEtn enhanced the currents in mutant ACh receptors lacking PKC phosphorylation sites on the alpha and delta subunits. These results suggest that lysophospholipids such as lysoPtdCho and lysoPtdEtn potentiated ACh receptor currents by Ca2+-dependent PKC activation, but that this effect did not require PKC phosphorylation of the ACh receptor.

Acetylcholine↗

PubMed1997

Catecholamine and renin-angiotensin response during controlled hypotension induced by prostaglandin E1 combined with hemodilution during isoflurane anesthesia.

STUDY OBJECTIVE: To evaluate the catecholamine and renin-angiotensin response during controlled hypotension combined with hemodilution in the clinical setting. DESIGN: Randomized, prospective study. SETTING: Inpatient surgery at Nagasaki Rosai Hospital. PATIENTS: 30 ASA physical status I and II female patients scheduled for total hip arthroplasty. INTERVENTIONS: Patients were randomly divided into three groups. Group A (N = 10) received hemodilution alone. Group B (N = 10) received controlled hypotension alone. Group C (N = 10) received hemodilution plus controlled hypotension. Hemodilution was carried out after induction of anesthesia, in which drawn blood was replaced with 6% hydroxyethyl starch, and the final hematocrit value was approximately 22%. Controlled hypotension was induced with prostaglandin E1 (PGE1) to maintain mean arterial blood pressure at 55 mmHg for 80 minutes. MEASUREMENTS AND MAIN RESULTS: Measurements included plasma renin activity (RA) and plasma concentrations of angiotensin-II (AG-II), aldosterone (AS), norepinephrine (NE), and epinephrine (EP). These indices were measured before hemodilution, after hemodilution, 80 minutes after starting hypotension, and 60 minutes after recovery from hypotension. Hemodilution alone caused no significant change in the values throughout the time course. Controlled hypotension alone caused significant increases in plasma concentrations of NE (+295%) and EP (+203%) at 80 minutes after starting hypotension, whereas it caused no change in plasma RA and plasma concentrations of AG-II and AS. Hemodilution plus controlled hypotension caused significant increases in plasma RA (+271%) and plasma concentrations of AG-II (+188%), AS (+199%), NE (+279%), and EP (+184%) at 80 minutes after starting hypotension. CONCLUSION: The combination of hemodilution and PGE1 induced controlled hypotension causes significant responses, especially in a renin-angiotensin-aldosterone system under isoflurane anesthesia.

Aged↗

PubMed1997

The endothelin ETA receptor exists in the caudal solitary tract nucleus of the rat brain.

1. The receptor autoradiographic method done on the rat lower brain stem and cerebellum plus 125I-endothelin-1, BQ-123, an antagonist for the endothelin ETA receptor, and sarafotoxin S6c, an agonist for the ETB receptor, revealed minute amounts of the ETA receptor coexisting with the ETB receptor in the caudal solitary tract nucleus of the rat lower brain stem. 2. The ETB receptor is present predominantly in other parts of the lower brain stem. 3. Knowledge of the heterogeneous distribution of the central endothelin receptor subtypes aids in understanding the neurophysiology of endothelins.

Amino Acid Sequence↗

PubMed1997

Combined effects of prolonged prostaglandin E1-induced hypotension and haemodilution on human hepatic function.

Combined effects of prolonged prostaglandin E1 (PGE1)-induced hypotension and haemodilution on hepatic function were studied in 30 patients undergoing hip surgery. The patients were randomly allocated to one of three groups; those in group A (n = 10) were subjected to controlled hypotension alone, those in group B (n = 10) to haemodilution alone and those in group C (n = 10) to both controlled hypotension and haemodilution. Haemodilution in groups B and C was produced by withdrawing approximately 1000 mL of blood and replacing it with the same amount of dextran solution, and final haematocrit values were 21 or 22%. Controlled hypotension in groups A and C was induced with PGE1 to maintain mean arterial blood pressure at 55 mmHg for 180 min. Measurements included arterial ketone body ratio (AKBR, aceto-acetate/3-hydroxybutyrate) and clinical hepatic function parameters. AKBR and biological hepatic function tests showed no change throughout the time course in groups A and B. In group C, AKBR showed a significant decrease at 120 min (-40%) and at 180 min (-49%) after the start of hypotension and at 60 min (-32%) after recovery of normotension, and SGOT, SGPT, LDH and total bilirubin showed significant increases after operation. The results suggest that a prolonged combination of more than 120 min of PGE1-induced hypotension and moderate haemodilution would cause impairment of hepatic function.

