Biomedical subjects

D Büsselberg

Publications and source records attributed to D Büsselberg.

At least 37 records · Page 2Linked to original sources

PubMed1994

Aluminium reduces glutamate-activated currents of rat hippocampal neurones.

The actions of aluminum on glutamate-activated currents of acutely isolated hippocampal neurones were investigated. N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) and glutamate mediated currents were reduced by 50% in the presence of 1.4 micrograms ml-1 aluminium. Higher concentrations (> or = 2.7 micrograms ml-1) inhibited all currents completely and irreversibly. Additionally, successive application of agonists in the presence of 2.7 micrograms ml-1 aluminium resulted in non-specific membrane currents followed by the loss of the seal resistance. Application of aluminium per se had no influence on resting membrane current or voltage-activated sodium currents. The estimation of the concentration-response relationship of the action of aluminium on NMDA-activated currents revealed a threshold concentration < 0.27 micrograms ml-1. Our data indicate that glutamate receptors are putative sites of action in aluminium neurotoxicity.

Aluminum↗

PubMed1994

Mercury (Hg2+) and zinc (Zn2+): two divalent cations with different actions on voltage-activated calcium channel currents.

1. We examined the actions of mercury (Hg2+) and zinc (Zn2+) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique. 2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of -80 to 0 mV (mainly L- and N-currents) were reduced by Hg2+ and Zn2+. The threshold concentration for Hg2+ effects was 0.1 microM and that for Zn2+ was 10 microM. Voltage-activated calcium channel currents were abolished (> 80%) with 5 microM Hg2+ or 200 microM Zn2+. The peak calcium current was reduced to 50% (IC50) by 1.1 microM Hg2+ or 69 microM Zn2+. While Zn2+ was much more effective in reducing the T-type calcium channel current--activated by jumping from -80 to -35 mV--Hg2+ showed some increased effectiveness in reducing this current. 3. The effects of both cations occurred rapidly and a steady state was reached within 1-3 min. While the action of Zn2+ was not dependent on an open channel state, Hg2+ effects depended partially on channel activation. 4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg2+ and with higher concentrations (> 100 microM) of Zn2+. 5. As Zn2+ in the concentration range used had no influence on resting membrane currents, Hg2+ caused a clear inward current at concentrations > or 2 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Pb2+ reduces voltage- and N-methyl-D-aspartate (NMDA)-activated calcium channel currents.

1. While intracellular calcium concentrations are closely regulated, two types of ion channels in neurons allow calcium influx: both voltage-activated and NMDA-activated channels are significantly permeable to calcium. In this study we compare the effects of lead (Pb2+) on currents carried through voltage-activated calcium channels and NMDA-activated channels. 2. Pb2+ reduces voltage-activated calcium channel currents elicited by a voltage jump from -80 to 0 mV at 0.1 to 1 microM, with an IC50 of 0.64 microM and a Hill slope of 1.22. This effect was partially reversible and not voltage dependent. Sodium and potassium currents were relatively unaffected at Pb2+ concentrations sufficient to block calcium channel currents by more than 80%. Pb2+ is, thus, a potent, reversible and selective blocker of voltage-dependent calcium channel currents. 3. A fast reversible and slow irreversible blocking action of Pb2+ was found on NMDA-activated currents. When Pb2+ was applied simultaneously with aspartate and glycine (Asp/Gly), the inward currents were rapidly and reversibly reduced in a dose-dependent manner with a minimum effective concentration below 2 microM and a total blockade (> 80%) with 100 microM Pb2+. The IC50 was approximately 45 microM and the Hill coefficient 1.1. Preincubation with 50 microM Pb2+ resulted in a greater reduction in the response to Asp/Gly/Pb2+. This effect was reversed within 2 to 5 sec of wash. The lack of voltage dependence suggests that Pb2+ does not block the channel but rather alters the binding of agonists. Prolonged superfusion of a cell with the Asp/Gly/Pb(2+)-containing external solution resulted in a slow and irreversible decrease in the Asp/Gly activated current.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Actions of aluminum on voltage-activated calcium channel currents.

