Biomedical subjects

Tom Schilling

Publications and source records attributed to Tom Schilling.

6 recordsLinked to original sources

PubMed2006

Lysophosphatidylcholine stimulates IL-1beta release from microglia via a P2X7 receptor-independent mechanism.

IL-1beta released from activated macrophages contributes significantly to tissue damage in inflammatory, degenerative, and autoimmune diseases. In the present study, we identified a novel mechanism of IL-1beta release from activated microglia (brain macrophages) that occurred independently of P2X(7) ATP receptor activation. Stimulation of LPS-preactivated microglia with lysophosphatidylcholine (LPC) caused rapid processing and secretion of mature 17-kDa IL-1beta. Neither LPC-induced IL-1beta release nor LPC-stimulated intracellular Ca(2+) increases were affected by inhibition of P2X(7) ATP receptors with oxidized ATP. Microglial LPC-induced IL-1beta release was suppressed in Ca(2+)-free medium or during inhibition of nonselective cation channels with Gd(3+) or La(3+). It was also attenuated when Ca(2+)-activated K(+) channels were blocked with charybdotoxin (CTX). The electroneutral K(+) ionophore nigericin did not reverse the suppressive effects of CTX on LPC-stimulated IL-1beta release, demonstrating the importance of membrane hyperpolarization. Furthermore, LPC-stimulated caspase activity was unaffected by Ca(2+)-free medium or CTX, suggesting that secretion but not processing of IL-1beta is Ca(2+)- and voltage-dependent. In summary, these data indicate that the activity of nonselective cation channels and Ca(2+)-activated K(+) channels is required for optimal IL-1beta release from LPC-stimulated microglia.

Animals↗

PubMed2004

A novel physiological mechanism of glycine-induced immunomodulation: Na+-coupled amino acid transporter currents in cultured brain macrophages.

Glycine is known to modulate immune cell responses. However, the physiological mechanisms underlying inhibitory effects of glycine on macrophages are not well understood. Here we show that glycine is capable of inducing inward currents in brain macrophages (microglia). In contrast to glycine, the glycine receptor agonist taurine failed to elicit currents. Glycine-evoked currents of brain macrophages were unaffected by strychnine, Cl(-)-free extracellular solution, N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl])sarcosine (NFPS) and amoxapine, but were abolished upon omission of extracellular Na(+). Furthermore, glycine caused increases in the intracellular Na(+) concentration and pronounced membrane depolarization. Glycine-evoked depolarization was Na(+) dependent and occurred independently of the intracellular Cl(-) concentration. Similarly to glycine, glutamine and alpha-(methylamino)isobutyric acid (MeAIB) elicited inward currents in brain macrophages. In the presence of either glutamine or MeAIB, glycine-induced currents were inhibited. It is concluded that neither functional glycine receptors nor glycine transporters are expressed in brain macrophages. We suggest that glycine mediates its effects by activation of system A Na(+)-coupled neutral amino acid transporters.

Amino Acid Transport Systems, Neutral↗

PubMed2004

Physiological mechanisms of lysophosphatidylcholine-induced de-ramification of murine microglia.

Activation of microglial cells, the resident macrophages of the brain, occurs rapidly following brain injury. De-ramification, i.e. transformation from ramified into amoeboid morphology is one of the earliest manifestations of microglial activation. In the present study, we identified the physiological mechanisms underlying microglial de-ramification induced by lysophosphatidylcholine (LPC). Patch-clamp experiments revealed activation of non-selective cation currents and Ca(2+)-dependent K(+) currents by extracellular LPC. LPC-activated non-selective cation channels were permeable for monovalent and divalent cations. They were inhibited by Gd(3+), La(3+), Zn(2+) and Grammostola spatulata venom, but were unaffected by diltiazem, LOE908MS, amiloride and DIDS. Ca(2+) influx through non-selective cation channels caused sustained increases in intracellular Ca(2+) concentration. These Ca(2+) increases were sufficient to elicit charybdotoxin-sensitive Ca(2+)-dependent K(+) currents. However, increased [Ca(2+)](i) was not required for LPC-induced morphological changes. In LPC-stimulated microglial cells, non-selective cation currents caused transient membrane depolarization, which was followed by sustained membrane hyperpolarization induced by Ca(2+)-dependent K(+) currents. Furthermore, LPC elicited K(+) efflux by stimulating electroneutral K(+)-Cl(-) cotransporters, which were inhibited by furosemide and DIOA. LPC-induced microglial de-ramification was prevented by simultaneous inhibition of non-selective cation channels and K(+)-Cl(-) cotransporters, suggesting their functional importance for microglial activation.

