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Biomedical subjects

S C Ahn

Publications and source records attributed to S C Ahn.

30 records · Page 2Linked to original sources

Dyskinesias subside off all medication in a boy with autistic disorder and severe mental retardation.

A boy with autistic disorder and severe mental retardation developed severe dyskinesias, including objective akathisia (probable) and tics, a month after discontinuation of at least two years of treatment with drugs block dopamine receptors. These dyskinesias greatly subsided during a 17-wk. open-label nonblind clinical trial of clomipramine, and returned transiently when the parents abruptly discontinued clomipramine. However, the dyskinesias gradually subsided during two and a half years of follow-up with the boy being off all medication. A few stereotypies remain. We believe this suggests the hypothesis that movement disorders, such as withdrawal and tardive akathisia and tics, occurring in boys with autistic disorder treated with dopamine receptor-blocking drugs may subside months or years after discontinuation of the agents and that clomipramine may facilitate this process. We also hypothesize that some boys with autistic disorder and mental retardation exhibit fewer movement disorders, fewer psychiatric symptoms, and better over-all functioning after they have received no dopamine receptor-blocking drugs for several months, and this improvement continues years after the medication has ceased.

Akathisia, Drug-Induced↗

Inhibition of PDGF-induced phospholipase C activation by herbimycin A.

Herbimycin A, an inhibitor of protein tyrosine kinases, dose-dependently reduced PDGF-induced inositol phosphates (IPt) accumulation without effect on phosphatidylethanol (PEt) formation in PLC-gamma 1-overexpressing NIH 3T3 (NIH 3T3 gamma 1) cells. The compound also reduced tyrosine phosphorylations of some proteins including PLC-gamma 1 in response to PDGF. On the other hand, phorbol 12-myristate 13-acetate (PMA)-induced phospholipase D (PLD) activation was reduced by herbimycin A in the cells, indicating that the pathways for PLD activation by PDGF and PMA are different from each other. Also, these results suggest that PLC-gamma 1 activation is not always an upstream event for PLD activation and that tyrosine phosphorylation of one or more proteins not affected by herbimycin A should be indispensable for PLD activation in PDGF-stimulated NIH 3T3 gamma 1 cells.

3T3 Cells↗

Inhibition of phospholipase C gamma 1 activity by amentoflavone isolated from Selaginella tamariscina.

Amentoflavone was isolated as an inhibitor of phospholipase C gamma 1 (PLC gamma 1) and phosphoinositides (PI)-turnover in PLC gamma 1 overexpressing NIH3T3 fibroblasts (NIH3T3 gamma 1) from Selaginella tamariscina (Selaginellaceae) together with other related biflavonoids, isocryptomerin and cryptomerin B. Only amentoflavone inhibited the PLC gamma 1 activity with an IC50 of 29 microM and the formation of total inositol phosphates (IPt) in PDGF-stimulated NIH3T3 gamma 1 with an IC50 of 9.2 microM but did not show inhibitor activity against protein kinase C. Isocryptomerin and cryptomerin B did not show inhibitor activity against PLC gamma 1 at the concentration of 150 microM, and did not inhibit IPt production in PDGF-induced NIH3T3 gamma 1 at the concentration of 180 microM.

3T3 Cells↗

Secretion of Bacillus alpha-amylase from yeast directed by glucoamylase I signal sequence of Saccharomyces diastaticus.

For the secretion of Bacillus stearothermophilus alpha-amylase from yeast, a recombinant plasmid pGAT17 was constructed by fusing B. stearothermophilus alpha-amylase structural gene in frame to the promoter and signal sequence of Saccharomyces diastaticus glucoamylase I gene (STA1). The secretion of the heterologous alpha-amylase from S. diastaticus transformed with pGAT17 was confirmed by the halo formation around colonies on selective starch agar medium. About 80% of the total alpha-amylase activity was detected in the extracellular culture medium. The secreted alpha-amylase was glycosylated and its molecular weight increased from 61 kDa to 75 kDa. The thermostability of the the glycosylated alpha-amylase was markedly enhanced, compared with that of the non-glycosylated enzyme from E. coli.

Amino Acid Sequence↗

Inhibition of PDGF-induced phospholipase D but not phospholipase C activation by herbimycin A.