1. Extracellular and intracellular effects of aluminum (Al) on voltage-activated calcium channel currents (VACCCs) of cultured rat dorsal root ganglion (DRG) neurons were investigated. Al (0.54 to 5.4 micrograms/ml = 20-200 microM) applied extracellularly reduces VACCCs in a concentration-dependent manner. The IC50 was calculated to be 2.3 micrograms/ml (83 microM). All types of VACCCs were similarly reduced by Al treatment. A slight shift of the current-voltage relation to depolarized potentials was observed for higher Al concentrations (> 2 micrograms/ml). The action of Al was found to be use dependent, with little recovery (max. 20%) after wash. 2. The effect of Al was highly pH dependent in the investigated range (pH 6.4 to 7.8). We observed a rightward shift of the concentration-response curve at pH 7.7 (IC50:3.1 micrograms/ml) and a leftward shift at pH 6.4 (IC50:0.56 microgram/ml) compared to the concentration-response curve at pH 7.3. 3. The VACCC declined when 2.7 micrograms/ml Al was added to the internal solution. A steady state was reached within a few minutes. Additional extracellular application of the same concentration lead to an additional decrease of the current. These observations strongly suggest the existence of both intracellular and extracellular accessible binding sites for Al on voltage-activated calcium channels (VACCs). 4. The special characteristics of the action of Al on VACCCs, i.e., the irreversibility, use dependence, and pH dependence, as well as the additional internal binding site may contribute to its neurotoxicity.

Aluminum↗

PubMed1994

Combined actions of Pb2+, Zn2+, and Al3+ on voltage-activated calcium channel currents.

1. Whole-cell patch clamp experiments were performed on rat dorsal root ganglion (DRG) neurons to investigate the actions of various combinations of Pb2+, Zn2+, and Al3+ on voltage-activated calcium channel currents (VACCCs). 2. Each of these metals has been shown to reduce VACCCs. 3. We investigated the effects of simultaneous application of two cations in the range of their IC50 values. For all possible combinations (Pb2+/Zn2+, Zn2+/Al3+, Al3+/Pb2+), independent of the order of application, we found additive actions on VACCCs. 4. We observed a 75% (+/- 9%) block of the control current when two cations were applied simultaneously. This observation is consistent with both, an action of two metals at the same site as well as independent actions at different locations of the ion channel. 5. The additivity of the effects should be taken into account for questions of public health and the assessment of threshold limits in cases of environmental contamination.

Aluminum↗

PubMed1994

Mammalian voltage-activated calcium channel currents are blocked by Pb2+, Zn2+, and Al3+.

1. The effects of the di- and trivalent trace metal cations, Pb2+, Zn2+, and Al3+, on voltage-activated calcium channel currents recorded from cultured rat dorsal root ganglion neurons were determined. 2. All three cations blocked transient and sustained components of the voltage-gated calcium channel currents elicited by a voltage jump from -80 mV to 0 mV, but the trace metals differed in threshold, reversibility, and specificity, and in actions on the different components. 3. Pb2+ was most effective in reducing the voltage-activated calcium channel currents. Threshold concentration for Pb2+ was < 0.1 microM. The threshold for Zn2+ action was < 5 microM and that for Al3+ was approximately 20 microM. Total blockade (> 80%) was obtained with concentrations > 1 microM Pb2+, and 150-200 microM Zn2+ or Al3+. Half of the current was blocked with 0.6 microM Pb2+, 69 microM Zn2+, and 84 microM Al3+. The Hill slope for Pb2+ and Zn2+ action was approximately 1, whereas for Al3+ it was close to 3. 4. Al3+ blockade was clearly use dependent, whereas this was not the case for either Pb2+ or Zn2+. 5. The blockade by none of these metals was totally reversible. The best recovery was obtained upon wash after exposure to Pb2+ (> or = 60%), some recovery was seen with Zn2+ (> or = 50%), but there was little or no recovery after application of Al3+. 6. With Zn2+ or Al3+ in the external solution the current-voltage relation often shifted to depolarized voltages.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗

PubMed1993

Mercury (Hg2+) decreases voltage-gated calcium channel currents in rat DRG and Aplysia neurons.

