The action of prostaglandins on ion channels.

Prostaglandins, in particular PGE(2) and prostacyclin PGI(2) have diverse biological effects. Most importantly, they are involved in inflammation and pain. Prostaglandins in nano- and micromolar concentrations sensitize nerve cells, i.

Arachidonic acid and ion channels: an update.

Arachidonic acid (AA), a polyunsaturated fatty acid with four double bonds, has multiple actions on living cells. Many of these effects are mediated by an action of AA or its metabolites on ion channels. During the last 10 years, new types of ion channels, transient receptor potential (TRP) channels, store-operated calcium entry (SOCE) channels and non-SOCE channels have been studied.

ONO-54918-07, a stable prostacyclin analogue, mimics the effect of prostaglandin PGE1 on NG108-15 cells.

The aim of this study was to explore the effect of 0NO-54918-07, a stable prostacyclin analogue, on the current-voltage (IV) curve and the intracellular Ca2+ concentration [Ca2+]i of NG108-15 neuroblastoma x glioma hybrid cells. The IV curve was measured with ramp pulses from -70 to 0 mV, and [Ca2+]i was determined with Fura 2. Bath application of 0.

The effect of prostaglandin E1 on ion currents of NG108-15 cells.

The aim of this study was to elucidate the mechanism by which prostaglandin E(1) (PGE(1)) acts on ion currents of whole-cell voltage-clamped NG108-15 neuroblastomaxglioma hybrid cells. Ruptured and perforated patch were used. The holding current at -70 mV, the current-voltage curve produced by ramp pulses from -70 to 0 mV and the T-type and hva (high-voltage-activated) Ca(2+) currents associated with rectangular pulses were recorded.

Prostaglandin El induces an inward current in voltage-clamped NG108-15 cells.

The aim of this study was to explore the effect of prostaglandin E1 (PGE1) on the membrane current of whole-cell voltage-clamped NG108-15 neuroblastoma x glioma hybrid cells. Perforated patch was used. The membrane current at -70 mV (leakage current) and the current-voltage curve produced by ramp pulses from -70 to 0 mV were recorded; from the I-V curve, the conductance of the leakage current and its reversal potential were determined.

A short-chain peptide toxin isolated from Centruroides sculpturatus scorpion venom inhibits ether-à-go-go-related gene K(+) channels.

From the venom of the American scorpion Centruroides sculpturatus Ewing we have isolated a minute peptide fraction (named CsEKerg1) which reversibly inhibits the current through ERG (ether-à-go-go-related gene) K(+) channels. Isolation was done by CM-cellulose column chromatography and reversed phase high-performance liquid chromatography. To test for an effect on ERG channels we used NG108-15 neuroblastomaxglioma hybrid cells voltage-clamped in the whole-cell mode.

Slowing of ERG current deactivation in NG108-15 cells by the histidine-specific reagent diethylpyrocarbonate.

The aim of this study was to explore and characterize the effect of the histidine-specific reagent diethylpyrocarbonate (DEPC) on the ERG (ether-à-go-go related gene) channels of whole-cell voltage-clamped NG108-15 neuroblastoma x glioma hybrid cells. The channels were fully activated by long depolarizing prepulses. Hyperpolarizing pulses elicited K+ inward currents which deactivated after reaching a peak.

Effect of low external calcium on the ERG current of NG108-15 cells.

K(+) currents through ERG (ether-à-go-go related gene) channels were recorded in whole-cell voltage clamped NG108-15 neuroblastomaxglioma hybrid cells. The channels were fully activated by low holding potential (V(H)=-20 mV) and long depolarizing prepulses. Hyperpolarizing pulses elicited inward currents which deactivated after reaching a peak.

Inactivation of the ERG current in NG108-15 cells.

Differentiated NG108-15 neuroblastoma x glioma hybrid cells were whole-cell voltage clamped. The rate of inactivation of ERG (ether-à-go-go related gene) potassium channels was measured with a three-pulse protocol. Contamination with delayed rectifier current at positive potentials was avoided by using the selective ERG channel blocker E-4031.

Separation of M-like current and ERG current in NG108-15 cells.

Differentiated NG108-15 neuroblastoma x glioma hybrid cells were whole-cell voltage-clamped. Hyperpolarizing pulses, superimposed on a depolarized holding potential (-30 or -20 mV), elicited deactivation currents which consisted of two components, distinguishable by fitting with two exponential functions. Linopirdine [DuP 996, 3,3-bis(4-pyridinylmethyl)-1-phenylindolin-2-one), a neurotransmitter-release enhancer known as potent and selective blocker of the M-current of rat sympathetic neurons, in concentrations of 5 or 10 microM selectively inhibited the fast component (IC50 = 14.

The effects of bradykinin on K+ currents in NG108-15 cells treated with U73122, a phospholipase C inhibitor, or neomycin.

1. Bradykinin has multiple effects on differentiated NG108-15 neuroblastoma x glioma cells: it increases Ins(1,4,5)P3 production and intracellular Ca2+ concentration [Ca2+]i evokes a Ca2+ activated K+ current (IK(Ca)) and inhibits M current (IM). We studied the effect of the aminosteroid U73122 and the antibiotic neomycin, both putative blockers of phospholipase C (PLC), on these four bradykinin effects.

Modulation of neuronal calcium channels by arachidonic acid and related substances.

