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A Mathie

Publications and source records attributed to A Mathie.

33 records · Page 2Linked to original sources
PubMed1993

Block of potassium currents in rat isolated sympathetic neurones by tricyclic antidepressants and structurally related compounds.

1. The block of K+ currents by the tricyclic antidepressants (TCAs), imipramine and amitriptyline and three structurally related compounds, chlorpromazine, tacrine and carbamazepine was investigated in rat isolated sympathetic neurones by whole-cell voltage-clamp recording. 2. At a concentration of 10 microM, imipramine, amitriptyline and chlorpromazine all blocked the delayed rectifier K+ current (IKv) by about the same extent, 54%, 47% and 53%. Tacrine was less effective (10%) while carbamazepine was ineffective at all concentrations tested. 3. The degree of block by the four effective compounds was relatively independent of the size of the voltage-step. Neither the activation nor the inactivation rates of IKv were altered by the blocking drugs. 4. Concentration-response relationships for imipramine and tacrine showed that imipramine was about 7 fold more potent than tacrine but that the maximum inhibition and the Hill slope were the same for both compounds. 5. Amitriptyline, chlorpromazine and imipramine (at 10 microM) were 2-3 fold more potent at inhibiting the sustained K+ current (mostly IKv) than the transient K+ current (mostly IA). Tacrine, however, was equally effective in blocking both components.

Amitriptyline↗
PubMed1992

Characterization of muscarinic receptor subtypes inhibiting Ca2+ current and M current in rat sympathetic neurons.

Muscarinic receptors mediating suppression of Ca2+ current and of M-type K+ current in rat superior cervical ganglion neurons were subclassified pharmacologically by using the muscarinic receptor antagonists pirenzepine and himbacine. Our voltage clamp experiments previously distinguished fast and slow intracellular signaling pathways coupling muscarinic receptors to calcium channels. We now establish that the fast, pertussis toxin-sensitive suppression of Ca2+ current is mediated primarily by muscarinic receptors of the M4 subtype, whereas the slow, bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetate (BAPTA)-sensitive suppression of Ca2+ current is mediated primarily by muscarinic receptors of the M1 subtype. Both actions on Ca2+ current are blocked by guanosine 5'-[beta-thio]diphosphate. Muscarinic suppression of M current is slow, BAPTA-sensitive, and mediated by receptors of the M1 subtype. Hence the two muscarinic pathways use different receptors and different guanine nucleotide binding proteins to produce different actions on channels.

Animals↗
PubMed1992

Inhibition of N- and L-type calcium channels by muscarinic receptor activation in rat sympathetic neurons.

Modulation of N- and L-type Ca2+ channels by oxotremorine-M (oxo-M) acting on muscarinic receptors and norepinephrine (NE) acting on alpha-adrenergic receptors was studied in superior cervical ganglion neurons. Oxo-M depresses dihydropyridine-augmented tail currents in whole-cell recordings, whereas NE does not. This modulation of L-type Ca2+ channels by oxo-M is abolished by adding 20 mM BAPTA to the pipette solution. Oxo-M, acting via a diffusible messenger, reduces the probability of opening of single N- and L-type channels recorded in cell-attached patches. We conclude that a diffusible messenger signaling pathway activated by oxo-M inhibits both N- and L-type Ca2+ channels, whereas a membrane-delimited pathway activated by oxo-M and NE inhibits only N-type Ca2+ channels.

Animals↗
PubMed1992

5-HT3 receptor channels in dissociated rat superior cervical ganglion neurons.