Inorganic mercury (Hg2+) reduced voltage-gated calcium channel currents irreversibly in two different preparations. In cultured rat dorsal root ganglion (DRG) neurons, studied with the whole cell patch clamp technique, a rapid concentration-dependent decrease in the L/N-type currents to a steady state was observed with an IC50 of 1.1 microM and a Hill coefficient of 1.3. T-currents were blocked with Hg2+ in the same concentration range (0.5-2 microM). With increasing Hg2+ concentrations a slow membrane current was additionally activated, most obviously at concentrations over 2 microM Hg2+. This current was irreversible and might be due to the opening of other (non-specific) ion channels by Hg2+. The current-voltage (I-V) relation of DRG neurons shifted to more positive values, suggesting a binding of Hg2+ to the channel protein and/or modifying its gating properties. In neurons of the abdominal ganglion of Aplysia californica, studied with the two electrode voltage clamp technique, a continuous decrease of calcium channel currents was seen even with the lowest used concentration of Hg2+ (5 microM). A steady state was not reached and the effect was irreversible without any change on resting membrane currents, even with high concentrations (up to 50 microM). No shift of the I-V relation of the calcium channel currents was observed. Effects on voltage-activated calcium channel currents with Hg2+ concentrations such low have not been reported before. We conclude that neurotoxic effects of inorganic mercury could be partially due to the irreversible blockade of voltage-activated calcium channels.

Animals↗

PubMed1993

Voltage gated calcium channel currents of rat dorsal root ganglion (DRG) cells are blocked by Al3+.

The effects of the trivalent cation aluminum (Al3+) on voltage activated calcium channel currents were examined. Al3+ blocks sustained and transient components of voltage activated calcium channel currents of cultured rat dorsal root ganglion (DRG) cells. Currents were elicited by voltage jumps from -80 to 0 mV. The channel block was use dependent. Steady state blockade occurred after 1 to 5 min, when opening the channel every 10 s. There was little or no recovery after washing. Threshold concentration was about 20 microM Al3+ and total blockade (> 80%) was obtained at 200 microM Al3+; the IC50 was 83 microM and the Hill number was around 3. The degree of blockade was pH dependent, and increased with H+ concentration. The current-voltage relation frequently shifted to depolarised voltages after applying Al3+. The degree of the shift was a function of Al3+ concentration, but the magnitude differed from cell to cell. In the effective concentration range (< 200 microM Al3+) the effect was quite specific to voltage activated calcium channel currents. Voltage activated potassium and sodium channels were reduced less than 15% by 200 microM Al3+. We conclude that Al3+ is a potent and irreversible blocker of voltage activated calcium channel currents in mammalian neurons.

Aluminum↗

PubMed1993

Extracellular pH modulates aluminium-blockade of mammalian voltage-activated calcium channel currents.

The pH-dependence of aluminium (Al) blockade of voltage activated calcium channels (VACCs) was investigated. Using cultures of rat dorsal root ganglion (DRG) neurones, whole-cell patch-clamp experiments were performed. Various concentrations of Al were extracellularly applied within solutions of different pH-values. The block of VACC currents was highly pH-dependent. At pH 7.3-7.8, the concentration-response curve shifted slightly to higher concentrations, whereas at pH 6.4-6.9 a pronounced shift to lower concentrations was observed. This effect could be due to changes of the chemical equilibria of the different Al species or to altered properties of the VACCs. Thus, pH-shifts may influence the interactions of Al with VACCs making them more susceptible to the effects of Al and therefore contribute to its toxicity.

Aluminum↗

PubMed1993

Lead blocks LTP by an action not at NMDA receptors.

Exposure of children to low levels of lead results in a reduction in cognitive ability and a series of behavioral deficits. We have studied the effects of PbCl2 on long-term potentiation (LTP), the best available electrophysiologic model of learning and memory, in a rat piriform cortex brain slice preparation in order to test the hypothesis that lead neurotoxicity is a result of actions on LTP. With changes in the composition of the Krebs-Ringer solution normally used in brain slices, it is possible to keep the Pb2+ in solution at concentrations up to 10 microM. In this concentration range, Pb2+ has no effect on the synaptic response elicited in piriform cortex pyramidal neurons upon stimulation of the lateral olfactory tract. We find that Pb2+ blocks LTP by about 75% at 5 microM and completely at 10 microM. At these concentrations, Pb2+ has no effect on posttetanic potentiation. Since it has been reported that Pb2+ blocks N-methyl-D-aspartate (NMDA) responses, and NMDA blockade is known at many sites to block LTP, we studied the effects of Pb2+ on NMDA responses. In the concentration range studied there was no effect of Pb2+ on NMDA responses. The mechanism whereby Pb2+ blocks LTP remains to be determined. While the concentration of Pb2+ found to block LTP in these studies is high relative to concentrations of Pb2+ in blood that are associated with causing cognitive and behavioral effects in children, the sensitivity to Pb2+ may be greater in young animals.

Animals↗

PubMed1993

Pb2+ modulates the NMDA-receptor-channel complex.

