Presence Of Norepinephrine Research Articles

Immunohistochemical and histochemical evidence for the presence of noradrenaline, serotonin and gamma-aminobutyric acid in chief cells of the mouse carotid body

Immunohistochemical and histochemical evidence for the presence of noradrenaline, serotonin and gamma-aminobutyric acid in chief cells of the mouse carotid body

Effects of caffeine on intracellular sodium activity in cardiac Purkinje fibres: relation to force.

1. An increase in cytoplasmic calcium by caffeine would lead to Ca extrusion via the Na/Ca exchange. The hypotheses were investigated that, as a consequence, caffeine might increase intracellular sodium activity (aiNa) and that the relation between aiNa and force might be conditioned by the Ca load. 2. Action potential, aiNa and contractile force were recorded in sheep Purkinje fibres during exposure to caffeine under conditions that decrease or increase the Ca load by different mechanisms. 3. In Tyrode solution, caffeine (8 mM) increased aiNa from 8.05 +/- 0.20 to 10.52 +/- 0.40 mM (+30.5%) and had a triphasic effect on force: an initial transient increase (+93.6%), a subsequent decrease (-37.1%) (negative inotropy) and slow partial recovery (+8.9%). 4. Decreasing the Ca load by means of manganese (1 mM) decreased aiNa and force. Adding caffeine re-increased aiNa and no longer caused a negative inotropic action. Cadmium (0.2 mM) also decreased aiNa, and caffeine reincreased it although far less than in Tyrode solution. 5. High [K]o (10 mM) and tetrodotoxin (5 microM) decreased aiNa as well as force. In their presence, caffeine re-increased aiNa and no longer had a negative inotropic action. 6. Increasing the Ca load by means of high [Ca]o (8.1 mM) increased force (+195%) and decreased aiNa, (-20.3%). Adding caffeine re-increased aiNa (+28.1%), but immediately decreased force (-32.3%). 7. Addition of pyruvate (10 mM) to caffeine increased force, as it does in the presence of Ca overload. 8. Noradrenaline (0.1-1 microM) decreased aiNa and increased contractile force. In its presence, caffeine decreased aiNa further and increased force. 9. It is concluded that caffeine increases aiNa, even during the negative inotropic effect. The decrease in force appears to depend on Ca load. Thus, caffeine no longer decreases force under conditions that decrease Ca load (Mn, high [K]0, TTX) and immediately decreases force when the Ca load is increased(high [Ca]0). However, in the presence of noradrenaline, caffeine decreases aiNa and markedly increases force, as the Ca load is increased, but Ca can be removed from the cytoplasm into the SR.

Stabilization of the mRNA for the uncoupling protein thermogenin by transcriptional/translational blockade and by noradrenaline in brown adipocytes differentiated in culture: a degradation factor induced by cessation of stimulation?

The stability of the mRNA coding for the uncoupling protein thermogenin was investigated in mouse brown-fat cells differentiated in culture. After 7 days in culture, the cells were stimulated for 24 h with noradrenaline, and a high level of thermogenin mRNA was then observed. If noradrenaline treatment was continued, the mRNA level remained high, but, upon withdrawal of noradrenaline, the level decreased rapidly, with a half-life of only 2.7 h. The presence of transcriptional (actinomycin) or translational (cycloheximide) inhibitors prolonged the apparent half-life by about 50%. The presence of noradrenaline during transcriptional blockade led to a further stabilization of thermogenin mRNA. It was concluded that an induced (or short-lived) gene product is important for thermogenin mRNA degradation. Direct interaction of noradrenaline with the cultured brown adipocytes could apparently not mimic the paradoxical destabilization of thermogenin mRNA in vivo, previously observed in the cold-exposed mouse [Jacobsson, Cannon and Nedergaard (1987) FEBS Lett. 244, 353-356], indicating significant differences between the systems in vitro and in vivo.

Vasodilation and mechanism of action of propofol in porcine coronary artery.

