Biomedical subjects

A Surprenant

Publications and source records attributed to A Surprenant.

105 records · Page 6Linked to original sources

PubMed1987

A non-adrenergic, non-cholinergic slow inhibitory post-synaptic potential in neurones of the guinea-pig submucous plexus.

1. Intracellular recordings were made from neurones in the submucous plexus of guinea-pig ileum and caecum. The responses to electrical stimulation of fibre strands entering the nodes of the plexus were studied. 2. Stimuli comprising trains of pulses (20 Hz, 1-5 s) produced nicotinic excitatory post-synaptic potentials (fast e.p.s.p.s), an adrenergic inhibitory post-synaptic potential (i.p.s.p.), a slow excitatory post-synaptic potential (slow e.p.s.p.) and a fourth, hitherto unnoticed, slow hyperpolarization which followed the slow e.p.s.p. All these responses were abolished by tetrodotoxin or solutions containing a low calcium concentration. 3. The slow hyperpolarization (slow i.p.s.p.) was examined in the presence of blockers of the nicotinic and adrenergic responses, and in conditions in which the slow e.p.s.p. was prevented by desensitizing concentrations of substance P or vasoactive intestinal polypeptide. The slow i.p.s.p. was unaffected by prazosin (0.1-1 microM), propranolol (0.1-1 microM), atropine (1 microM) or naloxone (1 microM). 4. The amplitude and duration of the slow i.p.s.p. increased with increasing numbers of stimulus pulses; it had an amplitude of 17 mV and a duration of 70 s when evoked by a stimulus of 20 Hz for 3 s. 5. The slow i.p.s.p. was associated with a decrease in the input resistance of the cell. It reversed polarity at -90 mV in 4.7 mM-potassium and the extrapolated reversal potential in 0.47 mM-potassium was -145 mV; these findings indicate that the slow i.p.s.p. results from an increase in membrane potassium conductance. 6. The slow i.p.s.p. could still be recorded from submucous plexus neurones in segments of ileum which had been extrinsically denervated 6-11 days previously.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1985

mu-Opioid receptors and alpha 2-adrenoceptors coexist on myenteric but not on submucous neurones.

Intracellular recordings were made from neurones in the myenteric and submucous plexuses of the guinea-pig ileum. All myenteric neurones that were hyperpolarized by [Met5]enkephalin (or normorphine) were also hyperpolarized by noradrenaline (or clonidine); neurones unaffected by opioids were unaffected by noradrenaline. The hyperpolarizations resulted from an increase in potassium conductance of the membrane and were blocked by the respective antagonists naloxone and idazoxan. Neurones of the submucous plexus were hyperpolarized by noradrenaline but not by normorphine. The results suggest that myenteric neurones possesses both mu-opioid receptors and alpha 2-adrenoceptors whereas submucous neurones have alpha 2-adrenoceptors but not mu-opioid receptors.

Animals↗

PubMed1985

Inhibitory synaptic potentials resulting from alpha 2-adrenoceptor activation in guinea-pig submucous plexus neurones.

Intracellular recordings were obtained from neurones of the guinea-pig submucous plexus. Inhibitory synaptic potentials (i.p.s.p.s) were compared with hyperpolarizations evoked by brief, local applications of noradrenaline and by superfusion with adrenoceptor agonists. Hyperpolarizing potentials elicited by brief applications of noradrenaline were similar to the i.p.s.p. in latency of onset, amplitude, time course, conductance increase, reversal potential and ionic dependence. Both responses were blocked by low concentrations of Ba2+ and quinine. 6-hydroxydopamine selectively and irreversibly abolished the i.p.s.p. and resulted in a complete loss of catecholamine fluorescent nerve fibres in the submucous plexus. The alpha 2-adrenoceptor antagonists, phentolamine, yohimbine and RX781094, reversibly blocked the i.p.s.p. and the noradrenaline hyperpolarization. Prazosin, propranolol, atropine and naloxone had no effect on these responses. Superfusion with noradrenaline and clonidine produced dose-dependent membrane hyperpolarizations. Noradrenaline and clonidine dose-hyperpolarization curves were shifted to the right in a parallel fashion by alpha 2-adrenoceptor antagonists. Determination of the dissociation equilibrium constants for phentolamine, yohimbine and RX781094 showed that the hyperpolarization produced by noradrenaline perfusion is due to alpha 2-adrenoceptor activation. It is concluded that the release of noradrenaline from sympathetic nerves activates post-synaptic alpha 2-adrenoceptors, resulting in the K+ conductance increase which underlies the i.p.s.p. in submucous plexus neurones.

