Mechanisms involved in morphine-induced activation of synaptosomal Na+,K+-ATPase

Ultralow concentrations of bupivacaine exert anti-inflammatory effects on inflammation-reactive astrocytes

Bupivacaine is a widely used, local anesthetic agent that blocks voltage-gated Na(+) channels when used for neuro-axial blockades. Much lower concentrations of bupivacaine than in normal clinical use, < 10(-8)  m, evoked Ca(2+) transients in astrocytes from rat cerebral cortex, that were inositol trisphosphate receptor-dependent. We investigated whether bupivacaine exerts an influence on the Ca(2+) signaling and interleukin-1β (IL-1β) secretion in inflammation-reactive astrocytes when used at ultralow concentrations, < 10(-8)  m. Furthermore, we wanted to determine if bupivacaine interacts with the opioid-, 5-hydroxytryptamine- (5-HT) and glutamate-receptor systems. With respect to the μ-opioid- and 5-HT-receptor systems, bupivacaine restored the inflammation-reactive astrocytes to their normal non-inflammatory levels. With respect to the glutamate-receptor system, bupivacaine, in combination with an ultralow concentration of the μ-opioid receptor antagonist naloxone and μ-opioid receptor agonists, restored the inflammation-reactive astrocytes to their normal non-inflammatory levels. Ultralow concentrations of bupivacaine attenuated the inflammation-induced upregulation of IL-1β secretion. The results indicate that bupivacaine interacts with the opioid-, 5-HT- and glutamate-receptor systems by affecting Ca(2+) signaling and IL-1β release in inflammation-reactive astrocytes. These results suggest that bupivacaine may be used at ultralow concentrations as an anti-inflammatory drug, either alone or in combination with opioid agonists and ultralow concentrations of an opioid antagonist.

Naloxone in ultralow concentration restores endomorphin-1-evoked Ca²⁺ signaling in lipopolysaccharide pretreated astrocytes

Long-term pain is a disabling condition that affects thousands of people. Pain may be sustained for a long time even after the physiological trigger has resolved. Possible mechanisms for this phenomenon include low-grade inflammation in the CNS. Astrocytes respond to inflammatory stimuli and may play an important role as modulators of the inflammatory response in the nervous system. This study aimed first to assess how astrocytes in a primary culture behave when exposed to the endogenous μ-opioid receptor agonist endomorphin-1 (EM-1), in a concentration-dependent manner, concerning intracellular Ca²⁺ responses. EM-1 stimulated the μ-opioid receptor from 10⁻¹⁵ M up to 10⁻⁴ M with increasing intensity, usually reflected as one peak at low concentrations and two peaks at higher concentrations. Naloxone, pertussis toxin (PTX), or the μ-opioid receptor antagonists CTOP did not totally block the EM-1-evoked Ca²⁺ responses. However, a combination of ultralow concentration naloxone (10⁻¹² M) and PTX (100 ng/ml) totally blocked the EM-1-evoked Ca²⁺ responses. This suggests that ultralow (picomolar) concentrations of naloxone should block the μ-opioid receptor coupled G(s) protein, and that PTX should block the μ-opioid receptor coupled G(i/o) protein. The second aim was to investigate exposure of astrocytes with the inflammatory agent lipopolysaccharide (LPS). After 4 h of LPS incubation, the EM-1-evoked Ca²⁺ transients were attenuated, and after 24 h of LPS incubation, the EM-1-evoked Ca²⁺ transients were oscillated. To restore the EM-1-evoked Ca²⁺ transients, naloxone was assessed as a proposed anti-inflammatory substance. In ultralow picomolar concentration, naloxone demonstrated the ability to restore the Ca²⁺ transients.