A decrease in myocardial perfusion pressure may reduce myocardial blood flow. However, it may not significantly affect myocardial perfusion when in presence of a concurrent coronary artery vasodilation. However, the effects of propofol in coronary arteries are not well determined. In this study, the effects of propofol on porcine coronary artery responses to vasoactive agents that operate through voltage- and receptor-mediated calcium mechanisms were investigated. Hearts of adult pigs (n = 103) were obtained from a slaughter house, and the left anterior descending coronary arteries were dissected. The arteries were cut into vessel rings and prepared with and without the endothelium organ chambers filled with buffered salt solution. The effect of propofol (10(-7), 10(-6), 10(-5), and 10(-4) M) on vascular smooth muscle contraction caused by intracellular Ca(2+)-influx through voltage- and receptor-mediated mechanism also was studied at a cellular level. Propofol relaxed coronary rings that were contracted by KCl, norepinephrine (NE), serotonin (5-HT), or carbachol (CCh). The minimal concentrations of propofol that produced significant vasorelaxation ranged from 3.16 x 10(-7) M to 3.16 x 10(-6) M. Vasodilation was more pronounced in rings contracted by NE, 5-HT, and CCh than by KCl. Propofol (10(-5) M) attenuated coronary vasoconstriction in response to cumulative concentrations of KCl, NE, 5-HT, and acetylcholine. Maximal contractions produced by NE and 5-HT were inhibited to a greater degree than contractions produced by KCl. Propofol at concentrations of 10(-5) M and higher attenuated a contraction in response to CaCl2 in vascular rings depolarized by KCl, but concentrations of 10-M did not attenuate contractions. Vasoconstriction in response to calcium entry in the presence of NE (and nifedipine 10(-6) M) was attenuated by propofol at concentrations of 10(-6) M and higher. Caffeine-induced contraction, caused by intracellular calcium release, was attenuated only at 10(-4) M of propofol. Propofol possesses vasodilator effect and attenuates the effects of vasoconstrictor agents in porcine coronary artery. Further, an antagonism of calcium channels may be responsible for these effects of propofol.

Contribution of both nitric oxide and a change in membrane potential to acetylcholine‐induced relaxation in the rat small mesenteric artery

1. Acetylcholine stimulated repolarization and relaxation in isolated segments of rat small mesenteric artery (D100 = 325 +/- 9 microns) in which the smooth muscle cells were depolarized and contracted by submaximal concentrations of noradrenaline (0.75-2.5 microM). There was no significant difference either in the time taken to initiate relaxation or hyperpolarization, or for these parameters to reach maximum in response to acetylcholine. 2. The nitric oxide synthase inhibitor, NG-nitro L-arginine methyl ester (L-NAME, 100 microM) reduced the pD2 for acetylcholine-induced relaxation from 7.5 to 7 and depressed the maximum relaxation from 89% to 68% in tissues stimulated with noradrenaline. The pD2 for smooth muscle repolarization in these experiments was also reduced (7.4 to 6.6) but the maximum change in membrane potential in response to acetylcholine was unaltered. The increase in potential now clearly preceded relaxation by 3.7 s (to initiation) and 4.7 s (to maximum). 3. In the presence of noradrenaline and a raised potassium concentration (25 mM), the repolarization to acetylcholine was markedly attenuated. Simultaneous tension measurements also revealed a marked reduction in the maximal relaxation to acetylcholine, but the pD2 was unchanged at 7.4. 4. The residual relaxation recorded in the absence of marked repolarization (in the presence of noradrenaline and 25 mM potassium) was abolished by the addition of 100 microM L-NAME. 5. Nitric oxide gas in solution (0.2-2.2 microM; NOg) relaxed artery segments precontracted with noradrenaline. The magnitude of relaxation to NOg was not altered in the presence of noradrenaline and 25 mM potassium. 6. These data provide additional evidence that acetylcholine-evoked endothelium-dependent increases in membrane potential provide a major mechanism for smooth muscle relaxation in the mesenteric artery.They also show that voltage-dependent and independent (initiated by NO) mechanisms can both contribute to relaxation, and suggest that NO may modulate the increase in membrane potential or the release of a hyperpolarizing factor.

