Biomedical subjects

E E Nikolsky

Publications and source records attributed to E E Nikolsky.

At least 19 recordsLinked to original sources

PubMed2006

Negative cross-talk between presynaptic adenosine and acetylcholine receptors.

Functional interactions between presynaptic adenosine and acetylcholine (ACh) autoreceptors were studied at the frog neuromuscular junction by recording miniature end-plate potentials (MEPPs) during bath or local application of agonists. The frequency of MEPPs was reduced by adenosine acting on presynaptic adenosine A1 receptors (EC(50) = 1.1 microm) or by carbachol acting on muscarinic M2 receptors (EC(50) = 1.8 microm). However, carbachol did not produce the depressant effect when it was applied after the action of adenosine had reached its maximum. This phenomenon implied that the negative cross-talk (occlusion) had occurred between A1 and M2 receptors. Moreover, the occlusion was receptor-specific as ATP applied in the presence of adenosine continued to depress MEPP frequency. Muscarinic antagonists [atropine or 1-[[2-[(diethylamino)methyl)-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido [2,3-b][1,4]benzodiazepine-6-one) (AFDX-116)] had no effect on the inhibitory action of adenosine and adenosine antagonists [8-(p-sulfophenyl)theophylline (8-SPT) or 1,3-dipropyl-8-cyclopentylxanthine (DPCPX)] had no effect on the action of carbachol. These data suggested that membrane-delimited interactions did not occur between A1 and M2 receptors. Both carbachol and adenosine similarly inhibited quantal release triggered by high potassium, ionomycin or sucrose. These results indicated a convergence of intracellular pathways activated by M2 and A1 receptors to a common presynaptic effector located downstream of Ca(2+) influx. We propose that the negative cross-talk between two major autoreceptors could take place during intense synaptic activity and thereby attenuate the presynaptic inhibitory effects of ACh and adenosine.

Adenosine↗

PubMed2006

Different sensitivity of miniature endplate currents of the rat extensor digitorum longus, soleus and diaphragm muscles to a novel acetylcholinesterase inhibitor C-547.

A novel derivative of 6-methyluracil, C-547, increased the amplitude and prolonged the duration of miniature endplate currents (MEPCs) which is typical for acetylcholinesterase inhibition. In the soleus and extensor digitorum longus significant potentiation was detected at nanomolar concentrations. In contrast, in the diaphragm muscle, the increase in the amplitudes of the MEPCs and the decay time constant appeared only when the concentration of C-547 was elevated to 1 x 10(-7) M. Possible consequences for the exploitation of this drug, which can selectively inhibit AChE in particular synapses, are discussed.

Animals↗

PubMed2005

Calcium dependence of uni-quantal release latencies and quantal content at mouse neuromuscular junction.

Uni-quantal endplate currents (EPC) were recorded at mouse diaphragm neuromuscular synapse by extracellular microelectrode during motor nerve stimulation. The probability of release expressed as quantal content m(o), and variability of synaptic latencies expressed as P90 were estimated in the presence of extracellular calcium ([Ca2+]o) varying between 0.2 and 0.6 mM in the bathing solution. At 0.2 mM ([Ca2+]o), m(o) was low (0.10) and many of long-latency EPCs were present during the late phase of the release (P90 = 2.44 ms). No change in m(o) was found when ([Ca2+]o) was 0.3 mM, but P90 decreased by 39 %. For latency shortening, saturating concentration of ([Ca2+]o) was 0.4 mM, when P90 was 1.49 ms and latencies did not further change at 0.5 and 0.6 mM ([Ca2+]o). In the latter concentrations, however, an increase of m(o) was still observed. It can be concluded that the early phase of the secretion did not significantly change when ([Ca2+]o) was raised and that only the late phase of the release depends on extracellular calcium up to 0.4 mM.

Action Potentials↗

PubMed2005

Spontaneous quantal and non-quantal release of acetylcholine at mouse endplate during onset of hypoxia.