Action Potentials↗

PubMed1985

Muscarinic M1 and M2 receptors mediate depolarization and presynaptic inhibition in guinea-pig enteric nervous system.

Intracellular recordings were made from guinea-pig myenteric and submucous plexus neurones. Nicotinic excitatory post-synaptic potentials (fast e.p.s.p.s) and slow e.p.s.p.s were recorded in both plexuses; adrenergic inhibitory post-synaptic potentials (i.p.s.p.s) were recorded from submucous plexus neurones. The effects of muscarinic agonists and antagonists were examined on the synaptic potentials in those neurones in which these substances did not change the membrane potential. Muscarine, oxotremorine, methylfurmethide and McNeil A343 reversibly depressed the amplitude of the fast e.p.s.p. in a concentration-dependent way. Hyoscine, pirenzepine and 4-diphenylacetoxy-N-methyl-piperidine (4-DAMP) caused a parallel shift to the right of the agonist dose-response curves. These muscarinic antagonists themselves did not alter the amplitudes of fast e.p.s.p.s evoked by low frequency (0.05-0.1 Hz) stimulation. Antagonist pA2 values (the negative logarithm of the dissociation equilibrium constant) were determined while recording from individual neurones. pA2 values were: pirenzepine 7.0, hyoscine 8.9, and 4-DAMP 8.7. I.p.s.p.s in the submucous plexus were also depressed by muscarinic agonists, and this was competitively reversed by pirenzepine and 4-DAMP, with apparent pA2 values of 6.9 and 8.7 respectively. Muscarinic antagonists alone increased the amplitude of the i.p.s.p. evoked either by single or repeated stimuli. This enhancement was observed with low concentrations of antagonists and did not become greater when the concentrations were increased. Muscarinic agonists depolarized about one-quarter of myenteric and submucous plexus neurones. Low concentrations of pirenzepine antagonized these depolarizations; the pA2 value was 8.4. Cholinergic slow e.p.s.p.s recorded in some myenteric neurones were depressed or abolished by pirenzepine; concentrations that caused 50% inhibition (IC50) for this action ranged from 10 to 60 nM. It is concluded that presynaptic muscarinic receptors, activation of which inhibits the release of acetylcholine and noradrenaline, are the m2 type. Post-synaptic muscarinic receptors, activation of which depolarizes the membrane, are of the m1 type. The results also suggest that acetylcholine may exert a tonic inhibition of noradrenaline release in the submucous plexus through m2 receptors, and mediates the slow e.p.s.p. in the myenteric plexus through m1 receptors.

Action Potentials↗

PubMed1984

In vitro synthesis of ACTH- and beta-endorphin-related substances in the pars distalis of Anolis carolinensis.

In order to investigate the biosynthesis of ACTH- and beta-endorphin-related substances in the pars distalis of Anolis carolinensis, explants of pars distali were incubated for 24 hr in a complete medium which contained [3H]tyrosine. Acid extracts of the incubates were immunoprecipitated with either an affinity-purified ACTH antiserum or an affinity-purified beta-endorphin antiserum and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Three distinct peaks of ACTH-related material were detected. The major peak comigrated with human ACTH(1-39), while two minor peaks corresponded in apparent molecular weight to ACTH biosynthetic intermediate and precursor-sized material. Three peaks of beta-endorphin-related material were also detected. The major peak comigrated with beta-endorphin(1-31), while two minor peaks corresponded to beta-lipotropin (LPH) and precursor-sized material. Sequential immunoprecipitation experiments indicated that the precursor-sized material had antigenic determinants for both ACTH and beta-endorphin. In addition this peak was identical in apparent molecular weight to the common precursor for alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin in the pars intermedia of A. carolinensis (R.M. Dores, Peptides 3, 925-935). Analysis of extracts of reptile pars distalis by gel-filtration chromatography revealed a single peak of naloxone-reversible opiate bioactivity which coeluted with the peak of beta-endorphin-sized immunoreactivity. On a molar basis there is tenfold more opiate bioactivity in the reptile pars distalis than in the reptile pars intermedia.

Adrenocorticotropic Hormone↗

PubMed1984

Quinine blocks a calcium-activated potassium conductance in mammalian enteric neurones.