Vasoactivity of prostanoids in the trout (Oncorhynchus mykiss) coronary system: modification by noradrenaline

An isolated non-working trout heart, cannulated through the coronary artery and perfused with oxygenated saline with a coronary pressure head of 3.0 kPa has been used in this study. Effects on the coronar resistance of catecholamines, thromboxanes (TXs) and prostacyclin (PGI2) were analyzed. The effects of PGI2 and TXs in presence of noradrenaline were also evaluated. Both adrenaline and noradrenaline vasoconstrict the trout coronary system, noradrenaline being more potent than adrenaline. TXA2 induces 45% vasoconstriction at 10(-6)M, while TXB2 at the same concentration is a slight vasodilator. PGI2 acts as a weak vasodilator (about 20% decrease in resistance at 10(-6)M). In presence of 10(-7)M noradrenaline, 10(-8)M TXA2 reduces the vasoconstriction induced by the catecholamine alone from 60% to about 15%. Under similar conditions, 10(-9)M PGI2 potentiates the vasoconstrictive response induced by noradrenaline while a much higher PGI2 concentration (10(-6)M) completely abolishes the vasoconstriction. The β-receptor antagonist propranolol induces vasoconstriction, and 10(-9)M PGI2 in presence of propranolol further increases the vasoconstriction. The α-receptor antagonist phentolamine induces vasodilation and 10(-9)M PGI2 does not affect coronary resistance induced by phentolamine. These results imply a possible interaction between noradrenaline and prostanoids (TXs and PGI2) in the vasomotion of trout coronary system.

Triiodothyronine induces the expression of the uncoupling protein in long term fetal rat brown adipocyte primary cultures: role of nuclear thyroid hormone receptor expression.

Fetal rat brown adipocytes at the beginning of culture showed a minimal T3 nuclear binding capacity and very low expression of the c-erbA genes, with low steady state levels of the mRNA forms beta-type and 5.5- and 2.6-kilobase (kb) alpha-types. The levels of these mRNA species increased after 7 days in culture in the presence of thyroid hormone-depleted serum; however, no significant increase in nuclear T3-binding capacity was observed. The addition of T3 incremented the abundance of the c-erbA beta-mRNA, induced the appearance of the 6.6-kb c-erbA alpha-mRNA and increased the nuclear T3-binding capacity by 30-fold. Parallel analysis of the uncoupling protein (UCP) mRNA, immunoreactive UCP, and functional UCP (detected by its ability to bind GDP) demonstrated that T3 induced the expression of the UCP gene in long term treated fetal brown adipocytes in culture. The presence of noradrenaline, a positive control for UCP expression, increased only the level of expression of the 5.5-kb c-erbA alpha-mRNA, but values for nuclear T3-binding capacity similar to those obtained in T3-treated cells were observed. Simultaneous addition of both hormones gave a pattern of expression of the c-erbA-mRNA forms similar to those obtained with these agents individually, and no further increment in their separate effects was observed on the nuclear T3-binding capacity and UCP expression.

INTERACTIONS BETWEEN 5‐HYDROXYTRYPTAMINE, NORADRENALINE AND THE THROMBOXANE‐A2 MIMETIC U44069 IN THE MARMOSET ISOLATED AORTA

1. The effects of 5-hydroxytryptamine (5-HT) in the absence and presence of noradrenaline (NA) or the thromboxane-A2 mimetic, U44069, were investigated in ring preparations of marmoset aorta. 2. 5-HT (0.001-10 mumol/L) produced little or no contractile response in preparations at basal tone. When the tone was elevated to 50% of maximum with NA the predominant response to 5-HT was relaxation. The 5-HT2 receptor antagonist LY53857 (0.1 mumol/L) unmasked a contractile response to low concentrations of 5-HT (0.01-1.0 mumol/L) and reduced relaxation to high concentrations of 5-HT (1.0-10 mumol/L) in vessels precontracted with NA. 3. In U44069-contracted vessels, 5-HT was contractile in the range 0.01-1 mumol/L and relaxant in concentrations of 6.0-10.0 mumol/L. Ketanserin (1.0 mumol/L) had no effect on the contraction or relaxation to 5-HT. 4. The relaxant response to 5-HT was not significantly diminished in endothelium-impaired arteries. 5. In conclusion, 5-HT exerts complex inhibitory and excitatory actions on the marmoset aorta. The inhibitory actions are not endothelium-dependent and the excitatory actions do not appear to involve the 5-HT2 receptor.