At 20 (0)C, both quantal and non-quantal spontaneous acetylcholine release (expressed as miniature endplate potential frequency [f-MEPPs] and the H-effect, respectively) increased during the first 30 min of hypoxia in solution with normal extracellular calcium ([Ca(2+)](o) = 2.0 mM). The hypoxia-induced tenfold increase of the f-MEPPs was virtually absent in low calcium solution([Ca(2+)](o) = 0.4 mM) whereas there was still a significant increment of non-quantal release. This indicates that each of these two processes of acetylcholine release is influenced by mechanisms with different oxygen sensitivity. The rise of f-MEPPs during the onset of hypoxia apparently requires Ca(2+) entry into the nerve terminal, whereas the non-quantal release can be increased by another factors such as a lower level of ATP.

Acetylcholine↗

PubMed2001

Temperature effect on carbachol-induced depression of spontaneous quantal transmitter release in frog neuromuscular junction.

The effects of carbachol (CCh) on the frequency (f) of the miniature endplate potentials were tested at temperatures between 5 and 30 degrees C. Higher CCh concentrations, 1 x 10(-5) and 5 x 10(-6) M, reduced the f to 60% and the temperature dependence was negligible. However, an inverse temperature dependence was found when low concentrations 3 x 10(-7) and 6 x 10(-7) M were applied. The depression of f was 40-50% in 5-10 degrees C but only 10-20% of the control in the 25 and 30 degrees C. During application of CCh, the new steady of f was reached at temperatures between 5 and 30 degrees C within 17-20 min (Q10 = 1.07). Much greater temperature dependence of recovery was observed during washing out CCh (Q10 = 1.6). The temperature-independence of the steady state effects of CCh, good agreement with Langmuir adsorption-desorption theory and non-steady kinetics indicate that physical rather than receptor-mediated events are responsible for the depression of f.

Animals↗

PubMed2000

Effect of nitric oxide and NO synthase inhibition on nonquantal acetylcholine release in the rat diaphragm.

After anticholinesterase treatment, the postsynaptic muscle membrane is depolarized by about 5 mV due to nonquantal release of acetylcholine (ACh) from the motor nerve terminal. This can be demonstrated by the hyperpolarization produced by the addition of curare (H-effect). The magnitude of the H-effect was decreased significantly to 3 mV when the nitric oxide (NO) donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) were applied to the muscle, or when NO production was elevated by adding L-arginine, but not D-arginine, as a substrate. The H-effect was increased to 8-9 mV by inhibition of NO synthase by L-nitroarginine methylester (L-NAME), or by guanylyl cyclase inhibition by methylene blue and 1H-[1,2,4]oxidiazolo[4,3-a]quinoxalin-1-one (ODQ). ODQ increased the H-effect to 7.3 +/- 0.2 mV and diminished the SNP-induced decrease of the H-effect when applied together with SNP. The effects of NO donors and L-arginine were eliminated by adding reduced haemoglobin, an extracellular NO scavenger. The present results, together with earlier evidence for the presence of NO synthase in muscle fibres, indicate that nonquantal release of ACh is modulated by NO production in the postsynaptic cell.

Acetylcholine↗

PubMed2000

The effect of carbachol and alpha-bungarotoxin on the frequency of miniature endplate potentials at the frog neuromuscular junction.

The effects of an acetylcholine analogue, carbachol (CCh), and a purified irreversible nicotinic antagonist, -bungarotoxin (BTX), on the frequency of the miniature endplate potentials (mEPPs) at the neuromuscular junction of the frog were tested at 20 and 10 C. CCh (5 10-6 m) reduced the frequency of mEPPs to about 60 %; this reduction was not affected by 1 10-7 g ml-1 BTX. BTX also reversibly decreased the mEPP frequency by 40 %, but not in the presence of CCh or in Ringer solution with 0 or 8 mM Ca2+. The present data show that BTX, which inhibits a class of nicotinic ACh receptors, does not block the decrease of mEPP frequency evoked by CCh and can itself suppress the frequency of spontaneous quantal release.