1. Whole-cell and single-channel voltage-clamp techniques were used to record the 5-HT3 receptor-mediated currents in neurons freshly dissociated from rat superior cervical ganglia. 2. Whole-cell currents elicited by brief pressure ejection of 5-HT (10 microM) reversed at -4.5 mV when extracellular and intracellular solutions mainly contained NaCl and CsCl. The peak current-voltage relation showed modest inward rectification that was fully developed within less than 2 ms of the applied voltage step. 3. With prolonged application of 5-HT (10 microM) using a fast perfusion system, the response desensitized in two phases with fast and slow time constants of 0.57 and 6.0 s at -74 mV. The time constants showed little voltage dependence; however, the relative amplitude of the two components was significantly dependent on voltage. The time course of desensitization was not affected by agents that increase the levels of intracellular cyclic AMP. 4. The relative permeability of the channel was determined from reversal potential changes. The channel passed small cations non-selectively, with permeability ratios (PX/PNa) of 0.93 and 1.24 for Cs+ and K+. The organic cations Tris and glucosamine were measurably permeant with permeability ratios of 0.19 and 0.06. Ca2+ was fairly permeant with a relative permeability of 0.55 in 20 mM solution and of 0.16 when the concentration of CaCl2 was increased to 115 mM. No permeability was detected for Cl-. 5. Fluctuation analysis of the whole-cell current revealed an apparent single-channel current of approximately 0.18 pA at -74 mV. 6. 5-HT-activated single-channel currents were recorded in excised outside-out patches. When 5-HT (10 microM) was delivered by pressure ejection, channel openings appeared rapidly with a delay of 28 ms. The unitary current was about approximately 0.80 pA at -74 mV. The channel activity induced by bath perfusion of 5-HT (0.8 microM) was significantly reduced by 100 nM of the 5-HT3 receptor-specific antagonists 3-tropanyl-3,5-dichlorobenzoate (MDL 72222) or 3-tropanyl-indole-3-carboxylate (ICS 205-930). 7. The single-channel current-voltage relation was non-linear, with moderate inward rectification similar to that of the whole-cell current. The chord conductance of the channel decreased with membrane depolarization from 14.6 pS at -104 mV to only 9.9 pS at -54 mV. Open-time distributions consisted of two components with mean time constants of 0.45 and 2.8 ms at -104 mV. Burst-length distributions were also made up of two components with time constants of 0.45 and 4.6 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1991

Intracellular Ca2+ buffers disrupt muscarinic suppression of Ca2+ current and M current in rat sympathetic neurons.

The role of intracellular Ca2+ concentration ([Ca2+]i) in the muscarinic suppression of Ca2+ current and M-type K+ current has been investigated in isolated rat sympathetic neurons using the whole-cell patch-clamp technique and fura-2 fluorescence measurements. Muscarinic stimulation suppressed currents without raising [Ca2+]i. Nonetheless, intracellular bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA) (11-12 mM), a Ca2+ chelator, reduced Ca2(+)-current suppression from 82 to 15%. For the latter, we explain the BAPTA action by a requirement for a certain minimum [Ca2+]i for continued operation of the pathway coupling muscarinic receptors to M-type K+ channels. The pathway coupling muscarinic receptors to Ca channels also showed some dependence on [Ca2+]i, but there may also be a blocking action of BAPTA that is independent of Ca2+ chelation.

Animals↗
PubMed1991

Activation of glutamate receptors and glutamate uptake in identified macroglial cells in rat cerebellar cultures.

1. Patch-clamp methods have been used to examine the action of excitatory amino acids on three types of glial cell in cultures of rat cerebellum, namely type-1-like astrocytes, type-2 astrocytes and oligodendrocytes. In addition we have examined glutamate sensitivity of the precursor cell (the O-2A progenitor) that gives rise to type-2 astrocytes and oligodendrocytes. 2. Glutamate (30 microM), quisqualate (3-100 microM), (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA, 10-30 microM) and kainate (10-500 microM) were applied to cerebellar type-2 astrocytes examined under whole-cell voltage clamp. Each of these agonists induced inward currents in cells held at negative membrane potentials. The currents reversed direction near 0 mV holding potential. N-Methyl-D-aspartate (NMDA, 30-100 microM) or aspartate (30 microM) in the presence of glycine (1 microM) did not evoke any whole-cell current changes in type-2 astrocytes. 3. The distribution of glutamate receptors in type-2 astrocytes was mapped with single- or double-barrelled ionophoretic pipettes containing quisqualate or kainate. Application of these agonists (current pulses 100 ms, 50-100 nA) to cells held at -60 mV evoked inward currents of 20-120 pA in the cell soma and 10-80 pA in the processes. Responses could also be obtained at the extremities of processes (approximately 60 microns from the soma). 4. Quisqualate or kainate (at 30 microM) applied to O-2A progenitor cells from rat cerebellum or optic nerve induced whole-cell currents (quisqualate 20-30 pA; kainate 20-50 pA, holding potential, Vh = -60 mV) that reversed near 0 mV. In common with type-2 astrocytes, the progenitor cells did not respond to NMDA (30 microM). 5. Type-1-like astrocytes produced large inward currents to glutamate (30 microM). These currents remained inward-going at holding potentials as positive as +80 mV and were not accompanied by any apparent noise increase. This result can be explained by the presence of an electrogenic glutamate uptake carrier. In cells kept up to 4 days in vitro, quisqualate, kainate and NMDA each failed to produce any whole-cell current changes, indicating the absence of receptors in type-1-like astrocytes at this stage in culture. Furthermore the glutamate uptake currents in type-1-like astrocytes were inhibited when external Na+ was replaced by Li+, although Li+ was found to pass through the glutamate channel in type-2 astrocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Conductance and kinetic properties of single nicotinic acetylcholine receptor channels in rat sympathetic neurones.