Formation and electrophysiological actions of the arachidonic acid metabolites, hepoxilins, at nanomolar concentrations in rat hippocampal slices

Metabolites of arachidonic acid are known to be formed in the mammalian central nervous system. When intact hippocampal slices were incubated in artificial cerebrospinal fluid, 12-hydroxyeicosatetraenoic acid and two isomers of hepoxilin A 3 (8 R and 8 S) were released as measured by gas chromatography-mass spectrometry. These compounds were released in greater amounts in the presence of noradrenaline or when arachidonic acid was added to the slices. The neuronal actions of chemically derived preparations of 8 R and 8 S hepoxilins and the glutathione conjugate, hepoxilin A 3-C, were examined using intracellular and whole-cell electrophysiological recordings in hippocampal CA1 neurons in vitro. All compounds had the excitatory effects of lowering spike threshold and decreasing spike frequency adaptation, and the inhibitory actions of membrane hyperpolarization, enhanced postspike train afterhyperpolarizations and increased inhibitory postsynaptic potentials or currents. A synthetic analog of hepoxilin A 3-C, in which the glutathione moiety is placed at carbon position 9 instead of carbon position 11 as in hepoxilin A 3-C, was inactive. The actions of the hepoxilins showed a sharp dose-response relationship, with minimal threshold or no effect at 3 nM ( n = 21) and maximal effects at 10 nM ( n = 33). There were no significant differences between the responses to either the 8 R or 8 S isomers, or between hepoxilin A 3 and hepoxilin A 3-C. These data suggest that hepoxilins formed by the brain have significant neuromodulatory actions.

Involvement of endothelium-derived NO in the basal tone and in the vasodilator responses to muscarinic agonists in the rat isolated mesenteric arterial bed.

To investigate the involvement of nitric oxide (NO) derived from endothelial cells in the control of vascular tone in the rat mesenteric vascular bed, the effects of different procedures known to interfere with the NO-cyclic GMP pathway were evaluated both on the basal tone and on the vasodilatory responses to four muscarinic agonists. To this aim, rat isolated mesenteric vascular beds were perfused at constant pressure. Water infusion significantly increased the resting perfusion pressure whereas L-NOARG, L-NAME and methylene blue were devoid of effect. In noradrenaline-preconstricted vascular bed, the perfusion pressure was significantly increased after water or L-NAME infusion. The vasodilator response induced by subsequent addition of acetylcholine in bolus was not significantly modified by pre-treatment with indomethacin but was significantly reduced by water infusion. Responses to acetylcholine and to three other muscarinic agonists--carbachol, oxotremorine or McNeil A 343--were assessed. Incubation with L-NAME did not modify the initial peak falls of the agonists except for McNeil A 343, whereas it significantly reduced the area under the pressure trace for all the substances. The latter effect was reversed after a subsequent incubation with L-Arginine. Finally, L-NAME strongly and significantly increased the drop in perfusion pressure and the area under the pressure trace following bolus of glyceryl trinitrate. These results suggest that in the mesenteric arterial bed of the rat, which can be considered as a resistant arteries preparation, basal tone appears to be controlled by a factor other than NO. Moreover, the vasodilator responses of muscarinic agonists are affected by L-NAME in their second late sustained phase only, which probably relies on a de novo synthesis of endothelium derived-NO. Finally, endothelium derived-NO exerts inhibitory effects both on the sensitivity of the vascular smooth muscle to glyceryl trinitrate and on the magnitude of its contraction in the presence of noradrenaline, two types of effects which are sensitive to L-NAME.

Precollicular decerebration reduces the pressor responses evoked by stimulation of rostral pons but not medulla in cats