Animals↗

PubMed2000

Cyclic AMP synchronizes evoked quantal release at frog neuromuscular junctions.

At frog neuromuscular junction, noradrenaline (NA) shortens the release period for evoked quantal release acting on a beta1 receptor. To test the hypothesis that this action of NA is mediated by cAMP, we measured the latencies of focally recorded uni-quantal endplate currents (EPCs) after application of dibutyryl-cAMP (db-cAMP) and adenylyl cyclase activator, forskolin. The interval between the time when responses with minimal delay appeared and the point at which 90% of all latencies had occurred (P90 parameter) was shortened in the presence of both 1 x 10(-6) mol/l db-cAMP and 1 x 10(-6) mol/l forskolin by about 30%. The cAMP-induced shortening is equal to that found after application of NA and effects of both drugs are not additive.

Acetylcholine↗

PubMed2000

Participation of electrogenic Na+-K+-ATPase in the membrane potential of earthworm body wall muscles.

The effect of Na+-K+-ATPase inhibitor ouabain on the resting membrane potential (Vm) was studied by glass microelectrodes in isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris and compared with frog sartorius muscle. In earthworm muscle, Vm was -49 mV (inside negative) in a reference external solution with 4 mmol/l K+. The electrogenic participation of Na+-K+-ATPase was absent in solutions with very low concentrations of 0.01 mmol/l K+, higher in 4 and 8 mmol/l K+ (4-5 mV) and maximal (13 mV) in solutions containing 12 mmol/l K+ where Vm was -46 mV in the absence and -33 mV in the presence of 1 x 10(4) M ouabain. The electrogenic participation of Na+-K+-ATPase was much smaller in m. sartorius of the frog Rana temporaria bathed in 8 and 12 mmol/l K+. The results indicate that the Na+-K+-ATPase is an important electrogenic factor in earthworm longitudinal muscle fibres and that its contribution to Vm depends directly on the concentration of K+ in the bathing solution.

Animals↗

PubMed1999

Noradrenaline synchronizes evoked quantal release at frog neuromuscular junctions.

1. Noradrenaline (NA) increases synaptic efficacy at the frog neuromuscular junction. To test the hypothesis that one of the actions of NA is to shorten the period over which evoked quanta are released, we measured the latencies of focally recorded uniquantal endplate currents (EPCs). 2. NA shortened the release period for evoked quantal release. The interval between the time when responses with minimal delay appeared and the point at which 90 % of all latencies had occurred was shortened in the presence of 1 x 10-5 M NA by about 35 % at 20 C and by about 45 % at 8 C. Inhibitor and agonist experiments showed that NA acts on a beta-adrenoreceptor. 3. The better synchronization of release significantly increased the size of reconstructed multi- quantal EPCs. This suggests that NA facilitates synaptic transmission by making the release of quanta more synchronous. 4. The synchronizing action of NA might potentiate neuromuscular transmission during nerve regeneration, transmitter exhaustion and other extreme physiological states where the quantal content is reduced, such as survival in cold and hibernation.

Adrenergic alpha-Agonists↗

PubMed1999

The glutamate and carbachol effects on the early post-denervation depolarization in rat diaphragm are directed towards furosemide-sensitive chloride transport.

The membrane potentials of denervated muscle fibres of the rat diaphragm kept in a tissue culture medium are depolarized by about 8-10 mV (10-12%) within 3 h after denervation. This early post-denervation depolarization (EPD) is substantially reduced (2-3 mV) when muscle strips are bathed with 1 mM L-glutamate (GLU) which is found in motor nerve endings, or with 5 x 10(-8) M carbachol (CCh), which mimics the effect of nonquantally released acetylcholine (ACh). The hyperpolarizing effects of GLU and CCh on EPD are not influenced by ouabain, an active sodium transport inhibitor, but are absent when Cl- transport is augmented by increased osmolarity (500 mosmol/l) produced by addition of sucrose or NaCl. The EPD and the effect of hyperosmolarity are effectively prevented by the Cl- transport inhibitor furosemide (1 x 10(-4) M) or by a chloride-free bathing medium. It is suggested that the post-denervation cessation of nonquantal ACh release, and probably also GLU release, from nerve endings leads to the activation of the furosemide-sensitive Cl- transport in the sarcolemma, which is responsible for the early post-denervation depolarization.