The actions of Pb2+ on NMDA channel currents of acutely dissociated hippocampal CA1- and CA3-neurones from adult rats activated by aspartate plus glycine (asp/gly) were examined. A fast reversible and a slow irreversible response to Pb2+ were found. Pb2+ applied simultaneously with asp/gly decreased an inward current. The threshold concentration was below 2 microM, the current was reduced > 90% at concentrations over 100 microM. The decrease of the asp/gly activated current showed no voltage dependence. Opening of NMDA channels was not necessary for Pb(2+)-action, as preincubation in 50 microM Pb(2+)-containing external solution for several seconds dramatically reduced the response to asp/gly/Pb2+. This effect was reversed within 2 to 5 s of wash. Presence of Pb2+ or asp/Pb2+ or glycine/Pb2+ in the external solution did not prevent recovery of the NMDA receptor/channel complex from desensitization. Prolonged perfusion of a cell with the asp/gly/Pb(2+)-containing external solution resulted in an irreversible decrease of the asp/gly current, whereas the amplitude of the asp/gly/Pb2+ response did not change over the duration of an experiment. We conclude that Pb2+ modulates NMDA channel activity via interaction with the NMDA/glycine receptor: as a result the channel current decreases.

Animals↗

PubMed1992

Zinc (Zn2+) blocks voltage gated calcium channels in cultured rat dorsal root ganglion cells.

Dorsal root ganglion cells (DRGs) exhibit 3 types of voltage-dependent calcium channels. We have cultured DRGs from 2- to 4-day-old rat pups and obtained whole-cell patch-clamp recordings of calcium-channel currents after 1-5 days in culture. The calcium-channel currents (carried by barium) were recorded with tetrodotoxin (TTX) in the external solution. A cesium-based solution containing Na-ATP, HEPES and EGTA was used in the recording pipette. Cells were held at -80 mV and calcium channel currents were evoked by stepping to depolarized voltages. The divalent cation zinc (Zn2+) blocked sustained and transient voltage sensitive calcium channel currents. Onset of the blockade was fast and a steady-state was reached within 5-15 min, depending upon the concentration used. The IC50 for inhibition of the peak current evoked by a step depolarization from -80 mV to 0 mV (N plus L channels) for 80 ms was 69 microM Zn2+ and the Hill slope about 1. The calcium current evoked by a voltage step from -80 mV to voltages between -40 mV and -15 mV (T-type current) was more sensitive (> 80% block with 20 microM Zn2+). During wash the effect was only partly reversible in 50% of the neurons. Thus, Zn2+ is a potent blocker of voltage dependent calcium currents in mammalian neurons, especially of T-type currents.

Animals↗

PubMed1991

Pb2+ blocks calcium currents of cultured dorsal root ganglion cells.

The divalent cation lead (Pb2+) blocks sustained and transient voltage sensitive calcium channel currents of cultured rat dorsal root ganglion cells. The IC50 for inhibition of the total peak current evoked by a step depolarization from -80 to 0 mV was 0.6 microM, compared to an IC50 of 2.2 microM for Cd2+. The current activated by a depolarization from -40 to 0 mV was inhibited by 50% by 1.0 microM Pb2+. Low threshold currents activated by a step from -100 to -30 mV were blocked by Pb2+ at higher concentrations (IC50 = 6 microM). The block progressed in the absence of channel activation and showed little voltage dependence. Peak sodium current was reduced by 6.6% at 1 microM Pb2+ while at 20 microM the peak current was reduced by 40% with marked slowing of the time course of activation. The potassium rectifier current was reduced by 4.1% at 1 microM Pb2+. Thus, Pb2+ selectively blocks calcium currents at concentrations in the range of those causing toxicity in man.

Animals↗

PubMed1991

Properties of tuberomammillary histamine neurones and their response to galanin.

Histaminergic neurones in the tuberomammillary nucleus possess electrophysiological properties which distinguish them from other neurones in their neighborhood. Their resting potential is -50 mV and they are spontaneously active at about 2 Hz in a slice preparation. They display a transient outward rectification and an anomalous inward rectification. Bath application of galanin (0.1 microM) reduced their firing rate significantly and hyperpolarized them slightly.

Action Potentials↗

PubMed1991

Lead and zinc block a voltage-activated calcium channel of Aplysia neurons.