In 30 cats under chloralose (40 mg/kg) and urethane (400 mg/kg) anesthesia, the ponto-medullary region involved in cardiovascular integration were stimulated by rectangular pulses (0.5 ms, 80 or 5 Hz, 100 to 200 μA) and/or by microinjection of sodium glutamate (Glu, 0.25–0.5 M, 70–200 nl). Changes of systemic arterial blood pressure (SAP) and renal sympathetic nerve activity (RNA) following stimulation were compared before and after precollicular decerebration. Precollicular decerebration itself resulted in an immediate but brief (5 to 15 min) hypotension with a decrease in SAP ranging from 40 to 100 mmHg. Stimulation of the lateral tegmental field (FTL) produced depressor responses. After precollicular decerebration, the stimulation induced depressor responses were either abolished or converted to mild pressor responses. Stimulation of the dorsal gigantocellular tegmental field-periventricular grey (dFTG-PVG) produced pressor responses. These responses were abolished after precollicular decerebration without exception. On the other hand, precollicular decerebration did not reduce pressor responses produced by stimulation of the ventrolateral medulla (VLM) and the dorsal medulla (DM). In 7 additional cats killed with an overdose of pentobarbital, the brain stem were processed for dopamine β-hydroxylase (DBH). The pressor areas of the VLM and DM were DBH positive, indicating the presence of norepinephrine, while the dFTG-PVG and FTL were not. These findings suggest that the depressor mechanism of the FTL and the pressor mechanism of the dFTG, but not of the VLM or DM depend on actions of the brain structures rostral to superior colliculi.

Role of Intracellular Sodium Activity in the Control of Contraction in Cardiac Purkinje Fibers.

The role of intracellular sodium activity (a(i)(Na)) in the control of force was studied in sheep cardiac Purkinje fibers exposed to norepinephrine (NE) and high [Ca](o) in the absence and presence of overdrive or of a low concentration of strophanthidin. Both NE and high [Ca](o) decrease a(i)(Na) and increae force, while overdrive increases and low strophanthidin decreases both parameters. In the presence of NE, overdrive increases a(i)(Na) less than force and is followed by a more pronounced undershoot in a(i)(Na) and force. In contrast, in high [Ca](o) overdrive increases a(i)(Na) more than force and is followed by a less pronounced undershoot in a(i)(Na) and force than in NE. High [Ca](o) increases force to a peak, but then the decreasing a(i)(Na) reduces force. In all these conditions, a(i)(Na) determines force changes during recovery from overdrive. NE and high [Ca](o) decrease a(i)(Na) less and increase force more in low strophanthidin. Thus, changes in a(i)(Na) modulate the increase in force due to increased Ca influx and control force development when Ca influx is either unchanged (low strophanthidin) or has reached a steady state (high [Ca](o), recovery from overdrive). Copyright 1994 S. Karger AG, Basel

Effects of the novel potassium channel opener, UR‐8225, on contractile responses in rat isolated smooth muscle

1. The effects of UR-8225 [(1,2-dihydro-4-(1,2-dihydro-2-oxo-1-pyridyl)-2,2-dimethyl-1-oxonapht halen-6- carbonitrile)] and levcromakalim were studied on the electrical and contractile responses induced by noradrenaline and KCl and on 86Rb+ efflux in rat aortic rings and on spontaneous mechanical activity in rat portal vein segments. 2. UR-8225 and levcromakalim, 10(-9) M-10(-5) M, relaxed the contractile responses induced by noradrenaline (IC50 = 2.7 +/- 0.4 x 10(-6) M and 6.6 +/- 1.3 x 10(-7) M, respectively) or 30 mM KCl (IC50 = 1.4 +/- 0.2 x 10(-7) M and 9.4 +/- 1.3 x 10(-8) M, respectively) more effectively than those induced by 80 mM KCl. The relaxant effect on noradrenaline-induced contractions was independent of the presence or absence of functional endothelium. 3. The vasorelaxant effect of UR-8225 and levcromakalim can be competitively antagonized by glibenclamide, an ATP-sensitive K+ channel blocker. There were no differences in the calculated pA2 values for glibenclamide to inhibit UR-8225- and levcromakalim-induced relaxations (7.61 +/- 0.08 and 7.69 +/- 0.10, respectively). The slope of the Schild plot yielded values not significantly different from unity (0.95 +/- 0.06 and 0.96 +/- 0.05, respectively). 4. UR-8225 (10(-5) M) hyperpolarized the resting aortic membrane potential from -50.7 +/- 0.7 mV to -66.0 +/- 2.0 mV and stimulated 86Rb+ efflux. 5. UR-8225 and levcromakalim inhibited the contractions induced by Ca2+ in aortae incubated in Ca(2+)-free PSS containing methoxyverapamil in the presence of noradrenaline. 6. Both drugs inhibited the amplitude of spontaneous activity in portal veins (IC50 = 5.1 +/- 1.4 x 10-8 M and 1.5 +/- 0.7 x 10-8 M, respectively), this effect being competitively antagonized by glibenclamide.7. These results indicated that UR-8225 exhibited qualitatively similar, but slightly less potent,vasorelaxant effects than those exerted by levcromakalim, which suggests that they can be related to its ability to activate ATP-sensitive K+ channels in vascular smooth muscle cells.