Animals↗

PubMed1999

Non-quantal acetylcholine release is increased after nitric oxide synthase inhibition.

After anticholinesterase treatment, depolarization of the postsynaptic muscle membrane by about 5 mV develops due to non-quantally released acetylcholine from the motor nerve terminal and can be revealed as hyperpolarization by the addition of curare (H-effect). The H-effect increases significantly to 8.7 mV after inhibition of NO-synthase by L-nitroarginine methylester (L-NAME) whilst no changes in the amplitude and frequency of quantal miniature endplate potentials are observed.

Acetylcholine↗

PubMed1998

The effect of glutamate and inhibitors of NMDA receptors on postdenervation decrease of membrane potential in rat diaphragm.

The early postdenervation depolarization of rat diaphragm muscle fibers (8-10 mV within 3 h in vitro) is substantially smaller (3 mV) when muscles are bathed with 1 x 10(-3) M L-glutamate (Glu) or 1 x 10(-3) M N-methyl-D-aspartate (NMDA). The effects of Glu and NMDA are inhibited in a dose-dependent manner by competitive inhibitor 2-amino-5-phosphonovaleric acid (APV) with Ki 6.3 x 10(-4) M, by 2 x 10(-7) M MK-801, which acts as an open channel inhibitor, by 2-3 x 10(-4) Zn2+, which reacts with surface-located sites of the NMDA subtype of the glutamate receptor, and also by glycine-free solutions and 7-Cl-kynurenic acid, which inhibits the glycine binding sites on NMDA receptors. It follows that the effect of glutamate on early post-denervation depolarization is mediated by the NMDA subtype of glutamate receptor with similar pharmacological properties to those found in neurons. The only exception found was the glutamate-like action of 1 x 10(-7) M MK-801, which partially prevented the early postdenervation depolarization when present in the muscle bath during the first 3 h after nerve section.

Animals↗

PubMed1998

Carnosine and other imidazole-containing compounds enhance the postdenervation depolarization of the rat diaphragm fibres.

In the presence of carnosine, anserine, histidine, imidazole and 7-nitro indazole, the early postdenervation depolarization of muscle of about 8 mV was significantly increased by 2.15-4.8 mV. The presence of the imidazole ring in the molecule is apparently necessary for this effect. These compounds also eliminated an NO-mediated protective effect of L-glutamate and carbachol on the depolarization of membrane potential. The presence of imidazole, 7-nitro indazole, carnosine and anserine did not significantly change the effect of an external NO donor, sodium nitroprusside. The structural and functional similarity between imidazole derivatives and the known NO synthase inhibitor, 7-nitro indazole suggests that imidazole, carnosine and anserine might act by inhibiting NO production which is stimulated by glutamate and carbachol.

Animals↗

PubMed1997

Acetylcholine and carbachol prevent muscle depolarization in denervated rat diaphragm.

Muscle fibres of the rat diaphragm kept in a tissue culture medium became depolarized by 8-10 mV within 3 h after denervation. In the presence of carbachol (CB; 5 x 10(-8) M), and acetylcholine (ACh; 5 x 10(-8) M, the post-denervation depolarization was reduced. Both drugs were used in concentrations which mimicked the effect of non-quantal release of ACh. (+)Tubocurarine (TC) and ouabain did not prevent the protective action of CB, indicating that this effect is not mediated through ACh nicotinic receptors or the electrogenic Na+, K+ pump. Addition of Mg2+, verapamil, diltiazem, nifedipine and Cd2+ in concentrations which block Ca2+ entry virtually inhibited the effect of both cholinomimetics. L-Nitroarginine methylester (NAME), an inhibitor of NO synthase, and haemoglobin, an extracellular scavenger of the NO radical, completely eliminated the protective effect of CB on post-denervation depolarization. The retrograde action of NO produced by cholinomimetics on nerve terminals is postulated.

