Nerves In Rat Tail Artery Research Articles

Adenosine receptors involved in modulation of noradrenaline release in isolated rat tail artery

Adenosine receptors involved in the modulation of noradrenaline release from postganglionic sympathetic nerves in rat tail artery were characterized by studying the effects of adenosine-receptor agonists and antagonists on electrically evoked tritium overflow (100 pulses, 5 Hz) and by immunohistochemistry. The adenosine A 1 receptor-selective agonist N 6-cyclopentyladenosine (CPA; 1–100 nM) and the non-selective adenosine receptor agonist N-ethylcarboxamidoadenosine (NECA; 1–10 μM) decreased tritium overflow. These effects were blocked by the adenosine A 1 receptor-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 30 nM). The adenosine A 2A receptor-selective agonist 2- p–(2-carboxyethyl)phenethylamino-5′- N-ethylcarboxamido adenosine (CGS 21680; 1–100 nM) enhanced tritium overflow, an effect blocked by the adenosine A 2A receptor-selective antagonist 5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo-[4,3- e]-1,2,4-triazolo[1,5- c]pyrimidine (SCH 58261; 20 nM) but not changed by the adenosine A 2B receptor-selective antagonist N-(4-acetylphenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1 H-purin-8-yl) phenoxy]acetamide (MRS 1706; 20 nM). In the presence of DPCPX (30 nM), NECA enhanced tritium overflow, an effect abolished by MRS 1706 but not influenced by SCH 58261. Immunohistochemistry revealed immunoreactivity for all adenosine-receptor subtypes. Areas of co-localization were found for neurofilament with adenosine A 1, A 2A and A 2B but not A 3 receptors. In conclusion, the present study provides functional and morphological evidence for the occurrence of multiple adenosine receptor-mediated modulation of noradrenaline release in the rat tail: inhibition mediated by adenosine A 1 receptors and facilitation mediated by both adenosine A 2A and A 2B receptors.

Facilitation and depression of ATP and noradrenaline release from sympathetic nerves of rat tail artery.

1. Excitatory junction currents (EJCs) were used to measure ATP release; noradrenaline (NA) oxidation currents and fractional overflow of labelled NA, [3H]NA, were used to monitor the release of endogenous and exogenous NA, respectively, from post-ganglionic sympathetic nerves of rat tail artery. 2. During nerve stimulation with 100 pulses at 5-20 Hz the EJCs initially grew in size (maximally by 23 %, at 2-10 Hz), and then depressed, maximally by 68 % at 20 Hz. 3. The peak amplitude of NA oxidation currents in response to nerve stimulation with 100 pulses at 2-20 Hz grew in size with frequency, while the area was independent of frequency and roughly constant. 4. The size of the NA oxidation currents evoked by nerve stimulation with 4-100 pulses at 20 Hz grew linearly with train length between pulses 4-16. Between pulses 20-100 there was a train length-dependent depression of the signal. 5. Fractional overflow of [3H]NA in response to nerve stimulation with 5-100 pulses at 20 Hz behaved similarly to the EJCs. It initially grew roughly linearly between pulses 5-25, and then showed a dramatic depression similar to that of the EJCs. 6. The alpha2-adrenoceptor antagonists rauwolscine and yohimbine increased the overflow of [3H]NA and the amplitude of NA oxidation currents, but not that of the EJCs. 7. It is concluded that during high-frequency stimulation (i) the release of ATP and NA is first briefly facilitated then markedly depressed, (ii) facilitation and depression of the two transmitters are similar in magnitude and time course, and (iii) alpha2-adrenoceptor antagonists differentially modify EJCs and the NA signals. The results obtained in the absence of drugs are compatible with the hypothesis that ATP and NA are released in parallel, while the effects of alpha2-adrenoceptor antagonists seem to suggest dissociated release.

Paired pulse analysis of ATP and noradrenaline release from sympathetic nerves of rat tail artery and mouse vas deferens: effects of K+ channel blockers.