Differential neuromodulation of calcium currents by norepinephrine in rat sympathetic neurons.

1. Differences in the neuromodulation of Ca2+ currents between superior cervical ganglion (SCG) and more caudal paravertebral ganglion (PVG) neurons acutely isolated from the same rats were investigated using the whole-cell patch-clamp technique. 2. Norepinephrine (NE) induced a concentration-dependent inhibition of Ca2+ currents in both SCG and PVG neurons. The concentration producing 50% inhibition (IC50) for NE estimated from concentration-response curves was similar between SCG and PVG neurons but the maximal inhibition estimated from the concentration-response curve for PVG neurons was decreased compared with that of SCG neurons. 3. Tail current activation curves of both SCG and PVG neurons in the absence and presence of NE (5 microM) could be fitted to a double Boltzmann equation. In the presence of NE, the activation curves for both SCG and PVG neurons were shifted toward more depolarized potentials. The magnitude of the shift was greater in SCG than in PVG neurons, which could be accounted for by a greater decrease (P < 0.05) in the fractional amplitude of the first current component of SCG neurons (delta 1.4 +/- 0.4 nA, mean +/- SE, 39%) compared with that of PVG neurons (delta 0.9 +/- 0.1 nA, 16%). 4. Ca2+ current density, expressed as maximal tail current amplitude normalized to cell capacitance, was greater in PVG neurons than that in SCG neurons. 5. In SCG neurons, a saturating concentration of omega-conotoxin GVIA (omega-CgTx) produced a greater decrease of Ca2+ current amplitude at +20 mV (77.4 +/- 1.9%) than in PVG neurons (71.2 +/- 1.5%, P < 0.05). 6. After pretreatment with 15 microM omega-CgTx, NE still decreased the Ca2+ currents in both populations of neurons; however, the inhibition was greater in SCG neurons (31.1 +/- 3.4%) than in PVG neurons (12.8 +/- 3.6%, P < 0.01). 7. The dihydropyridine Ca2+ channel "agonist" Bay K 8644 (10 microM) prolonged Ca2+ tail currents in both SCG and PVG neurons. After normalizing to cell capacitance, there was no significant difference in Bay K 8644-induced tail current amplitude between the two populations of neurons. Moreover, NE (5 microM) increased the prolonged Ca2+ tail current amplitude induced by Bay K 8644 (10 microM) by 44.7 +/- 13.5% in SCG and 41.9 +/- 11.9% in PVG neurons. 8. Under control conditions, Ca2+ currents were facilitated by a depolarizing conditioning pulse (50 ms to +100 mV) in both PVG neurons (29.2 +/- 5.1%) and SCG neurons (20.1 +/- 4.0%).(ABSTRACT TRUNCATED AT 400 WORDS)

Reduced noradrenaline responsiveness of brown adipocytes isolated from estradiol-treated rats.

High plasma levels of estradiol are known to reduce the GDP binding of brown adipose tissue. Since GDP binding depends on the level of sympathetic discharge to brown adipose tissue, we measured the responsiveness to noradrenaline of brown adipocytes isolated from female rats with high plasma levels of estradiol. Noradrenaline responsiveness was assessed by measuring the respiration rate of isolated brown adipocytes in the presence of different concentrations of noradrenaline. Both control and treated adipocytes showed the same basal respiratory rate (27 +/- 6 and 24 +/- 4 nmol O2.min-1.10(-6) cells, respectively). The presence of noradrenaline (0.1, 1, and 10 microM) in the medium increased the respiration rate of both kinds of adipocytes in a dose-dependent manner. However, the response was markedly reduced in adipocytes isolated from estradiol-treated rats. These results suggest that estradiol impairs the responsiveness of brown adipose tissue to the sympathetic nervous system. Three possible mechanisms are suggested as accounting for the observed decreased responsiveness to noradrenaline, i.e., a direct action of estradiol in brown adipocytes, a modulatory role of estradiol in the central control of the sympathetic discharge to brown adipose tissue, and the interference of catecholestrogens with noradrenaline synthesis at the sympathetic terminals.