Acetylcholine↗

PubMed1996

Nitroprusside decreases the early post-denervation depolarization of diaphragm muscle fibres of the rat.

The application of sodium nitroprusside, which degrades to nitric oxide (NO) in solution, inhibits early post-denervation depolarization of isolated rat diaphragm fibres. The observation that "old' solutions of sodium nitroprusside (that have been allowed to decompose) are without effect and that haemoglobin, oxadiazolo quinoxalinone (ODQ) and methylene blue can antagonize the inhibition normally produced by sodium nitroprusside suggests that the inhibitory effects of sodium nitroprusside on early post-denervation depolarization are mediated by NO and guanylyl cyclase. This is in accord with our recent observations with NO synthase activation and inhibition in the diaphragm.

Animals↗

PubMed1996

Non-quantal acetylcholine release in the mouse diaphragm after phrenic nerve crush and during recovery.

The progressive decline and recovery of spontaneous quantal acetylcholine (ACh) release (miniature endplate potentials, MEPPs) and the H-effect were measured in the mouse diaphragm after nerve crush and during regeneration. The H-effect is the hyperpolarization of the muscle fibre membrane produced by the addition of (+)tubocurarine, which indicates non-quantal ACh release. One hour after nerve crush the H-effect had declined to 50% of control values and 4 h later the H-effect disappeared completely. There were no substantial changes in the MEPP frequency and amplitude during the first 4 h after denervation. MEPP frequency then increased, but after 6 h of denervation it decreased and after 16 h no MEPPs were found in any of the muscle fibres. The times of onset of these denervation changes in the proximal, central and distal parts of diaphragm were similar. During reinnervation, the H-effect was detectable in all muscle parts 3 days before the reappearance of MEPPs. The H-effect developed first on day 8 in the proximal endplates and then, with a delay of 3 and 6 days, in the central and distal areas, respectively. During axonal regrowth the non-quantal release was restored before detectable quantal release. Non-quantal release is the first indication of the ability of the nerve terminal to release ACh in the process of reinnervation.

Acetylcholine↗

PubMed1995

The role of non-quantal release of acetylcholine in regulation of postsynaptic membrane electrogenesis.

In mammalian nerve-muscle preparations treated with an anticholinesterase, the acetylcholine (ACh) released non-quantally (NQR) reaches the postsynaptic receptors and causes a small depolarization of the membrane potential at the endplate region of the muscle fibres. Increase in quantal release potentiates the NQR and vice versa, the amplitude and the kinetic parameters of quantal miniature endplate currents (MEPCs) change during manipulation of NQR, indicating direct interaction between both types of release. Repetitive binding of ACh to postsynaptic receptors which prolongs the time course of MEPCs in anti-cholinesterase-treated endplates leads within 1-2 h to progressive desensitization in the presence of non-quantal release and to the subsequent shortening of the quantal responses. We have also investigated the effect of procedures known to modulate non-quantal acetylcholine release, on the small, but obvious, difference in the resting membrane potential between the endplate zone and other areas of the mouse muscle fibre. The resting membrane potential at the endplate zone with intact cholinesterase is more negative (by 2-4 mV) than in the endplate-free area. The experiments were performed to test the hypothesis that the hyperpolarization is caused by an electrogenic Na(+)-K+ pump operating during the action of ACh released in non-quantal form. Observations in favour of this idea are that both short-term denervation (which eliminates non-quantal but not quantal release) and ouabain abolish the local synaptic hyperpolarization and that subsequent application of low doses of ACh restores it. It follows, therefore, that the hyperpolarization is probably caused by a small but continuous ACh leakage from the nerve terminal.

Acetylcholine↗