1. The paired pulse stimulus paradigm - two pulses of equal strength delivered at variable interpulse intervals was used to study the release of ATP and noradrenaline (NA) from post ganglionic sympathetic nerves of rat tail artery and mouse vas deferens. 2. Excitatory junction currents (EJCs) were used to measure the release of ATP, and differential pulse amperometry to measure that of NA. 3. At interpulse intervals of 0.1 - 1 s paired pulse stimulation caused an increase in the size of the second EJC, both in rat tail artery and mouse vas deferens. As the interpulse interval was increased to 10 s or more, the two EJCs became of equal size. 4. In both preparations the K+ channel blockers tetraethylammonium (TEA, 20 mM) and 4-aminopyridine (4-AP, 1 mM) prolonged the duration of the nerve terminal spike and greatly amplified the first EJC of the pair. 5. In the presence of TEA and 4-AP in rat tail artery paired pulse stimulation caused a dramatic depression of the second EJC without markedly affecting the nerve terminal spike. The depression of the second EJC decreased with increasing interpulse intervals, and also when external Ca2+ was reduced to 0.2 mM. In mouse vas deferens, TEA and 4-AP caused only a modest depression of the second EJC. 6. In rat tail artery in the presence of TEA and 4-AP paired pulse stimulation caused a depression of the NA oxidation current evoked by the second pulse, which was similar in magnitude and time course to that of the EJC. Similar TEA and 4-AP induced depression of the second pulse response was also observed when the purinergic and noradrenergic components of the contractile response were investigated. 7. The results show that in rat tail artery K+ channel blockers cause a dramatic paired pulse depression of the release of ATP and NA. The similarity in the depression of the EJC, the NA oxidation current, and the purinergic and noradrenergic components of the contractile response is compatible with the hypothesis that ATP and NA are released in parallel from the same neuronal sources.

Persistent release of noradrenaline caused by anticancer drug 4′-epidoxorubicin in rat tail artery in vitro

Anthracycline derivatives including 4′-epidoxorubicin are known to cause cardiovascular side effects. In this study we examined the effects of 4′-epidoxorubicin on sympathetic nerves of rat tail artery in vitro. Treatment with 4′-epidoxorubicin at concentrations higher than 10 μM gradually increased the resting tension of the arterial strips, an effect which was greatly enhanced by subsequent addition of 10 μM cocaine. This increase of the resting tension by 4′-epidoxorubicin was prevented by prazosin, suppressed in the arterial strips of reserpine-pretreated rats, and reduced by superoxide dismutase. However, tetrodotoxin and histamine receptor antagonists (diphenhydramine and cimetidine) failed to influence it. The contractile response to electrical sympathetic stimulation was slightly attenuated by 30 μM 4′-epidoxorubicin. 4′-Epidoxorubicin did not shift the concentration–response curve for noradrenaline. In the superfusion experiments, the basal release of noradrenaline was increased approximately five-fold by 30 μM 4′-epidoxorubicin, and this increase was not inhibited by 0.1 μM prazosin, 0.5 μM tetrodotoxin, 10 μM cocaine or Ca 2+-free medium. Noradrenaline release evoked by electrical stimulation was gradually suppressed by 30 μM 4′-epidoxorubicin treatment. These results suggest that 4′-epidoxorubicin directly acts on the sympathetic nerve to cause persistent release of noradrenaline in rat tail artery.

Adrenergic Nerve Smooth Endoplasmic Reticulum Calcium Buffering Declines with Age

Calcium buffering capacity declines with age in sympathetic nerves of rat tail artery. To test whether smooth endoplasmic reticulum (SER) calcium buffering declines with age, effects of two SER calcium-ATPase inhibitors on norepinephrine release and intracellular calcium were determined. Thapsigargin or cyclopiazonic acid caused a significant increase in stimulation-evoked norepinephrine release from 6 month tail arteries with much less effect in 20 months. In isolated superior cervical ganglion cells, the rate of rise of calcium with K +-depolarization increased only in young cells with either cyclopiazonic acid or thapsigargin, with no effect in the old. In young cells, cyclopiazonic acid significantly influenced time to peak, rate of decline, and time to basal of K +-evoked calcium transients, but had no effect in old cells. Thapsigargin caused a significant increase in rate of decline in young, but not old, cells. These differential effects suggest an age-related decline in function of SER calcium buffering mechanisms in the sympathetic nervous system causing older nerves to become more reliant on mitochondria to buffer calcium.

A novel electrophysiological approach to monitor pulse by pulse the concentration of released noradrenaline at the presynaptic alpha 2-adrenoceptors of sympathetic nerves in rat tail artery.