The black scorpion Heterometrus longimanus: Pharmacological and biochemical investigation of the venom

M. C. E. Gwee, P. T.-H. Wong, P. Gopalakrishnakone, L. S. Cheah and K. S. Y. Low. The black scorpion Heterometrus longimanus: pharmacological and biochemical investigation of the venom. Toxicon 31, 1305–1314, 1993.—Documentation on the biological activity (including the lethality) of the venom (BSV) from the black scorpion Heterometrus longimanus is lacking. We have investigated the effects of BSV on adrenergic transmission using the rat isolated anococcygeus muscle (Acm), since the venom from several species of scorpions causes peripheral sympathetic nerve stimulation with enhanced adrenergic responses. The catecholamine content in BSV was also measured by HPLC. The effects of phentolamine (5 μM), guanethidine (5 μM), desipramine (1.5 μM), tetrodotoxin (2 μM) and reserpine pretreatment in vivo (5 mg/ kg s. c. × 24 hr and 5 mg/ kg i. p. × 3 hr) on contractile responses of the rat Acm to field stimulation, crude BSV (2–10 μl in 6 ml bath), noradrenaline (3 μM), tyramine (10–15 μM), carbachol (2–3 μM) and potassium chloride (50–75 mM) were investigated. BSV mimicked the agonist actions of noradrenaline (NA) by acting directly on postjunctional α-adrenoceptors in the anococcygeus muscle. The ld 50 of crude BSV injected i.v. into mice was 0.13 ml per kg mouse. Sequential ultrafiltration of the crude BSV revealed the presence of a substance of low mol. wt which mediates the postjunctional α-agonist actions of BSV. HPLC measurements confirmed the presence of noradrenaline (NA; mean concentration of 1.8 ± 0.3 mM) in BSV; the dopamine concentration (mean of 31 ± 4 μM) was 60-fold lower than that of NA, whereas adrenaline was not detected in all the 15 samples investigated. Thus, the presence of NA in BSV can account for the postjunctional α-agonist actions of the venom in the Acm.

Changes in monoamine oxidase activity in mouse brain associated with d-methamphetamine dependence and withdrawal

The long-term effects of d-methamphetamine (MP, 5 mg/kg) on brain mitochondrial monoamine oxidase (MAO) activity were studied in mice given MP intraperitoneally daily for 4 weeks. The MAO activities decreased when serotonin (5-HT) and dopamine (DA) were used as substrates. A marked elevation in MAO activity was seen during MP withdrawal when 5-HT, DA, β-phenylethylamine (β-PEA) and norepinephrine (NE) were used as substrates. The kinetics of MAO showed a significant decrease in K m values, but no significant change in V max values during MP withdrawal, despite the presence of NE. The K m and V max values increased when NE was the substrate. Inhibition of MAO by MP or its metabolites (amphetamine, p-hydroxyamphetamine and p-hydroxymethamphetamine) increased with the use of the following substrates in the order: DA, 5-HT, NE and β-PEA.

Possible involvement of pertussis toxin‐sensitive GTP‐binding protein in the α2‐adrenoceptor‐mediated melanosome‐aggregation response of goldfish melanophores