Quinine (100 microM) abolished the slow calcium-dependent afterhyperpolarization which occurs after an action potential in some neurones of the guinea-pig myenteric and submucous plexus. This occurred without any effect on the amplitude or time course of the action potential itself, or on the faster calcium-independent afterhyperpolarization. Tetraethylammonium did not reduce the slow afterhyperpolarization. Quinine also abolished the hyperpolarization which was evoked by intracellular injection of calcium ions.

Action Potentials↗

PubMed1984

Slow excitatory synaptic potentials recorded from neurones of guinea-pig submucous plexus.

Intracellular recordings made from neurones of guinea-pig submucous plexus revealed three types of synaptic input: cholinergic excitatory synaptic potentials (fast e.p.s.p.s) of 50-80 ms duration, inhibitory synaptic potentials (i.p.s.p.s) of 1 s duration, and non-cholinergic, non-adrenergic slow e.p.s.p.s which lasted for 15-20 s. A single stimulus was sufficient to elicit the slow e.p.s.p. in all neurones in which this synaptic input was present. Slow e.p.s.p.s were recorded in those neurones which also displayed i.p.s.p.s. Both the i.p.s.p. and the slow e.p.s.p. appeared in an all-or-none fashion and were not affected by alterations in the stimulus strength. The inhibitory as well as the slow excitatory synaptic potentials reversed close to the K+ equilibrium potential, indicating that the i.p.s.p. is due to an activation of K+ conductance while the slow e.p.s.p. is due to its inactivation. Evidence is presented which suggests the slow e.p.s.p. may be generated at a synapse located some distance from the soma, presumably at a dendritic location. Only those cells which showed slow e.p.s.p.s responded to substance P with a depolarization which mimicked the slow e.p.s.p.

Action Potentials↗

PubMed1984

Two types of neurones lacking synaptic input in the submucous plexus of guinea-pig small intestine.

Intracellular recordings were made from neurones in the submucous plexus of guinea-pig small intestine. Approximately 20% of all neurones studied appeared to lack synaptic input; two types of neurones without synaptic input were identified. The action potential recorded from one of these types of ganglion cells was followed by a prolonged after-hyperpolarization. The after-hyperpolarization was abolished by Co2+ or Mn2+. A Ca2+ component of the evoked action potential was demonstrated after the Na+ component had been abolished by tetrodotoxin (TTX). The other type of neurone was characterized by a high input resistance (220-320 M omega) and spontaneous action potentials which were unaffected by hexamethonium, curare, atropine or TTX. The ionic basis of the action potentials evoked from spontaneously active cells differed from other enteric neurones. These action potentials exhibited a TTX-insensitive Na+ component as well as a Ca2+ component. It is suggested the spontaneously active neurones may be responsible for the ongoing synaptic activity recorded from many submucous plexus neurones in the absence of stimulation.

Action Potentials↗

PubMed1983

Effects of nifedipine on nerve-evoked action potentials and consequent contractions in rat tail artery.

The effects of nifedipine on the electrical and mechanical activity recorded from the rat tail artery were examined. Intracellular recordings were obtained from the smooth muscle and vessel diameter monitored during nerve stimulation. Nifedipine (0.1-10 microM) depressed contractions elicited by single and repetitive (2 Hz) stimulation by 32-100% but was ineffective in decreasing the amplitude of the associated action potentials. Concentrations greater than or equal to 10 microM caused a slowly developing membrane depolarization. No change in the amplitude of subthreshold excitatory junction potentials was observed at concentrations of nifedipine less than 50 microM when the membrane depolarization was less than 8 mV. At all concentrations examined nifedipine lowered the stimulus intensity required to initiate an action potential. The amplitude of the nerve-evoked action potential recorded in lowered external Ca2+ (1 mM) was slightly increased (5-10%) by nifedipine. However, nifedipine readily reversed the increased amplitudes of the nerve-evoked action potentials and contractions caused by the addition of 20 mM tetraethylammonium chloride in the tail artery. The action potential recorded in normal solution from the guinea pig vas deferens was selectively abolished by nifedipine.

Animals↗

PubMed1982

Correlation between electrical activity and ACTH/beta-endorphin secretion in mouse pituitary tumor cells.

