A "synaptoplasmic cistern" mediates rapid inhibition of cochlear hair cells

Cochlear hair cells are inhibited by cholinergic efferent neurons. The acetylcholine (ACh) receptor of the hair cell is a ligand-gated cation channel through which calcium enters to activate potassium channels and hyperpolarize the cell. It has been proposed that calcium-induced calcium release (CICR) from a near-membrane postsynaptic store supplements this process. Here, we demonstrate expression of type I ryanodine receptors in outer hair cells in the apical turn of the rat cochlea. Consistent with this finding, ryanodine and other store-active compounds alter the amplitude of transient currents produced by synaptic release of ACh, as well as the response of the hair cell to exogenous ACh. Like the sarcoplasmic reticulum of muscle, the "synaptoplasmic" cistern of the hair cell efficiently couples synaptic input to CICR.Fil: Lioudyno, Maria. Johns Hopkins University School of Medicine; Estados UnidosFil: Hiel, Hakim. Johns Hopkins University School of Medicine; Estados UnidosFil: Kong, Jee-Hyun. Johns Hopkins University School of Medicine; Estados UnidosFil: Katz, Eleonora. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Waldman, Erik. Johns Hopkins University School of Medicine; Estados UnidosFil: Parameshwaran Iyer, Suchitra. Johns Hopkins University School of Medicine; Estados UnidosFil: Glowatzki, Elisabeth. Johns Hopkins University School of Medicine; Estados UnidosFil: Fuchs, Paul A.. Johns Hopkins University School of Medicine; Estados Unido

Suppressing Aneuploidy-Associated Phenotypes Improves the Fitness of Trisomy 21 Cells

An abnormal number of chromosomes, or aneuploidy, accounts for most spontaneous abortions, causes developmental defects, and is associated with aging and cancer. The molecular mechanisms by which aneuploidy disrupts cellular function remain largely unknown. Here, we show that aneuploidy disrupts the morphology of the nucleus. Mutations that increase the levels of long-chain bases suppress nuclear abnormalities of aneuploid yeast independent of karyotype identity. Quantitative lipidomics indicates that long-chain bases are integral components of the nuclear membrane in yeast. Cells isolated from patients with Down syndrome also show that abnormal nuclear morphologies and increases in long-chain bases not only suppress these abnormalities but also improve their fitness. We obtained similar results with cells isolated from patients with Patau or Edward syndrome, indicating that increases in long-chain bases improve the fitness of aneuploid cells in yeast and humans. Targeting lipid biosynthesis pathways represents an important strategy to suppress nuclear abnormalities in aneuploidy-associated diseases

STIM1, an essential and conserved component of store-operated Ca2+ channel function

Store-operated Ca2+ (SOC) channels regulate many cellular processes, but the underlying molecular components are not well defined. Using an RNA interference (RNAi)-based screen to identify genes that alter thapsigargin (TG)-dependent Ca2+ entry, we discovered a required and conserved role of Stim in SOC influx. RNAi-mediated knockdown of Stim in Drosophila S2 cells significantly reduced TG-dependent Ca2+ entry. Patch-clamp recording revealed nearly complete suppression of the Drosophila Ca2+ release-activated Ca2+ (CRAC) current that has biophysical characteristics similar to CRAC current in human T cells. Similarly, knockdown of the human homologue STIM1 significantly reduced CRAC channel activity in Jurkat T cells. RNAi-mediated knockdown of STIM1 inhibited TG- or agonist-dependent Ca2+ entry in HEK293 or SH-SY5Y cells. Conversely, overexpression of STIM1 in HEK293 cells modestly enhanced TG-induced Ca2+ entry. We propose that STIM1, a ubiquitously expressed protein that is conserved from Drosophila to mammalian cells, plays an essential role in SOC influx and may be a common component of SOC and CRAC channels

Shaker-Related Potassium Channels in the Central Medial Nucleus of the Thalamus Are Important Molecular Targets for Arousal Suppression by Volatile General Anesthetics