1. The unitary conductance of nicotinic acetylcholine (ACh) receptor channels in rat sympathetic neurones has been studied. Conductance estimates varied from 26-48 pS with a mean of 36.8 pS in 1 mM-Ca2+. The main conductance level varied from patch to patch and the presence (or absence) of additional conductance levels also varied. 2. The channels showed large open channel noise and experiments with 300 mM-NaCl in the patch pipette substantially increased the open channel noise. The appearance of detectable step-like transitions within this noise strongly suggested the existence of closely spaced discrete levels. 3. Removal of divalent cations from the external solution increased the unitary channel conductance. Altering the main permeant ion in divalent-free solutions gave the following conductance sequence: K+ (93 pS) greater than Cs+ (61 pS) greater than Na+ (51 pS) greater than Li+(23 pS). 4. Replacement of Na+ by Cs+ in the external solution considerably reduced the current evoked by ACh in whole-cell recordings and the channel-opening frequency in outside-out patches. 5. The kinetic properties of channels activated by ACh and 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) were also studied. At low concentrations of ACh and DMPP the gap distributions were complex and best fitted by the sum of four exponential components. Individual activations (bursts) were interrupted by the two shortest closed periods the briefer of which had time constants of 36 microseconds for ACh and 67 microseconds for DMPP. 6. The distribution of burst lengths had two components for each agonist, each component making up about 50% of the total area under the distribution. For ACh, the time constant of the longer component (12.2 ms) was similar to the decay time constant of excitatory postsynaptic potentials (EPSCs) at similar temperature and potential. For DMPP the time constant of the longer component was 17.6 ms. 7. The relative number of brief gaps per long burst was much larger for ACh than for DMPP. Therefore the corrected mean open time for ACh (0.86 ms) was much shorter than that for DMPP (2.3 ms). 8. In terms of receptor mechanism, the values of the channel opening equilibrium constant (beta/alpha) estimated from these numbers (ACh, 23; DMPP, 25) suggest that both agonists are efficaceous. 9. DMPP is a potent blocker of the channel with an equilibrium dissociation constant (KB) of around 50 microM and blockage gaps of around 1 ms duration. ACh also blocks the channel but with a higher KB of around 470 microM.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1990

Rectification of currents activated by nicotinic acetylcholine receptors in rat sympathetic ganglion neurones.