Adult↗

PubMed1997

Acute haemodilution and prostaglandin E1-induced hypotension: effects on the coagulation-fibrinolysis system.

The effects of acute haemodilution, during prostaglandin E1 (PGE1)-induced hypotension, on the blood coagulation-fibrinolysis system were studied in 40 patients undergoing hip surgery. The patients were randomly divided into four groups of 10 patients each; Group A (control) received no induced hypotension or haemodilution, group B received hypotension alone, group C received haemodilution alone and group D received the combination of induced hypotension and haemodilution. Haemodilution in groups C and D was produced by drawing approximately 1000 mL of blood and replacing it with the same amount of 6% hydroxyethyl starch. Induced hypotension in groups B and D was conducted with PGE1 and mean blood pressure was maintained at 55 mmHg. The mean dosage of PGE1 was 648 micrograms in group B and 661 micrograms in group D. In the control and PGE1-induced hypotension groups there was no significant change in platelet count (PLT), prothrombin time (PT), activated partial thromoplastin time (aPTT), fibrinogen (FIB), antithrombin-III (AT-III) or plasminogen (PLG). Haemodilution alone caused significant decreases in PLT (-43%), PT (+21%), FIB (-33%), AT-III (-21%) and PLG (-27%), and a significant increase in aPTT (+26%), whereas the combination of PGE1-induced hypotension did not cause any further change in these parameters. Serum-fibrin degradation products (FDP) significantly increased (+300%) and PLG significantly decreased (-30%) after surgery in all groups. It can be concluded that acute haemodilution to a haematocrit value of 22 +/- 2% causes a slight coagulopathy, which is not enhanced when combined with PGE1-induced hypotension.

Aged↗

PubMed1997

Effects of intravenous anesthetics on the contraction and response of rat trachea to phosphatidylinositol.

Some intravenous anaesthetics have significant effects on the tonicity of airway smooth muscle. There are evidences for a direct relationship between airway smooth muscle contraction and phosphatidylinositol (PI) response. The aims of this study were to clarify 1) the effects of anaesthetics on the cholinergically induced contraction, and 2) the relationship between the effects on the PI response and the contraction. Rat tracheal rings or slices were incubated in Krebs-Henseleit solution containing 5.5 microM carbachol (CCh) in the presence of varying doses of anaesthetics. Thiamylal, fentanyl, ketamine and midazolam all attenuated the CCh-induced contraction. On the other hand, thiamylal augmented inositol monophosphate (IP1) accumulation, whilst ketamine, midazolam and morphine did not have the effect, and fentanyl significantly attenuated IP1 accumulation. These data suggest that airway smooth muscle can be relaxed by intravenous anaesthetics, and that the relaxing effects are not always dependent on the PI system.

Analysis of Variance↗

PubMed1997

Phospholipase A2 is activated in the kidney, but not in the liver during ischemia-reperfusion.

Phospholipase A2 (PLA2) has been demonstrated to play an important role in the reperfusion injury of the kidney, gut, brain, heart and pancreas. This study was carried out to clarify whether PLA2 was involved in the ischemia-reperfusion injury of the liver. Rats were anesthetized and underwent laparotomy. They were allocated into one of 4 groups, i.e., the groups of renal ischemia (group RI), renal control (group RC), hepatic ischemia (group HI), and hepatic control (group HC). In group RI, the left renal pedicle was occluded for 1 hr, and the left kidney was removed after 1-hr reperfusion. In group HI, the portal and the hepatic artery supplying the left and middle lobes were clamped for 1 hr, followed by reperfusion. After predetermined periods of reperfusion up to 24 hr, the ischemic lobes were removed, homogenized and centrifuged. PLA2 activities in the mitochondrial fraction and the cytosolic fraction were measured with 14C-phosphatidylcholine (PC) and 14C-phosphatidylethanolamine (PE) as exogenous substrates. PLA2 activities of the both fractions in the kidney were significantly enhanced after 1-hr ischemia followed by 1-hr reperfusion. However, there was no enhancement of PLA2 activity of the either fraction in the group HI compared with the group HC. The results indicate that PLA2 is activated in the kidney but not in the liver during ischemia-reperfusion.