The excitatory junction current (EJC) evoked by electrical stimulation of postganglionic sympathetic nerves of rat tail artery with 100 pulses at 2 Hz, at 1.3 mmol/l external Ca2+, was used as a measure of the per pulse release of ATP. In controls the EJCs were initially facilitated, then gradually depressed during the stimulus train. The first EJC was slightly depressed by the alpha 2-adrenoceptor antagonist yohimbine, but starting from the 4th pulse the EJCs were enhanced. Yohimbine increased the early facilitation without markedly modifying the subsequent depression. The yohimbine-induced enhancement of EJCs caused by pulses 11-100 was, thus, constant. The noradrenaline reuptake blocker cocaine depressed the EJCs, abolished the early facilitation and slightly enhanced the depression. These effects of cocaine were reversed by further addition of yohimbine. The alpha 2-adrenoceptor agonist xylazine (1 and 10 mumol/l) dose dependently depressed the EJCs starting from the first pulse. The inhibitory effect of 1 mumol/l xylazine, but not that of 10 mumol/l xylazine, declined with train length. The inhibition of individual EJCs caused by activation of presynaptic alpha 2-adrenoceptors was used to monitor the concentration of released noradrenaline at these receptors. The ratio of individual EJCs in the presence and absence of yohimbine was assumed to reflect, pulse by pulse, the relative concentration of released noradrenaline at the presynaptic alpha 2-adrenoceptors, and hence termed [NA]alpha 2. For comparison, the concentration of endogenous noradrenaline was monitored electrochemically by differential pulse amperometry with a carbon fibre microelectrode; this signal is termed [NA]CF. [NA]alpha 2 and [NA]CF grew during the first 7-10 or 14-16 pulses, respectively, and then remained relatively constant throughout the stimulus train. Cocaine caused [NA]alpha 2 and [NA]CF to continue to grow during the first 35 and 50 pulses, and enhanced their peak levels by 180% and 320%, respectively. For comparison with the effects on the EJCs mediated via presynaptic alpha 2-adrenoceptors, those caused by varying external Ca2+ level were examined. At 0.65 mmol/l Ca2+ the amplitude of the first EJC was smaller than that at 1.3 mmol/l Ca2+, but the facilitation of later EJCs was enhanced and the subsequent depression reduced. An increase in external Ca2+ to 2.6 mmol/l had the opposite effects. All effects on EJCs caused by changes in external Ca2+ were maximal for the first EJC and then declined with the train length.(ABSTRACT TRUNCATED AT 400 WORDS)

Intermittent release of noradrenaline by single pulses and release during short trains at high frequencies from sympathetic nerves in rat tail artery

As shown by electrophysiological analysis, the release of the sympathetic co-transmitter adenosine 5′-triphosphate (ATP) from individual release sites is monoquantal and intermittent; the average release probability may be as low as 0.01. 1–3 Indirect evidence from biochemical studies of noradrenaline overflow is compatible with a similar monoquantal, low probability release of noradrenaline as well. 10 In the present study our first aim was to address this issue more directly in rat tail artery, using continuous amperometry to monitor in real time the release of noradrenaline from a relatively small number of sympathetic nerve varicosities. The results seem to provide the first direct evidence that noradrenaline, similarly to ATP, may be released intermittently during nerve stimulation at low frequency. Our second aim was to use the same technique to study the release of noradrenaline caused by nerve stimulation with single pulses or short trains (two to eight pulses) at high frequencies. The results show that during stimulation at 20 Hz the peak amplitude of the noradrenaline oxidation current response grew linearly with the train length, but at 50 Hz the curve describing this growth was sigmoid in shape.

ATP as a sympathetic co‐transmitter in rat vasomotor nerves‐further evidence that individual release sites respond to nerve impulses by intermittent release of single quanta

A combination of intra- and extracellular recording was used to study neurotransmitter release in sympathetic vasomotor fibres in rat femoral and mesenteric arteries. The results show that neurotransmission in these preparations is similar to that in the 'short' sympathetic nerves in guinea-pig vas deferens and the 'long' sympathetic nerves in rat tail artery in the following respects: (1) The intracellularly recorded excitatory junction potentials (EJPs) and the extracellularly recorded junction currents (EJCs) presumably are caused by ATP secreted as a sympathetic co-transmitter. (2) The stimulus-evoked and spontaneous EJCs share the same brief time-course, which is similar to that of spontaneous EJPs, but much briefer than that of stimulus-evoked EJPs. (3) 'Successful' nerve impulses appear to release single transmitter quanta. (4) The probability of activation of individual release sites is low (0.002-0.02). (5) The low release probability cannot be accounted for by failure of the nerve impulse to invade the terminals. Moreover, it is also shown that application of tetrodotoxin to the medium within the recording electrode effectively abolishes transmitter secretion in the area enclosed by the tip of the electrode, indicating that the effective length constant for a passively propagating nerve action potential is probably very small and that activation of the release mechanisms in 'long' sympathetic nerve fibres seems to require that the varicosities are actively invaded.