AbstractThe signal‐transduction system involving α‐adrenoceptors, which controls the aggregation of melanosomes, was investigated in the melanophores of the black‐moor goldfish, Carassius auratus.The order of effectiveness of α‐subtype‐specific agonists and antagonists indicated that the major subtype of α‐adrenoceptor in these cells is α2. After a 12‐hr treatment, pertussis toxin markedly attenuated the melanosome‐aggregation response to norepinephrine (NE), but it failed to inhibit the Li+ ‐induced aggregation of melanosomes.Pertussis toxin catalyzed the [32P]‐ADP‐ribosylation of a 43‐kDa protein in a crude preparation of membranes from the goldfish melanophores. The radioactivity incorporation into the protein was much reduced by the presence of an analog of GTP, guanosine‐5′‐(3‐O‐thio)‐triphosphate, in the presence of NE. When the membranes were prepared from cells that had been pretreated with pertussis toxin, [32P]‐ADP‐ribosylation of the protein was not observed. These observations indicate that the 43‐kDa protein is the α subunit of a regulatory GTP‐binding protein, and that pertussis toxin inhibits the action of NE on the cells via ADP‐ribosylation of the protein.From these results, it is concluded that stimulation of α2‐adrenoceptors of goldfish melanophores induces the aggregation of melanosomes in a process mediated by a pertussis toxin‐sensitive GTP‐binding protein. © 1993 Wiley‐Liss, Inc.

Characterization of a Calcium‐dependent Current Generating a Slow Afterdepolarization of CA3 Pyramidal Cells in Rat Hippocampal Slice Cultures

A depolarization-induced, slowly decaying inward current was examined in slice-cultured CA3 pyramidal cells by voltage-clamp techniques and microfluorometric measurements of cytosolic free Ca2+ concentration ([Ca2+]i). Action potentials elicited by intracellular injection of short-lasting (50-100 ms) depolarizing current pulses were followed by a slowly decaying afterhyperpolarization (AHP). After switching to voltage-clamp mode, short-lasting (50-100 ms) depolarizing voltage jumps from -60 mV to between -30 and 0 mV induced a slowly decaying outward aftercurrent (IAHP) which was depressed by bath application of muscarine (0.5 microM). In the presence of muscarine, the same depolarizations induced a slowly decaying afterdepolarization (ADP) or inward aftercurrent (IADP) in voltage-clamp mode. This current was also induced in the presence of trans(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD, 5 microM), an agonist of metabotropic glutamate receptors, but not in the presence of noradrenalin (5 microM), while both of these agonists depressed IAHP. IADP was depressed by reducing the external Ca2+ concentration from 3.8 to 0.5 mM, by external Co2+ (1 mM) and by external Cd2+ (10-100 microM). Combined voltage-clamp recordings and microfluorometric measurements of [Ca2+]i using the Ca2+ indicator fura-2 revealed that the amplitude of IADP was correlated with the amplitude of depolarization-induced Ca2+ influx. IADP was absent at membrane potentials < -90 mV, and reached maximal amplitudes at approximately -55 mV. Raising the extracellular K+ concentration from 2.7 to 13.5 mM increased the amplitude of IADP and resulted in a positively directed shift of the apparent reversal potential of IADP. When the external Na+ concentration was reduced from 157 to 33 or 18 mM the current reversed at more negative potentials and was reduced to 40 and 21%, respectively, of control amplitude. Lowering the external CI- concentration from 159 to 20 mM did not affect IADP. We conclude that IADP most likely represents a Ca(2+)-activated cation current, rather than a Ca2+ tail current, or an electrogenic Ca2+ extrusion current.

MECHANISMS OF TENSION DEVELOPMENT INDUCED BY MONENSIN IN GUINEA-PIG AORTA : EFFECTS OF VERAPAMIL, OUABAIN, PRAZOSIN AND GLIBENCLAMIDE

The influence of monensin (10 µmol/L) alone and in the presence of verapamil (3 µmol/L) or ouabain (1 mmol) and prazosin (1 µmol/L) or glibenclamide (10 µmol/L) were studied on the muscle tension of guinea pig aorta. Changes in tissue sodium, potassium and calcium ion contents of the aortic muscle produced by monensin in the presence of prazosin were evaluated. Monensin in normal Tyrode's solution containing prazosin caused an increase in the resting tension followed by a decrease and returned to normal values. Verapamil reduced the muscle tension induced by monensin. After ouabain, monensin induced sustained increase in the resting tension. Glibenclamide partially reversed the relaxant phase of monensin in presence of norepinephrine. The findings of the present study indicate that the contraction induced by monensin in guinea Pig aorta is due to the increased influx of calcium through voltage-dependent calcium Channels as well as through Na+ - Ca2+ exchange mechanisms. Monensin produced relaxation of guinea pig aorta in part through the increase in K+ permeability via opening of K+-ATP channels.