Alanine Transaminase↗

PubMed1997

[Effect of controlled hypotension induced by prostaglandin E1 on evoked spinal cord potential and spinal cord blood flow].

We evaluated the effect of controlled hypotension induced by PGE1 on evoked spinal cord potential (ESCP) and spinal cord blood flow (SCBF) in 14 patients undergoing laminectomy or laminoplasty. They were divided into two groups: hypotensive group (group H), non-hypotensive group (group N). Controlled hypotension was induced with PGE1 to maintain mean arterial blood pressure at 55-60 mmHg for 45 min. The amplitude and latency of the N 1 potential were analyzed, and the SCBF was estimated by laser doppler flowmeter. There were no significant differences in ESCP and SCBF. These results suggest that controlled hypotension by PGE1 maintained normal local spinal cord blood flow autoregulation.

Aged↗

PubMed1997

Superoxide generation in neutrophils from hepatic vein in patients undergoing hepatectomy.

The present study was carried out to determine whether neutrophils could be activated to increase superoxide and myeloperoxidase production during liver surgery in clinical settings. We measured superoxide production in polymorphonuclear leukocytes (PMNs) obtained from the radial artery and hepatic vein during hepatectomy. We also determined plasma myeloperoxidase (MPO) as a marker of activation of the neutrophil. Blood samples were obtained from radial artery and from hepatic vein before operation and immediately after hepatectomy. Superoxide generation in PMNs from radial artery showed no significant change during hepatectomy, while oxidant generation in PMNs from hepatic vein increased after hepatectomy (from 40.5 +/- 4.20 to 44.8 +/- 4.80 nmol/10(6) cells/30 min; p < 0.05). MPO in the plasma obtained from hepatic vein also increased significantly after hepatectomy (from 166.6 +/- 23.0 to 225.4 +/- 26.2 micrograms/L; p < 0.05). The results show that neutrophils are activated locally in the liver for enhanced release of superoxide during hepatectomy, suggesting that these oxidant species may be involved in post hepatectomy liver damage.

Adult↗

PubMed1996

Transduction of hippocampal CA1 by adenovirus in vivo.

Replication-deficient adenoviral recombinants were assessed for in vivo transduction of rat hippocampal CA1 cells. Results show that efficient widespread transduction of CA1 in vivo was rapidly achievable and was sustained for more than 5 weeks. Assessment of electrophysiological properties in acute hippocampal slices showed that synaptic functioning and mechanisms involved in long-term potentiation (LTP) were preserved for minimally 5 weeks postinfection. Hence, adenovirus-mediated gene transfer in vivo promises to be a valuable tool for dissecting molecular mechanisms of synaptic plasticity, such as LTP and long-term depression (LTD).

Adenoviruses, Human↗

PubMed1996

A conserved disulfide loop facilitates conformational maturation in the subunits of the acetylcholine receptor.

To examine the structural determinants for the assembly of ligand-gated receptors, we constructed mutant alpha, beta, gamma and delta subunits of the Torpedo acetylcholine receptor (AChR), lacking one of the conserved cysteine residues which forms a 13-amino acid disulfide loop in the amino terminal domain of each subunit. Mutant subunits were co-expressed with complementary wild-type subunits in Xenopus oocytes. Using subunit-specific antisera and monoclonal antibodies that recognize the two distinct alpha-bungarotoxin (alpha-BuTX) sites on the AChR, we were able to distinguish immature subunit associations from conformationally mature AChR complexes. Removal of the disulfide loop on the alpha subunit completely destroyed the formation of the two toxin-binding sites, while removal of the structure on the beta subunit had little effect. While mutant gamma and delta subunits were capable of forming associations (immature assembly) with other subunits, the formation of alpha-BTX sites between alpha and mutant gamma or mutant delta subunits was diminished. Interestingly, assembly of alpha beta gamma subunits remained efficient in the presence of mutant delta subunits, whereas assembly of alpha beta delta subunits was inefficient in the presence of mutant gamma subunits. Thus, these results indicate that the formation of the disulfide loop facilitates the conformational maturation of alpha gamma and alpha delta complexes, which may be conditional for correct subunit coupling in assembling receptors. Furthermore, it seems likely that the correct coupling between the alpha and gamma subunits is the most important step in subunit assembly.

Animals↗

PubMed1996

Arachidonic acid potentiates ACh receptor currents by protein kinase C activation but not by receptor phosphorylation.