The electrical and secretory activities of mouse pituitary tumor cells (AtT-20/D-16v), which contain and release the ACTH/beta-endorphin family of peptides, were studied by means of intracellular recordings and radioimmunoassays. Injection of depolarizing current pulses evoked action potentials in all cells and the majority (82%) displayed spontaneous action potential activity. Action potentials were found to be calcium-dependent. Barium increased membrane resistance, action potential amplitude and duration, and release of ACTH and beta-endorphin immunoactivity. Isoproterenol increased both action potential frequency and hormone secretion. Raising the external calcium concentration increased the frequency and amplitude of the action potentials and stimulated secretion of ACTH and beta-endorphin immunoactivity. Thus, stimulation of secretory activity in AtT-20 cells was closely correlated with increased electrical activity. However, a complete blockade of action potential activity had no effect on basal hormone secretion in these cells. These results suggest that the mechanisms underlying stimulated hormone secretion are different from those responsible for basal secretory activity. It is proposed that the increased influx of calcium due to the increased action potential frequency initiates the stimulated release of hormone from these cells.

Action Potentials↗

PubMed1980

A comparative study of neuromuscular transmission in several mammalian muscular arteries.

Intracellular recordings were made from the smooth muscle of isolated segments of the rabbit ear artery, rabbit saphenous artery, rat tail artery, and guinea pig mesenteric artery. Resting membrane potentials recorded from cells in all these arteries were the same (-65 to -75 mV) and perivascular nerve stimulation evoked excitatory junction potentials (EJPs). At stimulation frequencies > 0.2 Hz facilitation of the EJPs was observed in all but the rat tail artery; in this artery the amplitude of the second EJP in a train was less than the first for stimulation frequencies between 0.3 and 2.0 Hz. Spontaneous excitatory junction potentials (SEJPs) at frequencies up to 20/min were recorded during all impalements in the rat caudal artery. In rabbit ear, saphenous and guinea pig measenteric arteries single, supramaximal intensity stimuli evoked EJPs which were not associated with any detectable contraction. Facilitation of EJPs during trains of stimuli > 1 Hz gave rise to graded active responses of up to 50 mV in the saphenous and tail arteries whereas all-or-nothing action potentials of 42--50 mV were recorded in both the rabbit ear and guinea pig mesenteric arteries. Such responses were always associated with contraction. Intraluminal distension of the arteries had no effect on the RMP or response to nerve stimulation.

Animals↗

PubMed1980

An electrophysiological analysis of the effects of noradrenaline and alpha-receptor antagonists on neuromuscular transmission in mammalian muscular arteries.

1 The effects of exogenously applied noradrenaline (NA) and alpha-adrenoceptor antagonists on the mechanical and intracellularly recorded responses to perivascular nerve stimulation were examined in the rabbit ear artery, rabbit saphenous artery and rat tail artery. 2 Excitatory junction potentials (e.j.ps) and action potentials recorded from these smooth muscles were not blocked or depressed by phentolamine, phenoxybenzamine, prazosin, or labetolol in concentrations as high as 10 microgram/ml. Phentolamine (1 to 10 microgram/ml) depressed neurally-evoked contractions of the ear and saphenous, but not the tail artery, and also depressed the contractions produced by direct muscle stimulation in the ear and saphenous arteries. Prazosin and labetolol (0.1 to 10 microgram/ml) had no effect on the neurally evoked contractile response in any of the arteries examined. 3 The amplitude of the steady-state e.j.p. during repetitive stimulation at 0.45 to 2 Hz was increased by phentolamine or phenoxybenzamine but not by prazosin or labetolol. Phentolamine and phenoxybenzamine also increased the amplitude of the e.j.p. evoked by a single stimulus in the majority of the preparations. 4 Concentrations of NA greater than or equal to 1 microgram/ml depolarized the smooth muscle while concentrations greater than or equal to 0.5 microgram/ml depressed the amplitude of the e.j.ps recorded from these arteries. alpha-Antagonists did not suppress either the NA-induced membrane depolarization or depression of e.j.ps. 5 These observations call into question the physiological relevance of both pre- and postsynaptic alpha-receptors in regard to adrenergic neuromuscular transmission in muscular arteries.

Action Potentials↗

PubMed1980

Effects of tetraethylammonium chloride on sympathetic neuromuscular transmission in saphenous artery of young rabbits.

