Youngeun Han

Costimulation of AMPA and metabotropic glutamate receptors underlies phospholipase C activation by glutamate in hippocampus.

Glutamate, a major neurotransmitter in the brain, activates ionotropic and metabotropic glutamate receptors (iGluRs and mGluRs, respectively). The two types of glutamate receptors interact with each other, as exemplified by the modulation of iGluRs by mGluRs. However, the other way of interaction (i.e., modulation of mGluRs by iGluRs) has not received much attention. In this study, we found that group I mGluR-specific agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) alone is not sufficient to activate phospholipase C (PLC) in rat hippocampus, while glutamate robustly activates PLC. These results suggested that additional mechanisms provided by iGluRs are involved in group I mGluR-mediated PLC activation. A series of experiments demonstrated that glutamate-induced PLC activation is mediated by mGluR5 and is facilitated by local Ca2+ signals that are induced by AMPA-mediated depolarization and L-type Ca2+ channel activation. Finally, we found that PLC and L-type Ca2+ channels are involved in hippocampal mGluR-dependent long-term depression (mGluR-LTD) induced by paired-pulse low-frequency stimulation, but not in DHPG-induced chemical LTD. Together, we propose that AMPA receptors initiate Ca2+ influx via the L-type Ca2+ channels that facilitate mGluR5-PLC signaling cascades, which underlie mGluR-LTD in rat hippocampus.

Rac-mediated actin remodeling and myosin II are involved in KATP channel trafficking in pancreatic β-cells.

AMP-activated protein kinase (AMPK) is a metabolic sensor activated during metabolic stress and it regulates various enzymes and cellular processes to maintain metabolic homeostasis. We previously reported that activation of AMPK by glucose deprivation (GD) and leptin increases KATP currents by increasing the surface levels of KATP channel proteins in pancreatic β-cells. Here, we show that the signaling mechanisms that mediate actin cytoskeleton remodeling are closely associated with AMPK-induced KATP channel trafficking. Using F-actin staining with Alexa 633-conjugated phalloidin, we observed that dense cortical actin filaments present in INS-1 cells cultured in 11 mM glucose were disrupted by GD or leptin treatment. These changes were blocked by inhibiting AMPK using compound C or siAMPK and mimicked by activating AMPK using AICAR, indicating that cytoskeletal remodeling induced by GD or leptin was mediated by AMPK signaling. AMPK activation led to the activation of Rac GTPase and the phosphorylation of myosin regulatory light chain (MRLC). AMPK-dependent actin remodeling induced by GD or leptin was abolished by the inhibition of Rac with a Rac inhibitor (NSC23766), siRac1 or siRac2, and by inhibition of myosin II with a myosin ATPase inhibitor (blebbistatin). Immunocytochemistry, surface biotinylation and electrophysiological analyses of KATP channel activity and membrane potentials revealed that AMPK-dependent KATP channel trafficking to the plasma membrane was also inhibited by NSC23766 or blebbistatin. Taken together, these results indicate that AMPK/Rac-dependent cytoskeletal remodeling associated with myosin II motor function promotes the translocation of KATP channels to the plasma membrane in pancreatic β-cells.

A new species of Clytus Laicharting (Coleoptera: Cerambycidae) from Korea with a key to Korean species

A new species of Clytus Laicharting (Coleoptera: Cerambycidae) is described from Korea. Illustrations of diagnostic characteristics of the new species including male genitalia are provided with a key to Korean Clytus species.

Taxonomic Review of the Genus Xylotrechus (Coleoptera: Cerambycidae: Cerambycinae) in Korea with a Newly Recorded Species

A total of sixteen Xylotrechus species from the Korean peninsula are recognized, including a newly recorded species, Xylotrechus pavlovskii Plavilstshikov, 1954. We present brief descriptions of the Korean Xylotrechus species, except four species which could not be examined in this study. The geographic distribution, host plants, illustrations for each species, and a key to the Korean Xylotrechus species are provided.

A study on the characteristics of (Ti1−xAlx)N coatings deposited by plasma-enhanced chemical vapor deposition after heat treatment

Abstract (Ti 1− x Al x )N films were deposited on M2 high-speed steel (HSS) and α-Al 2 O 3 substrates by a plasma-enhanced chemical vapor deposition (PECVD) process, and the change in hardness and the phase transformation of the coatings after heat treatment were examined. The hardness of the (Ti 1− x Al x )N coatings deposited on HSS increased with increasing heat treatment time at 1100 °C, reaching a maximum hardness. Further increases in heat treatment time led to a decrease in hardness. However, the hardness of the (Ti 1− x Al x )N coatings deposited on alumina substrates decreased slightly after heat treatment. XRD and TEM analysis indicated that the hardness change of the (Ti 1− x Al x )N coatings after heat treatment is related to the precipitation of a stable wurzite AlN phase from the metastable NaCl-(Ti 1− x Al x ) phases. Moreover, this precipitation effect depends on the Al content and the grain size of the as-deposited coating.

Ca 2+ clearance by plasmalemmal NCLX, Li + -permeable Na + /Ca 2+ exchanger, is required for the sustained exocytosis in rat insulinoma INS-1 cells

Na+/Ca2+ exchangers are key players for Ca2+ clearance in pancreatic β-cells, but their molecular determinants and roles in insulin secretion are not fully understood. In the present study, we newly discovered that the Li+-permeable Na+/Ca2+ exchangers (NCLX), which were known as mitochondrial Na+/Ca2+ exchangers, contributed to the Na+-dependent Ca2+ movement across the plasma membrane in rat INS-1 insulinoma cells. Na+/Ca2+ exchange activity by NCLX was comparable to that by the Na+/Ca2+ exchanger, NCX. We also confirmed the presence of NCLX proteins on the plasma membrane using immunocytochemistry and cell surface biotinylation experiments. We further investigated the role of NCLX on exocytosis function by measuring the capacitance increase in response to repetitive depolarization. Small interfering (si)RNA-mediated downregulation of NCLX did not affect the initial exocytosis, but significantly suppressed sustained exocytosis and recovery of exocytosis. XIP (NCX inhibitory peptide) or Na+ replacement for inhibiting Na+-dependent Ca2+ clearance also selectively suppressed sustained exocytosis. Consistent with the idea that sustained exocytosis requires ATP-dependent vesicle recruitment, mitochondrial function, assessed by mitochondrial membrane potential (ΔΨ), was impaired by siNCLX or XIP. However, depolarization-induced exocytosis was hardly affected by changes in intracellular Na+ concentration, suggesting a negligible contribution of mitochondrial Na+/Ca2+ exchanger. Taken together, our data indicate that Na+/Ca2+ exchanger-mediated Ca2+ clearance mediated by NCLX and NCX is crucial for optimizing mitochondrial function, which in turn contributes to vesicle recruitment for sustained exocytosis in pancreatic β-cells.

Record of Coptoclerus Chapin from Korea with a new species and a note on the distribution of the genus (Coleoptera: Cleridae)

Abstract A new species of Coptoclerus Chapin (Coleoptera: Cleridae), C. quadrimaculatus Lim sp. nov., is described from Korea. Coptoclerus is reported from the country for the first time. The new species differs from congeners in having the following characteristics: head and the prothorax black; each elytron with two separated black maculations and a transverse thick black band on the middle of disc; rasp-like punctures on the basal third of the elytral disc, punctures denser and bigger in basal third than in apical two-thirds. Description, diagnostic illustrations of the new species and additional morphological characteristics of a closely related species, C. gressitti Miyatake, are provided with a distribution map of each species of Coptoclerus.