Oxidative stress induced by morphine in brain of rats fed with a protein deficient diet

The objective of the study is to determine the damage by oxidative stress induced by morphine in brain of rats fed with a protein-deficient diet. Twenty-eight malnourished male Wistar rats, 30 days old, were used in the study. The animals were divided into four groups of 7 rats per group. Group I received NaCl and the groups II; III and IV intraperitoneally received 3, 6 and 12 mg/kg of morphine sulphate, respectively, in a single dose. Animals were sacrificed and the levels of glutathione (GSH), dopamine, tryptophan and 5-hydroxyindole-3-acetic acid (5-HIAA) as well as, Na(+)/K(+) ATPase and total ATPase activity in the brain were measured. Tryptophan levels and Na(+)/K( +) ATPase activity showed non-significant changes in the experimental group. Levels of 5-HIAA decreased significantly (p = .03) in animals that received 12 mg/kg of morphine and in animals that received 3 mg/kg, levels of GSH and dopamine were found to have a significant decrease (p < .05), but a significant increase in the group that received 12 mg/kg of morphine (p < .05). Total ATPase activity increased significantly in the groups that received 3 mg/kg (p = .015) and 6 mg/kg (p = .0001) of morphine. The results show that malnutrition induces changes in cellular regulation and biochemical responses to oxidative stress caused by morphine sulphate.

Role of cannabinoid CB1 receptors and Gi/o protein activation in the modulation of synaptosomal Na+,K+-ATPase activity by WIN55,212-2 and delta(9)-THC

In the present study, we evaluated the effects of the synthetic cannabinoid receptor agonist (R)-(+)-[2,3-Dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN55,212-2) and the active component of Cannabis delta-9-tetrahydrocannabinol (triangle up(9)-THC) on Na(+),K(+)-ATPase activity in synaptosomal mice brain preparation. Additionally, the potential exogenous cannabinoids and endogenous opioid peptides interaction as well as the role of G(i/o) proteins in mediating Na(+),K(+)-ATPase activation were also explored. The ouabain-sensitive Na(+),K(+)-ATPase activity was measured in whole-brain pure intact synaptosomes (obtained by Percoll gradient method) of female CF-1 mice and was calculated as the difference between the total and the ouabain (1 mM)-insensitive Na(+),K(+)-ATPase activities. Incubation in vitro of the synaptosomes with WIN55,212-2 (0.1 pM-10 microM) or triangle up(9)-THC (0.1 pM-0.1 microM), in a concentration-dependent manner, stimulated ouabain-sensitive Na(+),K(+)-ATPase activity. WIN55,212-2 was less potent but more efficacious than triangle up(9)-THC. N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM-251) (10 nM), a CB(1) cannabinoid receptor selective antagonist, had not effect per se but antagonized the enhancement of Na(+),K(+)-ATPase activity induced by both, WIN55,212-2 and triangle up(9)-THC. AM-251 produced a significant reduction in the E(max) of cannabinoid-induced increase in Na(+),K(+)-ATPase activity, but did not significantly modify their EC(50). On the other hand, co-incubation with naloxone (1 microM), an opioid receptor antagonist, did not significantly modify the effect of WIN55,212-2 and completely failed to modify the effect of triangle up(9)-THC on synaptosomal Na(+),K(+)-ATPase. Finally, pre-incubation with 0.5 microg of pertussis toxin (G(i/o) protein blocker) completely abolished the enhancement of ouabain-sensitive Na(+),K(+)-ATPase activity induced by WIN55,212-2. A lower dose, 0.25 microg, decreased the E(max) of WIN55,212-2 by 70% but did not significantly affect its EC(50). These results suggest that WIN55212-2 and triangle up(9)-THC indirectly enhance Na(+),K(+)-ATPase activity in the brain by activating cannabinoid CB(1) receptors in a naloxone-insensitive manner. In addition, the effect of WIN55,212-2 on neuronal Na(+),K(+)-ATPase is apparently due to activation of G(i/o) proteins.

Involvement of dopamine system in regulation of Na+,K+-ATPase in the striatum upon activation of opioid receptors by morphine