Cd2+ may inhibit ATP secretion from sympathetic nerves in rat tail artery by an 'upstream' effect without blocking the Ca2+ component of the action potential in the terminals.

Acta Physiologica ScandinavicaVolume 136, Issue 2 p. 299-300 Cd2+ may inhibit ATP secretion from sympathetic nerves in rat tail artery by an ‘upstream’ effect without blocking the Ca2+ component of the action potential in the terminals L. STJÄRNE, Corresponding Author L. STJÄRNE Department of Physiology, Karolinska Institute, Stockholm, SwedenDepartment of Physiology, Karolinska Institute, S-10401 Stockholm, Sweden.Search for more papers by this authorM. MSGHINA, M. MSGHINA Department of Physiology, Karolinska Institute, Stockholm, SwedenSearch for more papers by this authorE. STJÄRNE, E. STJÄRNE Department of Physiology, Karolinska Institute, Stockholm, SwedenSearch for more papers by this authorP. ÅSTRAND, P. ÅSTRAND Department of Physiology, Karolinska Institute, Stockholm, SwedenSearch for more papers by this author L. STJÄRNE, Corresponding Author L. STJÄRNE Department of Physiology, Karolinska Institute, Stockholm, SwedenDepartment of Physiology, Karolinska Institute, S-10401 Stockholm, Sweden.Search for more papers by this authorM. MSGHINA, M. MSGHINA Department of Physiology, Karolinska Institute, Stockholm, SwedenSearch for more papers by this authorE. STJÄRNE, E. STJÄRNE Department of Physiology, Karolinska Institute, Stockholm, SwedenSearch for more papers by this authorP. ÅSTRAND, P. ÅSTRAND Department of Physiology, Karolinska Institute, Stockholm, SwedenSearch for more papers by this author First published: June 1989 https://doi.org/10.1111/j.1748-1716.1989.tb08669.xCitations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume136, Issue2June 1989Pages 299-300 RelatedInformation

On the secretory activity of single varicosities in the sympathetic nerves innervating the rat tail artery.

1. Nerve terminal impulses (NTIs) and spontaneous or stimulus-evoked excitatory junction currents (SEJCs or EJCs), reflecting secretion of transmitter quanta from release sites in the sympathetic nerves of rat tail artery, were recorded by extracellular electrodes. 2. The release of transmitter quanta from single varicosities was analysed on a pulse-by-pulse basis. 3. Since the SEJCs were tetrodotoxin-resistant, and hence probably caused by single quanta, they were employed to analyse the quantal content of EJCs. 4. In the majority of recordings, EJCs were large compared to SEJCs from the same attachment, and preceded by prominent NTIs. This type of activity appeared to reflect simultaneous activation of several nerve fibres and numerous varicosities. 5. By focal stimulation, it was usually possible to improve the resolution by examining spots in which a large proportion of the suprathreshold stimuli failed to cause EJCs. Here, averaged NTIs preceding large EJCs were indistinguishable from averaged NTIs not followed by EJCs. Thus, failure of invasion by the nerve impulse was not a cause of the frequent secretory failure. 6. In these attachments the amplitude distribution of nerve stimulus-evoked EJCs was similar to that of the SEJCs and many individual EJCs could be matched in amplitude and time course by SEJCs. Thus, transmitter secretion from these sympathetic nerve varicosities seems to be basically monoquantal. 7. Under conditions when all EJCs were smaller than or equal to the largest SEJCs some characteristic EJC profiles appeared only a few times in response to several hundred suprathreshold stimuli at low frequency (0.5-1 Hz). Using tentatively these EJCs as 'fingerprints' of single quanta from particular release sites, the probability for activation of individual release sites ranges from 0.002 to 0.02.