It is known that PDGF-induced phospholipase D (PLD) activation occurs downstream of phospholipase C gamma 1 (PLC-gamma 1) activation. Herbimycin A, a specific inhibitor of Src family tyrosine kinase, dose-dependently inhibited PDGF-induced PLD activation (IC50 of 8 micrograms/ml) without affecting PLC-gamma 1 activation and significantly reduced PDGF-induced tyrosine phosphorylations of 40-46 kD and 60 kD proteins in PLC-gamma 1-overexpressing NIH 3T3 gamma 1 cells. These results suggest that PLC activation is necessary but not sufficient for PDGF-induced PLD activation. Tyrosine phosphorylation of p40-p46 and p60 is thought to be involved in PDGF-induced activation of PLD but not of PLC.

3T3 Cells↗

Role of calmodulin in the activation of carbachol-activated cationic current in guinea-pig gastric antral myocytes.

In mammalian gastrointestinal myocytes, it is known that muscarinic stimulation activates nonselective cation channels through a G-protein and a Ca2+-dependent pathway. We recorded inward cationic currents following application of carbachol (ICCh) to guinea-pig gastric myocytes, which were held at -20 mV using the whole-cell patch-clamp method. ICCh was suppressed by nicardipine or removal of Ca2+ from the bath solution. The peak value of inward current induced by repetitive applications of carbachol (CCh) decreased progressively (run-down phenomenon). This run-down was significantly alleviated by the addition of calmodulin to the pipette solution (0.15 mg/ml) or by using the perforated-patch whole-cell voltage-clamp technique. Moreover, W-7[N-6(aminohexyl)-5-chloro-1-naphthalenesulphonamide], a calmodulin antagonist, was a reversible inhibitor of ICCh. However, @-7 had only a weak inhibitory effect on the same cationic current which was induced by guanosine 5'-O-(3-thiotriphosphate) (GTP¿gammaS] 0.2 mM) in the pipette solution. This GTP[gammaS]-induced cationic current was still markedly suppressed by the Ca2+-free bath solution. W-7 itself had a weak inhibitory effect on voltage-operated Ca2+ channels as well as the effects on ICCh. These data suggest that multiple Ca2+-dependent pathways are involved in the activation of CCh-gated cation channels in guinea-pig antral myocytes and a Ca2+/calmodulin-dependent pathway would be one of them.

Animals↗

Quinidine blockade of the carbachol-activated nonselective cationic current in guinea-pig gastric myocytes.

1. In guinea-pig gastric myocytes isolated from the antral circular layer, stimulation of muscarinic receptors by carbachol (CCh) induces a cationic current (ICCh) which is known as the main mechanism of depolarization induced by muscarinic stimulation. 2. We tested the effects of a number of ion channel blockers on ICCh and focused upon quinidine which was a highly potent blocker. Externally applied quinidine suppressed ICCh (IC50 = 0.25 microM) in a reversible and voltage-dependent manner. Applied internally, quinidine was about 100 times less potent than when applied externally. Persistent activation of G-protein by GTP gamma S also induced a cationic current similar to ICCh and this current was also blocked by quinidine. 4-Aminopyridine and tetraethylammonium also suppressed ICCh in a dose-dependent manner (IC50 = 3.3 mM and 4.1 mM, respectively). 3. Pretreatment with quinidine (2 microM) selectively blocked the acetylcholine (ACh)-induced depolarization which was recorded in the multicellular tissues by a conventional intracellular microelectrode technique. 4. Voltage-dependent K-currents were also suppressed by quinidine but in a higher concentration range (IC50 = 3 microM). Quinidine, 10 microM, decreased the amplitude of the voltage-dependent Ca current to only a small extent (15% decrease at 0 mV). Quinidine, 2 microM, also suppressed only a minute proportion of the Ca-activated K current (11.1% decrease at 45 mV). 5. From these experiments, it is concluded that some organic agents known as K channel blockers are able to block the CCh-activated cation channel in a non-specific manner and among them, quinidine can be used as an effective blocker for ICCh in guinea-pig gastric myocytes.

4-Aminopyridine↗

Inhibition of PDGF-induced phosphoinositide-turnover by glucopiericidin A.