The striatum is believed to be a crucial brain region associated with drug reward. Adaptive alteration of neurochemistry in this area might be one potential mechanism underlying drug dependence. It has been proposed that the dysfunction of Na+,K+-ATPase function is involved in morphine tolerance and dependence. The present study, therefore, was undertaken to study the adaptation of the striatal Na+,K+-ATPase activity in response to morphine treatment. The results demonstrated that in vivo short-term morphine treatment stimulated Na+,K+-ATPase activity in a dose-dependent manner. This action could be significantly inhibited by D2-like dopamine receptor antagonist S(-)-3-chloro-5-ethyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-hydroxy-2-methoxybenzamine (eticlopride). Contrary to shortterm morphine treatment, long-term morphine treatment significantly suppressed Na+,K+-ATPase activity. This effect could be significantly inhibited by D(1)-like dopamine receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390). However, both short-term and long-term morphine treatment-induced changes in Na+,K+-ATPase activity could be reversed by opioid receptor antagonist naltrexone. It was further found that cAMP-dependent protein kinase (PKA) was crucially involved in regulating Na+,K+-ATPase activity by morphine. Different regulation of the phosphorylation levels of the alpha3 subunit of Na+,K+-ATPase by PKA was related to the distinct modulations of Na+,K+-ATPase by short-term and long-term morphine treatment. Short-term morphine treatment inhibited PKA activity and then decreased the phosphorylation of Na+,K+-ATPase, leading to increase in enzyme activity. These effects were sensitive to eticlopride or naltrexone. Conversely, long-term morphine treatment stimulated PKA activity and then increased the phosphorylation of Na+,K+-ATPase, leading to the reduction of enzyme activity. These effects were sensitive to SCH 23390 or naltrexone. These findings demonstrate that dopamine receptors are involved in regulation of Na+,K+-ATPase activity after activation of opioid receptors by morphine.

Assessment of Oxidative Damage Induced by Acute Doses of Morphine Sulfate in Postnatal and Adult Rat Brain

The aim of the present study is to evaluate the oxidative damage in rats of different ages. Weaned rats of 25 g and adults of 300 g were used in groups of 6, a single i.p. dose of morphine sulfate of 3, 6 or 12 mg/kg was administered. All animals were sacrificed to measure GSH and 5-HT levels in brain by liquid chromatography, as well as Na(+), K(+)-ATPase and total ATPase enzymatic activity. 5-HT levels decreased significantly (p < 0.05) in adult animals that received 3 and 6 mg morphine. Na(+), K(+)-ATPase activity increased significantly (p < 0.05) in all groups of weaned animals. In adult animals, Na(+), K(+)-ATPase and total ATPase partially diminished. GSH levels diminished significantly (p < 0.05) both in weaned and in adult groups. The results indicate age-induced changes in cellular regulation and biochemical responses to oxidative stress induced by morphine.

Modulation of Na, K-ATPase activity by prostaglandin E1 and [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin

Adenylyl cyclase is activated by prostaglandin E and inhibited by mu-opioids. Since cAMP-related events influence the activity of the Na Pump and its biochemical correlate Na,K-ATPase in many systems, we tested the hypothesis that prostaglandin E1 and [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO), a mu-opioid agonist, have opposing actions on Na,K-ATPase activity. Studies were conducted with alamethicin-permeabilized SH-SY5Y human neuroblastoma cells. Prostaglandin E1 (1 microM) transiently inhibited Na,K-ATPase activity for 10-15 min. A direct activator of protein kinase A, 8-Br-cAMP (150 and 500 microM), also inhibited, but more rapidly and for a shorter duration. Both DAMGO (1 microM) and Rp-adenosine 3',5'-cyclic monophosphorothioate (500 microM), a protein kinase A-inhibitor, reversed the inhibitory effect of prostaglandin E1. DAMGO alone (1 microM) stimulated Na,K-ATPase activity up to nearly three-fold control activity. The stimulatory action of DAMGO was blocked by cyclosporine A (2 microM), an inhibitor of calcineurin, and was dependent on Ca2+ entry through nifedipine-sensitive Ca2+ channels. In the presence of 1 mM EGTA, DAMGO inhibited Na,K-ATPase activity. DAMGO-induced inhibition was blocked by the inositol 1,4,5-trisphosphate receptor antagonist xestospongin C (1 microM). Na,K-ATPase is poised to modulate neuronal excitability through its roles in maintaining the membrane potential and transmembrane ion gradients. The differential effects of prostaglandin E1 and opioids on Na,K-ATPase activity may be related to their actions in hyperalgesia.