1. The inward rectification of the whole-cell current evoked by acetylcholine (ACh) and other nicotinic agonists in rat sympathetic ganglion neurones has been studied using patch-clamp recording techniques. The selective nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) (20 microM) induced an average peak current of -367 pA at -50 mV but no detectable outward current at +50 mV. Similar observations were made with ACh and carbachol. 2. The current-voltage relation of the whole-cell response induced by DMPP was linear in the negative voltage range; however, there was no detectable outward current in the voltage range 0 to about +70 mV. Above +70 mV an outward current became clearly detectable. Rapid depolarizing jumps in the holding potential failed to reveal any rapidly decaying outward current. 3. The rectification was not alleviated by changing the main permeant cation, by removal of divalent cations from the intracellular or extracellular solutions or by altering the pH buffer in the extracellular solution from HEPES to Tris. 4. Intracellular magnesium ions can block the channel. This effect increases with depolarization, but dissociation outwards (i.e. permeation by Mg2+) appears to relieve the block at more extreme positive potentials. This effect alone, or in combination with the voltage dependence of the burst length, is unlikely to be able to account for the whole-cell rectification in intact cells, much less that seen in cells perfused with Mg2(+)-free intracellular medium. 5. When the reversal potential was shifted to approximately -50 mV (by the use of impermeant cations) nicotinic agonists produced small outward currents in the membrane potential range -20 to +10 mV while shifting it to about +40 mV produced small inward currents in the potential range 0 to +20 mV. The rectification therefore appears to be independent of the direction of current flow and is maximum at a potential positive to 0 mV. 6. At positive potentials the receptors desensitized much less than at negative potentials in the continued presence of agonist. Thus, exposure of the cells to a steady application of 30 microM-ACh produced no detectable response if the cell was at a positive potential, but when the cell was stepped to a negative potential in the continued presence of ACh (at a time when much of the ACh current would be expected to have desensitized), ACh induced a large inward current. The onset of the ACh current had a time constant of 10 ms. It then decayed with a time constant of 790 ms as desensitization developed.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1988

Acetylcholine receptor channels and their block by clonidine in cultured bovine chromaffin cells.

1. Acetylcholine (10-50 microM) applied to bovine chromaffin cells under whole-cell voltage clamp produced an inward current and an increase in the noise level of the current trace. At concentrations greater than or equal to 20 microM the ACh current desensitized with time. Spectral analysis of the ACh-induced increase in current noise showed that it could be fitted by a single Lorentzian component with a time constant, tau noise = 11 +/- 0.9 ms (Vm = -80 mV). 2. Clonidine (2-30 microM) markedly reduced the size of the ACh-induced whole-cell current, and altered the shape of the noise spectrum. In the presence of clonidine, ACh noise spectra were fitted by two Lorentzian components with time constants which varied with clonidine concentration. The single-channel conductance from noise (gamma = 24 pS) was unaltered by clonidine. 3. The reduction in the size of the whole-cell ACh current, produced by clonidine, was not mimicked by adrenaline (at concentrations up to 60 microM). GABA-induced whole-cell currents and spectra of GABA noise were also unchanged suggesting that the effect of clonidine was specific for the ACh receptor channel. 4. When applied intracellularly (from the patch pipette) clonidine had no apparent influence on the whole-cell ACh current. Furthermore, when clonidine was perfused over the cell surface at a concentration sufficient to block the whole-cell ACh response, single ACh channels could still be recorded under the patch-pipette tip (i.e. in cell-attached patches, not exposed to clonidine). 5. Clonidine block showed little voltage dependence; the peak ACh current remained linearly dependent on clamp potential. In addition, the fast and slow time constants derived from ACh noise spectra in the presence of clonidine did not show the sort of dependence on antagonist concentration expected for simple channel block; this suggests that clonidine has a complex blocking action. 6. Single ACh channels recorded in outside-out patches had a conductance of gamma = 39 +/- 0.7 pS, although a subpopulation of smaller and larger events also occurred in some patches. The mean single-channel conductance in outside-out patches was unaltered by clonidine. 7. Under normal conditions the kinetics of single ACh channels were more complex than suggested from noise analysis. Burst length distributions could be described by two exponential components with fast and slow time constants of tau f = 0.69 +/- 0.17 and tau s = 9.51 +/- 0.84 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1987

Single-channel and whole-cell currents evoked by acetylcholine in dissociated sympathetic neurons of the rat.

Single acetylcholine-activated channels have been recorded from neurons dissociated from the sympathetic chain of 17-21 day old rats. The mean single channel conductance is 35 pS in normal medium containing 1 mM calcium, and 51 pS in the absence of calcium. The measured current amplitudes are about five times more variable than at the frog endplate, at least in part because the current, while the channel is open, is much noisier than when it is shut. Single activations of the receptor by acetylcholine (ACh) produce a burst of openings; the distribution of the burst length has two components, the longer of which is of primary importance in synaptic transmission. Whole-cell currents, in response to ACh (up to 30 microM), show strong inward rectification with no outward current being detectable. This phenomenon is similar whether the intracellular ion is sodium or cesium, whether or not divalent cations are present, and whether or not atropine is present. Nevertheless, outward single-channel currents (of normal conductance) are detectable in isolated outside-out patches.