Algorithms↗

PubMed2004

Functional importance of Ca2+-activated K+ channels for lysophosphatidic acid-induced microglial migration.

Abstract Migration of microglial cells towards damaged tissue plays a key role in central nervous system regeneration under pathological conditions. Using time lapse video microscopy we show that lysophosphatidic acid (LPA) enhances chemokinetic migration of murine microglial cells. In the presence of 1 micro m LPA, the mean migration rate of microglial cells was increased 3.8-fold. In patch-clamp studies we demonstrate that LPA induces activation of a Ca(2+)-activated K(+) current. Microglial Ca(2+)-activated K(+) currents were abolished by either 50 nm charybdotoxin or 10 micro m clotrimazole. In contrast, 5 micro m paxilline did not have any significant effects on Ca(2+)-activated K(+) currents. The LPA-stimulated migration of microglial cells was inhibited by blockers of IKCa1 Ca(2+)-activated K(+) channels. The mean migration rate of LPA-stimulated cells was decreased by 61% in the presence of 50 nm charybdotoxin or by 51% during exposure to 10 micro m clotrimazole. Microglial migration was not inhibited by 5 micro m paxilline. It is concluded that IKCa1 Ca(2+)-activated K(+) channels are required for LPA-stimulated migration of microglial cells.

Animals↗

PubMed2003

Effects of kinase inhibitors on TGF-beta induced upregulation of Kv1.3 K+ channels in brain macrophages.

Deactivation of brain macrophages (microglia) by transforming growth factor-beta (TGF-beta) is characterized by enhanced Kv1.3 K+ channel expression. The intracellular mechanisms by which TGF-beta causes K+ channel upregulation in microglia have remained unclear. We show here that the protein kinase inhibitor H7 abolishes TGF-beta-induced increases in delayed rectifier K+ current density. However, this effect cannot be related to inhibition of protein kinase C (PKC) or protein kinase A (PKA) activity, because specific PKC and PKA inhibitors did not exhibit effects identical to H7. TGF-beta-induced Kv1.3 channel expression was also unaffected by inhibitors of tyrosine kinase, Ca2+/calmodulin kinase II and mitogen-activated protein (MAP) kinase ERK. In contrast, delayed rectifier K+ current density was larger in TGF-beta-stimulated cells pretreated with the p38 MAP kinase inhibitor SB203580 or the phosphatidylinositol 3-OH (PI3) kinase inhibitor wortmannin, suggesting that both p38 MAP kinase and PI3 kinase regulate negatively the upregulation of Kv1.3 K+ channels in TGF-beta-treated microglial cells.

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

PubMed2002

Voltage-activated proton currents in human lymphocytes.

Voltage-activated proton currents are reported for the first time in human peripheral blood T and B lymphocytes and in the human leukaemic T cell line Jurkat E6-1. The properties of H(+) currents studied using tight-seal voltage-clamp recording techniques were similar in all cells. Changing the pH gradient by one unit caused a 47 mV shift in the reversal potential, demonstrating high selectivity of the channels for protons. H(+) current activation upon membrane depolarisation had a sigmoidal time course that could be fitted by a single exponential function after a brief delay. Increasing pH(o) shifted the activation threshold to more negative potentials, and increased both the H(+) current amplitude and the rate of activation. In lymphocytes studied at pH(i) 6.0, the activation threshold was more negative and the H(+) current density was three times larger than at pH(i) 7.0. Increasing the intracellular Ca(2+) concentration to 1 microM did not change H(+) current amplitude or kinetics detectably. Extracellularly applied Zn(2+) and Cd(2+) inhibited proton currents, slowing activation and shifting the voltage-activation curve to more positive potentials. The H(+) current amplitude was 100 times larger in CD19+ B lymphocytes and in Jurkat E6-1 cells than in CD3+ T lymphocytes. Following stimulation with the phorbol ester PMA, the H(+) current density in peripheral blood T lymphocytes and Jurkat T cells increased. In contrast, the H(+) current density of phorbol ester (PMA)-stimulated B lymphocytes was reduced and activation became slower. The pattern of expression of H(+) channels in lymphocytes appears well suited to their proposed role of charge compensation during the respiratory burst.

B-Lymphocytes↗