Involvement of cAMP/cAMP-dependent protein kinase signaling pathway in regulation of Na+,K+-ATPase upon activation of opioid receptors by morphine

The depolarization of neurons induced by impairment of Na+,K+-ATPase activity after long-term opiate treatment has been shown to involve the development of opioid dependence. However, the mechanisms underlying changes in Na+,K+-ATPase activity after opioid treatment are unclear. The best-established molecular adaptation to long-term opioid exposure is up-regulation of the cAMP/cAMP-dependent protein kinase (PKA) signaling pathway; this study, therefore, was undertaken to investigate the role of up-regulation of cAMP/PKA signaling pathway in alteration of the mouse hippocampal Na+,K+-ATPase activity. The results demonstrated that short-term morphine treatment dose dependently stimulated Na+,K+-ATPase activity. This action could be significantly suppressed by adenylyl cyclase activator 7beta-acetoxy-8,13-epoxy-1alpha,6beta,9alpha-trihydroxylabd-14-en-11-one (forskolin), or the cAMP analog dibutyryl-cAMP. Contrary to short-term morphine treatment, long-term treatment significantly inhibited Na+,K+-ATPase activity. Moreover, an additional decrease in Na+,K+-ATPase activity was observed by naloxone precipitation. The effects of both short- and long-term morphine treatment on Na+,K+-ATPase activity were naltrexone-reversible. The regulation of Na+,K+-ATPase activity by morphine was inversely correlated with intracellular cAMP accumulation. N-[2-(4-Bromocinnamylamino)ethyl]-5-isoquinoline (H89), a specific PKA inhibitor, mimicked the stimulatory effect of short-term morphine but antagonized the inhibitory effect of long-term morphine treatment on Na+,K+-ATPase activity. However, okadaic acid, a protein phosphatase inhibitor, suppressed short-term morphine stimulation but potentiated long-term morphine inhibition of Na+,K+-ATPase activity. The regulation of Na+,K+-ATPase activity by morphine treatment seemed to associate with the alteration in phosphorylation level but not to be relevant to the change in abundance of Na+,K+-ATPase. These findings strongly demonstrate that cAMP/PKA signaling pathway involves regulation of Na+,K+-ATPase activity after activation of opioid receptors.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Role of Na(+), K(+)-ATPase in morphine-induced antinociception

We evaluated the modulation by Na+,K+-ATPase inhibitors of morphine-induced antinociception in the tail-flick test and [3H]naloxone binding to forebrain membranes. The antinociception induced by morphine (1-32 mg/kg, s.c.) in mice was dose-dependently antagonized by ouabain (1-10 ng/mouse, i.c.v.), which produced a significant shift to the right of the morphine dose-response curve. The i.c.v. administration of three Na+,K+-ATPase inhibitors (ouabain at 0.1-100, digoxin at 1-1000, and digitoxin at 10-10000 ng/mouse) dose-dependently antagonized the antinociceptive effect of morphine (4 mg/kg, s.c.) in mice, with the following order of potency: ouabain > digoxin > digitoxin. This effect cannot be explained by any interaction at opioid receptors, since none of these Na+,K+-ATPase inhibitors displaced [3H]naloxone from its binding sites, whereas naloxone did so in a concentration-dependent manner. The antinociception induced by morphine (5 mg/kg, s.c.) in rats was antagonized by the i.c.v. administration of ouabain at 10 ng/rat, whereas it was not significantly modified by intrathecally administered ouabain (10 and 100 ng/rat). These results suggest that the activation of Na+,K+-ATPase plays a role in the supraspinal, but not spinal, antinociceptive effect of morphine.

Evaluation of endomorphin-1 on the activity of Na(+),K(+)-ATPase using in vitro and in vivo studies

The goal of this study was to investigate the effects of endomorphin-1 on Na(+),K(+)-ATPase activity in mouse brain synaptosome in vitro, and its antinociceptive interaction with the Na(+),K(+)-ATPase inhibitor ouabain. Endomorphin-1 (0.1 nM-10 microM) produced a concentration-dependent (EC(50): 43.19 nM, CI: 23.38-65.71 nM, E(max): 25.86%, CI: 24.53-27.20%), naloxone-reversible increase of the synaptosomal Na(+),K(+)-ATPase activity. The intrathecally (i.t.) administered endomorphin-1 (2-20 microg) produced a dose-dependent short-lasting increase in the tail-flick latency. Ouabain itself (1-1000 ng, i.t.) did not cause antinociception. Treatment with 10 ng ouabain significantly decreased the antinociceptive effect of 2 microg endomorphin-1, but none of the other combinations did significantly differ from the endomorhin-1-treated groups. These data indicate that endomorphin-1 increases the activity of Na(+),K(+)-ATPase in vitro but this effect may play a weak role in the antinociception induced by intrathecal endomorphin-1.