The effects of arachidonic acid on ACh-gated channel currents were examined using Torpedo nicotinic ACh receptors expressed in Xenopus oocytes. Arachidonic acid decreased ACh-evoked currents during treatment, to a greater extent in Ca(2+)-free extracellular solution. The currents were enhanced for more than 30 min after washing, reaching 150 and 170% in Ca(2+)-containing and -free extracellular solutions, respectively. The current enhancement was inhibited by the selective protein kinase C (PKC) inhibitor, GF109203X, whereas the current depression was not affected. Furthermore, arachidonic acid-evoked current depression was blocked in mutant ACh receptors with PKC phosphorylation site deletions on the alpha and delta subunits, but the long-lasting potentiation effect remained. These results indicate that arachidonic acid may decrease ACh receptor currents by a direct binding to PKC phosphorylation sites of the ACh receptors and may potentiate the currents via a novel pathway related to arachidonic acid-regulated PKC activation, but not via PKC phosphorylation of the ACh receptor itself.

Animals↗

PubMed1996

Effects of hemodilution during controlled hypotension of hepatic, renal, and pancreatic function in humans.

STUDY OBJECTIVE: To evaluate the effects of hemodilution during controlled hypotension on, the hepatic renal, and pancreatic function in the clinical setting. DESIGN: Randomized, prospective study. SETTING: Inpatient surgery at Rosai Hospital. PATIENTS: 20 ASN status I and II patients scheduled for total hip arthroplasty. INTERVENTIONS: Hemodilution was carried out after induction of anesthesia, in which drawn blood was replaced with dextran solution to achieve final hematocrit (Hct) of 31% Group A = mild hemodilution group, N = 10) or 23% (Group B = moderate hemodilution group, N = 10). In both groups, controlled hypotension was induced with prostaglandin in (PGE1) to maintain mean arterial blood pressure at 55 mm Hg for 80 minutes. MEASUREMENTS AND MAIN RESULTS: Measurements included arterial ketone body ratio AKBR, aceto-acetate/3-hydroxybutyrate) for hepatic cellular function, pancreatic phospholipase A2 (P-PLA2) for pancreatic cellular function, and urine N-acetyl-beta-D-glucosaminidase (NAG index) for cellular function of the renal tubule. These indices were measured before hemodilution, after hemodilution, 80 minutes after starting hypotension, 60 minutes after recovery of normotension, and on the first postoperative day. Neither AKBR nor P-PLA2 showed a significant change throughout the time course of the study in either group. Urine-NAG index showed a significant increase in moderate hemodilution group at 60 minutes after recovery of normotension (+ 136%) and on the first postoperative lay (+ 149%) compared with prehemodilution value, whereas it showed no significant change in the mild hemodilution group. Blood urea nitrogen and serum creatinine measured postoperatively were within normal range. CONCLUSIONS: PGE1 induced hypotension combined with moderate hemodilution using dextran, such as 23% of Net value maintains hepatic and pancreatic function but causes damage to the renal tubular cells.

3-Hydroxybutyric Acid↗

PubMed1996

Anticholinesterase drugs stimulate phosphatidylinositol response in rat tracheal slices.

Some anticholinesterase (anti-ChE) drugs induce airway smooth muscle contraction. Whether anti-ChE drugs stimulate muscarinic receptors in airway smooth muscle as well as nicotinic receptors in neuromuscular junction is unknown. Since there is a direct relationship between phosphatidylinositol (PI) response and airway smooth muscle contraction induced by muscarinic agonists, we examined the effects of neostigmine, physostigmine, pyridostigmine, and edrophonium on PI response in the airway smooth muscle. The rat tracheal slices were incubated in Krebs-Henseleit solution containing LiCl and [3H]myo-inositol in the presence of carbachol, anti-ChE, or none of them. [3H]inositol monophosphate (IP1), which is a degradation product of PI response, was counted with a liquid scintillation counter. Inositol monophosphate accumulation was stimulated by neostigmine, physostigmine, and pyridostigmine in a dose-dependent manner, but was not affected by edrophonium. These increases were completely inhibited by atropine. The results suggest that neostigmine, physostigmine, and pyridostigmine stimulate PI response in the airway smooth muscle, which would cause bronchoconstriction, while edrophonium does not affect PI response.

Animals↗