1. The effects of Pb2+ and Zn2+ on the peak of the voltage-activated calcium current of Aplysia neurons were examined. Calcium currents were reversibly blocked by Pb2+ at concentrations that did not significantly affect potassium and sodium currents and by Zn2+ at concentrations associated with a delay and reduction of peak sodium and potassium currents. 2. The block by both was concentration dependent, and percentage blockade was reduced in elevated Ca2+. The threshold Pb2+ concentration for blockade in 20 mM Ca artificial sea water (ASW) was approximately 1 microM, whereas for Zn2+ it was 2 mM. The Hill coefficient for Pb2+ action was near 1.0 under all conditions, whereas for Zn2+ it was 1.4-1.6. 3. With addition of Pb2+, the voltage at which peak calcium current was generated shifted to hyperpolarized voltages, an effect similar to that caused by reduction of Ca2+ concentration in the absence of Pb2+. Zn2+ shifted the voltage at which peak current was generated in a depolarizing direction. 4. Pb2+ did not significantly change inactivation but shifted the voltage dependence of activation to hyperpolarized voltages in a dose-dependent manner. Zn2+ shifted both activation and inactivation in a depolarizing direction in a dose-dependent fashion. 5. The blockade of calcium currents by Pb2+ but not Zn2+ was highly voltage dependent and increased with depolarization. 6. Our results suggest that Pb2+ is a specific, potent, competitive, and reversible blocker of calcium currents. These observations are consistent with a competition by Pb2+ with Ca2+ at a binding site within the calcium channel. In contrast, the blockade of calcium currents by Zn2+ is probably through actions at fixed charge sites external to the channel.

Animals↗

PubMed1991

Effects of inorganic and triethyl lead and inorganic mercury on the voltage activated calcium channel of Aplysia neurons.

Using conventional two electrode voltage clamp techniques we have studied the effects of Pb2+, triethyl lead (TEL) and Hg2+ on voltage-activated calcium channels of Aplysia neurons and found that all three metals are potent inhibitors at micromolar concentrations. However, the time course of current reduction or block and its reversibility vary when comparing Pb2+ to TEL and Hg2+. With application of Pb2+ the calcium current decreases immediately and a steady state is reached within three to seven minutes, depending upon the concentration of Pb2+ (IC50 = 61 microM). The block was easily reversed upon wash out of Pb2+ with a time course similar to that of onset. Perfusion with either TEL (5 to 50 microM) or Hg2+ (5 to 200 microM) resulted only in a small reduction of current when the substances reached the cell membrane but with clear reduction within 2 min. The decrease continued at about the same speed for the total duration of the application. Upon washing there was no recovery of the response. At the onset of washing the rate of current decline stopped for several minutes, but then the current continued to decline at a slower rate in the absence of toxicant. Our data suggest that Pb2+ acts by a direct and reversible blockade of the calcium channel. In contrast TEL and Hg2+ act slowly and irreversibly to block calcium channels at concentrations which do not greatly affect membrane potential or resistance. In spite of the slow time course these substances are probably acting directly on the calcium channel.

Animals↗

PubMed1990

Zn2+ blocks the voltage activated calcium current of Aplysia neurons.

We have investigated the effect of Zn2+ on voltage-activated calcium currents of Aplysia neurons, using conventional two-electrode voltage-clamp techniques. The peak of these currents was reversibly reduced by Zn2+ (50% reduction at 3.75 mM; total block at 20 mM), while the current-voltage relation and the activation and inactivation curves were shifted to depolarized voltages. The effects of Zn2+ were concentration-dependent. The Hill coefficient was 1.62. The high concentrations required, the shift of the current-voltage relation and the effects on activation and inactivation are best explained by a charge-screening effect combined with a specific binding site for Zn2+ near the entrance of the channel.

Animals↗

PubMed1990

Lead inhibits the voltage-activated calcium current of Aplysia neurons.

Lead is a potent and reversible inhibitor of the voltage-dependent calcium current of Aplysia neurons in a concentration range (1-1000 microM) similar to that which elicits toxic effects in man. The threshold for inhibition is 1 microM and the dissociation constant about 90 microM. The inhibition is due to reduction of the peak current amplitude, and not due to alteration of the voltage dependence of the activation or inactivation. The effect of lead is specific to the calcium current as the delayed rectifier potassium and the sodium currents are not affected by concentrations of lead (200 microM) which give near-maximal inhibition. The calcium current of Aplysia neurons appears similar to the current flowing through the mammalian L-type calcium channel. This suggests that inhibition of the investigated calcium channel may contribute to the toxic effects of lead in mammals.

Animals↗