In the search for a substance which would specifically block a particular step in the signal transduction cascade, we identified glucopiericidin A produced by Streptomyces sp. as an inhibitor of phosphoinositide (PI)-turnover in phospholipase-Cgamma1 (PLC-gamma1) overexpressing NIH 3T3 fibroblasts (NIH 3T3gamma1). Glucopiericidin A inhibited the formation of inositol phosphate (IPt) in platelet-derived growth factor (PDGF)-stimulated NIH 3T3gamma1 cells with an IC50 of 5.0 microM. In vitro enzyme assay showed the compound had no inhibitory effect on PLC-gamma1 even at 100 microM concentration. Glucopiericidin A reduced PDGF-induced tyrosine phosphorylations of proteins, including PDGF receptor and PLC-gamma1, in the cells. In contrast, glucopiericidin A showed only a slight inhibitory effect on epidermal growth factor (EGF)-induced IPt production and protein tyrosine phosphorylations in A431 cells. These results suggest that glucopiericidin A inhibits PDGF-induced activation of PLC-gamma1 by reducing the tyrosine kinase activity of the PDGF receptor and it more potently inhibits PI-turnover induced by PDGF than by EGF.

3T3 Cells↗

Effects of purinergic agonists on mechanical and electrical activities of gastric smooth muscle of guinea-pig.

The effects of purinergic agonists on the mechanical and electrical activity of antral circular muscle of guinea-pig stomach were investigated. ATP potentiated the mechanical contraction without any change in membrane potential. To characterize the purinoceptors involved, effects of ATP analogues, especially P2X or P2Y receptor agonists, were studied. 2-MethylthioATP (2-MeSATP), a P2Y agonist, showed the same effects as that of ATP. On the other hand, a P2X agonists, alpha, beta-methyleneATP (alpha, beta-MeATP) incuced relaxation with hyperpolarization. At the holding potential of 0 mV, spontaneous transient outward currents (STOCs) were recorded in whole-cell mode. Externally applied ATP revealed transient increase of STOCs. Considering that STOCs reflect the changes of internal Ca2+, these results might be explained by the transient increase of internal Ca2+ release from internal Ca2+ store. From these results, it is concluded that there are at least two types of purinoceptors in guinea-pig stomach, and contractile response via P2Y-purinoceptor might be related to the elevation of internal Ca2+ released from internal Ca2+ store.

Adenosine Triphosphate↗

Effect of intracellular cAMP on K current in single gastric myocytes of guinea-pig.

In guinea-pig stomach, the effect of increased intracellular cAMP induced by forskolin, 8-Br-cAMP, or isobuthyl-methylxanthine (IBMX) on K current was studied in whole-cell currents. In enzymatically dispersed single cells, agents elevating [cAMP]in showed quite different effects on the IK depending on the recording conditions. Though using the same recording pipette containing 0.1 mM EGTA, agents elevating [cAMP]in reduced IK(Ca) recorded at various membrane potentials, while forskolin increased the spontaneous transient outward currents (STOCs) recorded at fixed holding potential, 0 mV. Such a reduction of K currents was not observed in the cells dialysed with heparin contained in the recording pipette. These results suggested the possibility that the cAMP modulate the internal Ca(2+)-store. To assess the effect of cAMP on the internal Ca2+ store, carbachol or caffeine was used to mobilize intracellular Ca2+ store. Using the carbachol- or caffeine-induced IK(Ca), the effects of forskolin on [Ca2+]in was investigated. Forskolin inhibited the carbachol-induced K current, while the caffeine-induced current was not affected. From the above results, it might be suggested that increased intracellular cAMP might modulate the release of Ca2+ from IP3-sensitive Ca2+ store to- reduce the Ca(2+)-activated K currents.

Animals↗

Cellular distributions of the prohormone processing enzymes PC1 and PC2.

The prohormone convertases PC1 (also known as sPC3) and PC2 are known to mediate the proteolytic conversion of inactive neuropeptide and hormone precursors to bioactive peptide products. In this study we have used sucrose density centrifugation to determine the subcellular distributions of the various forms of PC1 and PC2 in three different cell types, AtT-20, beta TC3, and PC12 cells. The former two cell lines naturally express PC enzymes, while PC12 cell clones expressing PCs were obtained by stable transfection. Our data show considerable cell-line specific variation in PC processing, with PC12 cells exhibiting the most complete processing of both enzyme precursors. While in all cell lines mature forms of both enzymes were stored within particles having the same buoyant density as secretory granule markers, in some cell lines substantial amounts of mature PC1 and PC2 were also associated with the Golgi marker. Processing of the two PC precursors was not interdependent since PC12 cells expressing only one of the two PCs were fully capable of enzyme maturation. Interestingly, analysis of intracellular processing of an endogenous peptide precursor, proneurotensin, revealed that transfected PC1, but not PC2, showed enzymatic activity against this precursor.

Animals↗