Low-voltage-activated (l-v-a) and high-voltage-activated (h-v-a) Ca2+ currents (ICa) were recorded in whole-cell voltage clamped NG108-15 neuroblastoma x glioma hybrid cells. We studied the effects of arachidonic acid (AA), oleic acid, myristic acid and of the positively charged compounds tetradecyltrimethylammonium (C14TMA) and sphingosine. At pulse potentials > -20 mV, AA (25-100 microM) decreased l-v-a and h-v-a ICa equally.

Model experiments on squid axons and NG108-15 mouse neuroblastoma x rat glioma hybrid cells.

Three types of ionic current essentially determine the firing pattern of nerve cells: the persistent Na+ current, the M current and the low-voltage-activated Ca(2)+ current. The present article summarizes recent experiments concerned with the basic properties of these currents. Keynes and Meves (Proc R Soc Lond B (1993) 253, 61-68) studied the persistent or steady-state Na+ current on dialysed squid axons and measured the probability of channel opening both for the peak and the steady-state Na+ current (PF(peak) and PF(ss)) as a function of voltage.

Bovine serum albumin selectively increases the low-voltage-activated calcium current of NG108-15 neuroblastoma x glioma cells.

The effect of bovine serum albumin (BSA) on the neuronal Ca2+ current (ICa) has been studied in NG108-15 cells. BSA selectively increased the low-voltage-activated (l-v-a), transient ICa but did not affect the high-voltage-activated (h-v-a) ICa. The increase of l-v-a ICa was partly due to a small shift of its activation curve to more negative values of membrane potential and partly to an increase of the maximal activatable current.

Protein kinase C as mediator of arachidonic acid-induced decrease of neuronal M current.

The M current, IM, of NG108-15 neuroblastoma x glioma hybrid cells, a non-inactivating K+ current, is decreased by arachidonic acid (5-25 microM), often after an initial transitory increase. To test the possibility that the decrease is caused by activation of protein kinase C (PKC) we used the PKC 19-31 peptide, which is an effective inhibitor of PKC. With 1 microM peptide in the pipette solution the normally observed strong reduction of IM by 1 microM phorbol 12,13-dibutyrate (PDB) was almost totally prevented, indicating that PKC is completely inhibited; also the voltage dependence of the M conductance, gM(V), was shifted to more negative membrane potentials.

Properties of the voltage sensor for the opening and closing of the sodium channels in the squid giant axon.

A combination of data from standard I-V curves, and from steps applied either at the initial current peak or in the inactivated steady state, yielded values of the total probability of the two open states of the sodium channel, multiplied by a constant scaling factor, as a function of membrane potential. The probability function PFpeak was found to reach a maximum for pulses to 40-50 mV, but for larger test potentials it underwent a slight decline. The curve for its rise was shifted in a positive direction by several millivolts when the temperature was raised.

The effect of arachidonic acid on the M current of NG108-15 neuroblastoma x glioma hybrid cells.

The M current, IM, a voltage-dependent non-inactivating K+ current, was recorded in NG108-15 neuroblastoma x glioma hybrid cells, using the whole-cell mode of the patch-clamp technique. We studied the effect of arachidonic acid, other fatty acids and inhibitors of the arachidonic acid metabolism. In relatively high concentrations (25-50 microM) arachidonic acid first increased and later decreased the current, Ih, which holds the membrane potential at -30 mV and mainly flows through open M channels.

The dual effect of internal tetramethylammonium ions on the open states of the sodium channel in the squid giant axon.

Voltage-clamp recordings of INa in squid axons dialysed with Cs or TMA, and bathed in low Na choline seawater, showed that, except close to threshold, the initial peak of fast-inactivating current was invariably decreased by TMA, whereas the non-inactivating current in the steady state was simultaneously increased. The results suggest that although TMA does not act directly on the movements of the voltage sensors that activate the sodium system, it blocks single-channel conductance in a voltage-dependent fashion in both the open states of the Na channel, while it has an entirely different type of action by increasing the probability of late openings in the steady state. Another difference between the two open states was that the sodium permeability coefficient had a Q10 of 1.

The effect of phloretin on single potassium channels in myelinated nerve.

The effect of phloretin, a dipolar organic compound, on single potassium channel currents of myelinated nerve fibres of Xenopus laevis has been investigated, using inside-out patches prepared by the method of Jonas et al. (1989). The I channel, a potential dependent K channel with intermediate deactivation kinetics, was reversibly blocked by 20 microM phloretin applied on the inside; the block was strongest at negative membrane potentials and less pronounced at positive potentials.

Inhibition of the M current in NG 108-15 neuroblastoma x glioma hybrid cells.

The M current, IM, a voltage-dependent non-inactivating K current, was recorded in NG108-15 neuroblastoma x glioma hybrid cells, using the whole-cell mode of the patch-clamp technique. We studied inhibition of the M current by bradykinin, phorbol dibutyrate (PDBu), an activator of protein kinase C (PKC), and methylxanthines. Focal application of 0.

Phloretin affects the fast potassium channels in frog nerve fibres.

The effect of phloretin (20-100 microM), a dipolar organic compound, on the voltage clamp currents of the frog node of Ranvier has been investigated. The Na currents are simply reduced in size but not otherwise affected. Phloretin has no effect on the slow 4-aminopyridine-resistant K channels.

A slow component in the gating current of the frog node of Ranvier.

The slow component of the gating current on-response has been studied on voltage-clamped nodes of Ranvier of the frog Rana esculenta. At 0 mV and 20 degrees C the charge and the time constant of the slow component were on average 37.1 fC and 0.