Acetylcholine↗
PubMed1986

Ion channels activated by acetylcholine and gamma-aminobutyric acid in freshly dissociated sympathetic neurones of the rat.

Transmitter-activated channels in freshly isolated neurones from sympathetic ganglia of young rats have been examined using the patch-clamp technique. Acetylcholine (ACh), gamma-aminobutyric acid (GABA) and (in about one third of cells) glycine produced an inward current and an increase in current noise when perfused onto voltage-clamped neurones. The ACh noise was fitted with a single Lorentzian spectrum with a time constant of 13.1 ms at -70 mV. Outside-out membrane patches allowed high-resolution measurements of single ACh- and GABA-activated channels. The ACh-channels had a conductance of 30 pS.

Acetylcholine↗
PubMed1986

Interactions between the effects of yohimbine, clonidine and [Ca]o on the electrical response of the mouse vas deferens.

Excitatory junction potentials (e.j.ps) were recorded from mouse vas deferens and resolved into families of 'discrete events' (d.es) reflecting intermittent release of packets of transmitter from one or a few sites. Within families d.es vary in amplitude between a few preferred values unaffected by any treatments used in these experiments. As [Ca]o is raised from 1.1 to 4.0 mM there is a rise in d.e. amplitude due to an increase in the frequency of large events and a decrease in that of small. At all [Ca]o clonidine reduces d.e. amplitude by increasing failures and small events and decreasing large events. Yohimbine has opposite effects. Both drug effects are concentration-dependent in the range 5 X 10(-9) - 10(-6)M. As [Ca]o is raised from 1.1 to 4.0 mM, and therefore more natural agonist is released, clonidine becomes more effective at altering d.e. amplitude whereas yohimbine becomes less so. With very low frequency stimulation yohimbine elevates e.j.p. amplitude only if [Ca]o is below 1.6 mM. These results are not easily compatible with the notion that yohimbine breaks a 'negative feedback' control of transmitter release.

Action Potentials↗
PubMed1984

Alpha-adrenoceptors and facilitation at a sympathetic neuroeffector junction.

Excitatory junction potentials were recorded from the mouse vas deferens following 5 stimuli at 1Hz and a single stimulus at times from 100 msec to 9 sec later. E.j.ps facilitate and facilitation decayed over a biexponential time course, with time constants of 120 msec and 4.3 sec. Clonidine (10(-8)-10(-7) M) depressed e.j.p. amplitude, and also accelerated both phases of the decay of facilitation. Yohimbine (10(-7) M) and piperoxan (10(-7)-10(-6) M) increased the amplitude of all but the first e.j.p. in a train, and slowed both phases of the decay of facilitation. One way in which prejunctional modulation by alpha-adrenoceptors may occur is therefore by modifying the carry-over of facilitation from one stimulus to the next.

Animals↗
PubMed1984

Facilitation at single release sites of a sympathetic neuroeffector junction in the mouse.

Electrophysiological techniques were used to observe the release of transmitter from one or a few release sites of the sympathetic neuroeffector junction of the mouse vas deferens. Release produces transient accelerations of the depolarizing phase of the excitatory junction potential, known as 'discrete events'. Discrete events associate into families at a constant latency and peak time, but vary in amplitude between a few preferred values. As facilitation develops there is a decrease in the frequency of small members of families and an increase in the frequency of large members, a change in apparent 'quantal content'. A similar change in amplitude distribution occurs when the [Ca]o is raised. The alpha-adrenoceptor antagonist yohimbine increases quantal content when facilitation has developed, but has no significant effect on unfacilitated discrete event amplitude unless the [Ca]o is below 2.0 mM. The alpha-adrenoceptor agonist clonidine reduces facilitated and unfacilitated quantal content under all conditions examined.

Action Potentials↗