1. Excitatory junction potentials and electrotonic potentials were recorded from the smooth muscle of the rabbit saphenous artery using intracellular electrodes. 2. Tetraethylammonium chloride (TEA) in concentrations greater than 3.5 mM caused depolarization. Concentrations greater than 5 mM caused spontaneous electrical activity in the form of excitatory junction potentials (e.j.p.s) and all-or-nothing action potentials which were associated with spontaneous mechanical activity. 3. Concentrations of TEA less than 2.5 mM did not alter the resting potential nor the passive membrane properties of the smooth muscle over a range of +/- 15 mV. 4. The following effects were observed in 2.0 mM-TEA. (a) The minimum stimulus strength required for the initiation of an e.j.p. fell by three to fivefold. (b) Single stimuli that elicited only a small e.j.p. in normal solution evoked an all-or-nothing action potential of up to 70 mV amplitude. (c) Whereas in normal solution e.j.p.s could only be recorded up to 7 mm away from the perivascular stimulating electrode e.j.p.s could be recorded at distances of up to 13 mm. (d) The duration of the e.j.p. was prolonged. 5. Based on these results and the effects of TEA reported for other synapses it is proposed that TEA may act to increase the amount of transmitter released per axon, to increase the duration of release and to cause an increased invasion throughout the autonomic ground plexus by nerve impulses. This would imply that in normal solution, in vitro, the action potential may not propagate throughout the whole length of the terminal axon and its many branches due to failure of conduction at one or more points along the terminal portion of the axon.

Animals↗

PubMedDate not supplied

Biosynthesis of multiple forms of beta-endorphin in the reptile intermediate pituitary.

Fractionation of the beta-endorphin-sized material from freshly dissected reptile intermediate pituitaries by ion exchange chromatography on sulfopropyl Sephadex (SP) revealed at least three distinct forms of immunoreactive beta-endorphin. These forms eluted at 0.25 M NaCl, 0.28 M NaCl, and 0.32 M NaCl and represent respectively, 6%, 65% and 29% of the total immunoreactivity. Only the 0.28 M NaCl peak and the 0.32 M NaCl peak exhibited naloxone reversible opiate bioactivity when tested in the isolated guinea pig ileum bioassay system; taking into account the molar amount of immunoreactive peptides the 0.32 M NaCl peak was 6 fold more potent than the 0.28 M NaCl peak. Intermediate pituitaries in culture were incubated with either [3H]tyrosine, [3H]arginine, or [35S]methionine for periods up to 24 hours and beta-endorphin-sized peptides were prepared by immunoprecipitation and gel filtration. Fractionation of the labeled beta-endorphin-sized peptides by ion exchange chromatography yielded profiles nearly identical to the immunoassay analyses of freshly dissected tissue. Further analysis of the major labeled forms of reptile beta-endorphin by chromatography on Sephadex G-50 equilibrated in 6 M guanidine HCl indicated that the 0.32 M NaCl peak had an apparent molecular weight of 3500 +/- 100 and the 0.28 M NaCl peak had an apparent molecular weight of 3200 +/- 100. Furthermore, pulse/chase experiments showed that the 0.32 M NaCl peak was the precursor for the 0.28 M NaCl peak. These results coupled with the relative opiate bioactivities of the major argue that the principal post-translational modification of reptile beta-endorphin is COOH-terminal proteolytic cleavage.

Animals↗

PubMedDate not supplied

Expression of ligand-gated ion channels with the Semliki Forest virus expression system.

Two types of ligand-gated ion channels were expressed with the Semliki Forest virus (SFV) expression system. The cDNAs for mouse serotonin 5-HT3 receptor and rat and human purinoreceptor P2x subtypes were introduced into the pSFV1 vector. In vitro transcribed RNAs were coelectroporated with pSFV-Helper2 RNA into BHK cells, where in vivo packaging resulted in high titer SFV-5-HT3 and SFV-P2x virus stocks. Infection of BHK, CHO and RIN cells resulted in high-level expression of recombinant receptors. Saturation binding analysis indicated the presence of more than 3 x 10(6) 5-HT3 receptors per cell. Binding studies on isolated membranes yielded from 10 to 60 pmol of either 5-HT3 or P2x receptor per mg protein. Functional responses to the P2x receptors were demonstrated in SFV-infected CHO cells by Ca2+ mobilization or by 45Ca2+ influx. High amplitude electrophysiological responses were also detected for both SFV-5-HT3 and SFV-P2x infected CHO cells in whole-cell patch clamp recordings. To facilitate the purification procedure of SFV-expressed recombinant receptors a histidine tag was introduced at the C-terminus of the 5-HT3 receptor. This 5-HT3His receptor showed high levels of expression, specific binding and high amplitude electrophysiological responses. For large scale expression the BHK cells were adapted to suspension culture and were efficiently infected in a 11.5 liter fermentor culture with SFV-5-HT3His resulting in high-level expression, 52 pmol receptor per mg protein corresponding to 3.2 x 10(6) receptors per cell.

Adenosine Triphosphate↗