The molecular targets and neural circuits that underlie general anesthesia are not fully elucidated. Here, we directly demonstrate that Kv1-family (Shaker-related) delayed rectifier K(+) channels in the central medial thalamic nucleus (CMT) are important targets for volatile anesthetics. The modulation of Kv1 channels by volatiles is network specific as microinfusion of ShK, a potent inhibitor of Kv1.1, Kv1.3, and Kv1.6 channels, into the CMT awakened sevoflurane-anesthetized rodents. In heterologous expression systems, sevoflurane, isoflurane, and desflurane at subsurgical concentrations potentiated delayed rectifier Kv1 channels at low depolarizing potentials. In mouse thalamic brain slices, sevoflurane inhibited firing frequency and delayed the onset of action potentials in CMT neurons, and ShK-186, a Kv1.3-selective inhibitor, prevented these effects. Our findings demonstrate the exquisite sensitivity of delayed rectifier Kv1 channels to modulation by volatile anesthetics and highlight an arousal suppressing role of Kv1 channels in CMT neurons during the process of anesthesia

STIM1, an Essential and Conserved Component of Store-Operated Ca\u3csup\u3e2+\u3c/sup\u3e Channel Function

Store-operated Ca2+ (SOC) channels regulate many cellular processes, but the underlying molecular components are not well defined. Using an RNA interference (RNAi)-based screen to identify genes that alter thapsigargin (TG)-dependent Ca2+ entry, we discovered a required and conserved role of Stim in SOC influx. RNAi-mediated knockdown of Stim in Drosophila S2 cells significantly reduced TG-dependent Ca2+ entry. Patch-clamp recording revealed nearly complete suppression of the Drosophila Ca2+ release-activated Ca2+(CRAC) current that has biophysical characteristics similar to CRAC current in human T cells. Similarly, knockdown of the human homologue STIM1 significantly reduced CRAC channel activity in Jurkat T cells. RNAi-mediated knockdown of STIM1 inhibited TG- or agonist-dependent Ca2+ entry in HEK293 or SH-SY5Y cells. Conversely, overexpression of STIM1 in HEK293 cells modestly enhanced TG-induced Ca2+ entry. We propose that STIM1, a ubiquitously expressed protein that is conserved from Drosophila to mammalian cells, plays an essential role in SOC influx and may be a common component of SOC and CRAC channels

Direct interaction of serotonin type 3 receptor ligands with recombinant and native α9α10-containing nicotinic cholinergic receptors

In the present work, we characterized the effects of serotonin type 3 receptor ligands on recombinant and native α9α10-containing nicotinic acetylcholine receptors (nAChRs). Our results indicate that the recombinant α9α10 nAChR shares striking pharmacological properties with 5-HT3 ligand-gated ion channels. Thus, 5-HT3 receptor antagonists block ACh-evoked currents in α9α10-injected Xenopus laevis oocytes with a rank order of potency of tropisetron (IC50, 70.1 ± 0.9 nM) > ondansetron (IC50, 0.6 ± 0.1 μM) = MDL 72222 (IC50, 0.7 ± 0.1 μM). Although serotonin does not elicit responses in α9α10-injected oocytes, it blocks recombinant α9α10 receptors in a noncompetitive and voltage-dependent manner (IC50, 5.4 ± 0.6 μM). On the other hand, we demonstrate an in vivo correlate of these properties of the recombinant receptor, with those of the α9α10-containing nAChR of frog saccular hair cells. The possibility that the biogenic amine serotonin might act as a neuromodulator of the cholinergic efferent transmission in the vestibular apparatus and in the organ of Corti is discussed.Fil: Rothlin, Carla. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Lioudyno, Maria I.. Tulane University; Estados UnidosFil: Silbering, Ana F.. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Plazas, Paola Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Gomez Casati, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Katz, Eleonora. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Guth, Paul S.. Tulane University; Estados UnidosFil: Elgoyhen, Ana Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentin