Adenosine but not an adenine nucleotide mediates tonic purinergic inhibition, as well as inhibition by glutamate, of noradrenaline release in rabbit brain cortex slices

Activation of cholinergic and adrenergic receptors increases the concentration of extracellular adenosine in the cerebral cortex of unanesthetized rat

Adenosine is an inhibitory neuromodulator in the CNS. For extracellular adenosine to play a physiological role in the brain, it must be present at effective concentrations. Acetylcholine and noradrenaline are known to play an important role in modulating the activity of cortical neurons, and they might have a role also in the release of adenosine in the cerebral cortex in vivo. We examined whether activation of cholinergic and adrenergic receptors affects extracellular adenosine levels in the cerebral cortex of unanesthetized rats using in vivo microdialysis. All drugs were administered locally within the cortex by reverse dialysis. Both acetylcholine and the acetylcholinesterase inhibitor neostigmine increased extracellular adenosine levels, and the effect of neostigmine was blocked by the nicotinic receptor antagonist mecamylamine. Both nicotine and the nicotinic receptor agonist epibatidine increased the concentration of extracellular adenosine. Activation of muscarinic receptors using the nonselective agonist oxotremorine and a selective M1 receptor agonist also increased extracellular adenosine levels. Noradrenaline and the noradrenergic reuptake inhibitor desipramine increased extracellular adenosine levels. The alpha(1)-adrenergic receptor agonist phenylephrine and the beta-adrenergic agonist isoproterenol increased extracellular adenosine levels, whereas the alpha(2)-adrenergic receptor agonist clonidine did not have an effect. These findings indicate that activation of specific cholinergic and adrenergic receptors can increase extracellular levels of adenosine in the cortex, and suggest that cholinergic and adrenergic receptor-mediated regulation of adenosine levels may represent a mechanism for controlling the excitability of cortical neurons.

Activation of presynaptic A1-receptors by endogenous adenosine inhibits acetylcholine release in the guinea-pig ileum

1. It is well established that presynaptic adenosine A1-receptor activation inhibits acetylcholine (ACh) release in the guinea-pig ileum. The present study extends this observation and examines a possible role for endogenous adenosine in modulating cholinergic nerve function. 2. The actions of the adenosine uptake blocker, dipyridamole, the adenosine deaminase inhibitor, erythro-9(2-hydroxy-3-nonyl)adenine (EHNA) and the A1-receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) were examined on electrically evoked neurogenic, cholinergic twitch contractions of the guinea-pig ileum. Some additional studies measuring [3H]-ACh release were also performed. 3. Adenosine and the selective A1-receptor agonist, 2-chloroadenosine (2-CA), inhibited electrically evoked contractions and, in the case of 2-CA, [3H]-ACh release. The actions were antagonized by DPCPX. At low concentrations, dipyridamole and EHNA enhanced the effect of adenosine causing a leftward shift of the concentration-response curve. In contrast, inhibition induced by 2-CA was unaffected by either dipyridamole or EHNA. 4. When applied alone at higher concentrations, EHNA and dipyridamole produced a concentration-dependent suppression of cholinergic neurotransmission. In both cases, the effect could be reversed by DPCPX. At the same concentration, DPCPX alone produced a small but consistent increase in twitch height and [3H]-ACh release. 5. The data confirm the existence of inhibitory presynaptic adenosine A1-receptors modulating cholinergic nerve function in the guinea-pig ileum and suggests that these receptors can be activated by endogenous adenosine released either as adenosine itself or as an ATP metabolite.

Effect of aging on A1-adenosine receptor-mediated inhibition of norepinephrine release in the rat heart

Adenosine inhibits norepinephrine (NE) release from cardiac adrenergic nerves and reduces the postsynaptic beta-adrenergic mediated actions of NE, leading to decreased myocardial force of contraction. The actions of adenosine are mediated by pre- and postsynaptic adenosine A1 receptors (A1-AdoR). We reported that adenosine inhibition of postsynaptic beta-adrenergic receptor-mediated cyclic adenosine monophosphate (cAMP) production declines with age in male F344 rat hearts. In this study, cardiac synaptosomes, isolated intact adrenergic nerve terminals, were used to examine the effect of age on adenosine inhibition of NE release. Cardiac synaptosomes were prepared from the hearts of 6- and 24-month-old male F344 rats, loaded with [3H]NE, and placed in a superfusion system. [3H]NE release was induced by high [K+] exposure in the presence of varying concentrations of adenosine or the specific A1-AdoR agonist, N6-p-sulfophenyladenosine (SPA). [3H]NE release was significantly reduced in old rats compared with young rats. Inhibition of [3H]NE release by adenosine and SPA was significantly greater in young rats compared with old rats. The A1-AdoR antagonist, 8-(p-sulfophenyl)-theophylline, blocked the actions of adenosine on [3H]NE release, and the specific adenosine A2-receptor agonist, cyclopropylcarboxamidoadenosine, had no effect on [3H]NE release. Our data suggest that presynaptic A1-AdoR-mediated inhibition of NE release in the rat heart declines with age.

Release of ATP from cultured rat astrocytes elicited by glutamate receptor activation

The release of ATP was studied in cultures of astrocytes derived from the brain hemispheres of newborn rats. There was a basal efflux of ATP, which was increased up to 19-fold by glutamate (300-1000 microM). N-methyl-D-aspartate (20-500 microM), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA; 30-100 microM) and kainate (20 microM). The N-methyl-D-aspartate receptor-selective antagonist 2-amino-5-phosphonopentanoate (100 microM) blocked the effect of N-methyl-D-aspartate but not the effects of AMPA, kainate and glutamate. The AMPA receptor-selective antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (30 microM) blocked the effect of AMPA and also of glutamate and N-methyl-D-aspartate, but not the effect of kainate. The kainate receptor-selective antagonist D-glutamyl-amino-methanesulfonate (30 microM) blocked the effect of kainate but not of glutamate. Glutamate (1000 microM) did not increase the release of lactate dehydrogenase from astrocytes. Excitatory amino acids are known to release adenyl compounds in the brain. The present results identify one adenyl compound thus released, namely ATP, and identify astrocytes as one source. The release is brought about by activation of any of the three ionotropic glutamate receptor types-N-methyl-D-aspartate, AMPA and kainate receptors. AMPA receptors seem to mediate at least a part of the effect of glutamate itself, but the involvement of other receptors cannot be ruled out. ATP and its degradation products, such as adenosine, once released, may exert acute as well as trophic effects on neurons and glial cells.

Presynaptic modulation by L-glutamate and GABA of sympathetic co-transmission in rat isolated vas deferens

1. The modulatory effects of L-glutamate and its structural analogues, and of gamma-aminobutyric acid (GABA), on sympathetic co-transmission were studied in the rat isolated vas deferens exposed to electrical field stimulation (EFS). 2. Application of exogenous L-glutamate caused a concentration-dependent (1 microM-3 mM) inhibition of the rapid twitch component of the biphasic EFS contraction. However, L-glutamate (1 microM-3 mM) had a minimal effect on the phasic contraction induced by exogenous adenosine 5'-triphosphate (ATP, 150 microM) and noradrenaline (50 microM). Unlike L-glutamate, D-glutamate had no effect on the EFS contraction. 3. The L-glutamate-induced inhibition of the EFS contractions was significantly attenuated by the glutamate decarboxylase (GAD) inhibitor 3-mercapto-propionic acid (150 microM) and was abolished in the presence of the GABA transaminase (GABA-T) inhibitor, 2-aminoethyl hydrogen sulphate (500 microM). 4. The L-glutamate-induced inhibition of the electrically evoked contraction was not affected by the adenosine A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)(30 nM), reactive blue 2 (30 microM) or the GABAA receptor antagonist bicuculline (50 microM). However, the GABAB receptor antagonist 2-hydroxysaclofen (50 microM) significantly inhibited the L-glutamate effect. 5. Similar to L-glutamate, GABA also caused a concentration-dependent (0.1-100 microM) inhibition of the EFS contractions. This GABA-induced inhibition was not affected by either the GABAA receptor antagonist bicuculline (50 microM) or reactive blue 2 (30 microM). However, a significant attenuation of the GABA-mediated effect was recorded with the GABAB receptor antagonist 2-hydroxysaclofen (50 microM). Contractions of the vas deferens induced by exogenous ATP and noradrenaline were not affected by GABA (0.1-100 microM). 6. The L-glutamate analogues, N-methyl-D-aspartate (NMDA) (1 microM-1 mM) and quisqualate (Quis 0.1 microM-0.3 mM) had no effect, whilst kainate (Kain, 1 microM-1 mM) caused an inhibition of the EFS-induced contractions. Effects of Kain could be abolished by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dioxine (CNQX, 10 microM). NMDA, Quis and Kain had no effect on the exogenous ATP- or noradrenaline-induced contractions. 7. It is concluded that the excitatory amino acid L-glutamate modulates the electrically evoked vas deferens contraction through conversion to the inhibitory amino acid GABA by a specific GABA transaminase. The GABA formed may then act on GABAB receptors and cause inhibition of the contraction through a presynaptic mechanism.

Evidence for P2-purinoceptor-mediated inhibition of noradrenaline release in rat brain cortex

1. Some postganglionic sympathetic axons possess P2Y-like P2-purinoceptors which, when activated, decrease the release of noradrenaline. We examined the question of whether such receptors also occur at the noradrenergic axons in the rat brain cortex. Slices of the brain cortex were preincubated with [3H]-noradrenaline, then superfused with medium containing desipramine (1 microM) and stimulated electrically, in most experiments by trains of 4 pulses/100 Hz. 2. The selective adenosine A1-receptor agonist, N6-cyclopentyl-adenosine (CPA; 0.03-3 microM) as well as the non-subtype-selective agonist 5'-N-ethylcarboxamido-adenosine (NECA; 0.3-3 microM) reduced the evoked overflow of tritium, whereas the adenosine A2a-receptor agonist, 2-p-(2-carbonylethyl)-phenethylamino-5'-N-ethylcarboxamido-a denosine (CGS-21680; 0.003-30 microM) and the adenosine A3-receptor agonist N6-2-(4-aminophenyl)ethyl-adenosine (APNEA; 0.03-3 microM) caused no change. Of the nucleotides tested, ATP (30-300 microM), adenosine-5'-O-(3-thiotriphosphate) (ATP gamma S; 30-300 microM), adenosine-5'-O-(2-thiodiphosphate) (ADP beta S; 30-300 microM), P1,P4-di(adenosine-5')-tetraphosphate (Ap4A; 30-300 microM) and the preferential P2Y-purinoceptor agonist, 2-methylthio-ATP (300 microM) decreased the evoked overflow of tritium. The P2X-purinoceptor agonist, alpha,beta-methylene-ATP (3-300 microM) caused no change. 3. The A1-selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 10 nM) attenuated the effects of the nucleosides CPA (apparent pKB value 9.8) and NECA as well as of the nucleotides ATP (apparent pKB 9.3), ATP gamma S (apparent pKB 9.2) and ADP beta S (apparent pKB 8.7). CGS-21680 and APNEA were ineffective also in the presence of DPCPX. The A2-selective antagonist 1,3-dipropyl-8-(3,4-dimethoxystyryl)-7-methylxanthine (KF-17837) reduced the effects of CPA, NECA and ATP gamma S only when given at a concentration of 300 nM but not at 1O nM.4. The P2-purinoceptor antagonists, suramin (300 micro M), reactive blue 2 (30 micro M) and cibacron blue 3GA(30 micro M) did not change the effect of CPA. Suramin and cibacron blue 3GA shifted the concentration response curve of ATP gamma S to the right (apparent pKB values 3.7 and 5.0, respectively). Reactive blue 2 also attenuated the effect of ATPyS, and cibacron blue 3GA attenuated the effect of ATP, but in these cases the agonist concentration-response curves were not shifted to the right. There was no antagonistic effect of suramin against ATP and ADP beta S.5. The results indicate that rat cerebrocortical noradrenergic axons possess, in addition to the knownadenosine Al-receptor, a separate purinoceptor for nucleotides (P2) which, in contrast to the Al-receptor,is blocked by suramin, reactive blue 2 and cibacron blue 3GA. Nucleotides such as ATP and ATP gamma S activate both receptors. Inconsistencies in antagonist effects against nucleotides are probably due to this activation of two receptors. The presynaptic P2-purinoceptor is P2Y-like, as it is in the peripheral sympathetic nervous system.

Effects of L-glutamate on the responses to nerve stimulation in rat isolated atria

In rat atria isolated with their sympathetic fibres the chronotropic responses to nerve stimulation with pulses of 2 ms duration were reduced in a concentration-dependent manner by 10 microM to 1 mM L-glutamate (Glu) and by 0.01 to 1.00 microM (R,S)-3-hydroxy-5-methoxyloxasole-4-propionic acid (AMPA), whereas they were unaffected by other agonists of Glu receptors such as 1 microM to 1 mM N-methyl-D-aspartic acid (NMDA), 10 microM to 1 mM kainate and 1 to 100 microM (+/-)-2-amino-4-phosphonobutyric acid (AP4). The reductions in the atrial responses to nerve stimulation caused by Glu were not accompanied by alterations in either the basal efflux of [3H]noradrenaline or its overflow in response to the stimulation. The sensitivity of the atria to exogenous noradrenaline was not modified by either Glu or AMPA. The decreases in the chronotropic responses caused by Glu and by AMPA were prevented by both the non-selective Glu receptor antagonist, 100 microM kynurenic acid, and the selective AMPA receptor antagonist, 10 to 50 microM 6,7-dinitroquinoxaline-2,3-dione (DNQX). In addition, the adenosine receptor antagonist, 8-phenyltheophylline (10 microM), as well as the muscarinic acetylcholine receptor antagonist, atropine (3 microM), prevented the inhibitory effects of both Glu and AMPA on the chronotropic responses of rat isolated atria. Since both adenosine and acetylcholine are known to exert negative inotropic and chronotropic effects in cardiac tissues, it is proposed that Glu could contribute, through the interaction with receptors of the AMPA type, to facilitate the release of adenosine and acetylcholine from the atria.(ABSTRACT TRUNCATED AT 250 WORDS)

Presynaptic modulation of the release of the co-transmitters noradrenaline and ATP

The release of both sympathetic co-transmitters, noradrenaline and ATP, is modulated via presynaptic receptors. However, the degree of the modulation may differ indicating that the ratio of the released co-transmitters changes upon presynaptic receptor activation. For example, alpha 2-autoinhibition affects the release of noradrenaline more markedly than the release of ATP. Some sympathetic axon terminals possess presynaptic P2-purinoceptors which are activated by endogenous ATP. These receptors are a novel kind of auto-receptor: they mediate a presynaptic negative feedback mechanism in which released ATP inhibits subsequent co-transmitter release.

Purinergic modulation of the evoked release of [3H]acetylcholine from the hippocampus and cerebral cortex of the rat: role of the ectonucleotidases

Modulation by exogenous and endogenous adenine nucleotides and adenosine of [3H]acetylcholine release evoked by veratridine (10 microM) was compared in synaptosomal fractions from the hippocampus and the cerebral cortex of the rat. In both brain areas, exogenously added ATP or adenosine (10-100 microM) inhibited the evoked tritium release. In the hippocampus, ATP gamma S, an ATP analogue more resistant to catabolism than ATP, was virtually devoid of effect on tritium release, and the effect of ATP was prevented by the ecto-5'-nucleotidase inhibitor alpha,beta-methylene ADP (100 microM), by adenosine deaminase (2 U/ml) and by the A1 adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 20 nM). In contrast, in the cerebral cortex, the effect of ATP on tritium release was not prevented by either alpha,beta-methylene ADP (100 microM) or adenosine deaminase (2 U/ml), and several ATP analogues (30 microM) inhibited release. The order of intensity of the inhibitory effects of the ATP analogues was: ATP gamma S > ATP > beta,gamma-imido ATP > beta,gamma-methylene ATP >> 2-methyl-S-ATP, alpha,beta-methylene ATP. The effect of ATP gamma S in the cerebral cortex was prevented by DPCPX (20 nM) and was not affected by the P2 purinoceptor antagonist suramin (100 microM). In the hippocampus, alpha,beta-methylene ADP (100 microM) increased the evoked release of tritium, and adenosine deaminase (2 U/ml) produced an even greater increase; when adenosine deaminase was added in the presence of alpha,beta-methylene ADP, adenosine deaminase still increased the evoked release of tritium. In the cerebral cortex, DPCPX (20 nM) and adenosine deaminase (2 U/ml) increased the evoked tritium release by a similar magnitude, but the effect of adenosine deaminase was smaller than in the hippocampus. It is concluded that in the cerebral cortex ATP as such presynaptically inhibits acetylcholine release, whereas in the hippocampus the role of adenine nucleotides is as a source of endogenous extracellular adenosine that tonically inhibits acetylcholine release. The results also show that besides formation of adenosine from adenine nucleotides, released adenosine as such contributes in nearly equal amounts to the pool of endogenous adenosine that presynaptically inhibits acetylcholine release in the hippocampus.

Ionotropic glutamate receptor types leading to adenosine-mediated inhibition of electrically evoked [3H]-noradrenaline release in rabbit brain cortex slices

1. Glutamate inhibits the electrically evoked release of noradrenaline in rabbit brain cortex slices; the inhibition is mediated by adenyl compounds, presumably adenosine. The aim of the present study was to identify the receptors involved in this indirect inhibitory effect of glutamate. Slices of the occipitoparietal cortex were preincubated with [3H]-noradrenaline and then superfused and stimulated by trains of 6 pulses, 100 Hz. 2. The ionotropic glutamate receptor agonists alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AM-PA; 10-100 microM), kainate (10-100 microM) and N-methyl-D-aspartate (NMDA; 30-300 microM) but not the metabotropic glutamate receptor agonist, 1-amino-1,3-cyclopentanedicarboxylate (ACPD; 10-100 microM) reduced the electrically evoked overflow of tritium. 3. The effects of AMPA, kainate and NMDA were attenuated or abolished by the adenosine A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) as well as by adenosine A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) as well as by adenosine deaminase but not by the alpha 2-adrenoceptor antagonist yohimbine, the gamma-aminobutyric acid (GABA) receptor antagonists, bicuculline and 2-hydroxysaclofen and the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). 4. The NMDA receptor antagonist, 2-amino-5-phosphonopentanoate (AP5) blocked the inhibitory effect of NMDA but not that of AMPA and kainate. The non-NMDA-receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked the effect of AMPA but not of kainate and NMDA. 5. In addition to decreasing the electrically evoked overflow of tritium, AMPA, kainate and NMDA but not ACPD caused a steep but transient rise of basal tritium efflux. This immediate releasing effect was not significantly changed by DPCPX, adenosine deaminase, yohimbine, bicuculline, 2-hydroxysaclofen and L-NAME (except that L-NAME enhanced the effect of kainate). AP5 and CNQX antagonized the immediate releasing effects in the same way that they antagonized the inhibition by AMPA, kainate and NMDA of the electrically evoked overflow of tritium.6. It is concluded that AMPA, kainate and NMDA, like glutamate, reduce the electrically evoked release of noradrenaline by releasing adenosine or an adenine nucleotide which is then degraded to adenosine. Activation of each of the three ionotropic glutamate receptors, AMPA, kainate and NMDA receptors, but not activation of metabotropic glutamate receptors can initiate this indirect inhibitory effect on the release of noradrenaline (as well as the known noradrenaline releasing effect).

Prejunctional modulation of noradrenaline release in mouse and rat vas deferens: contribution of P1- and P2-purinoceptors

1. Prejunctional purinoceptors modulating the release of noradrenaline were compared in mouse and rat vas deferens. Tissue slices were preincubated with [3H]-noradrenaline and then superfused and stimulated electrically, in most experiments by trains of 60 pulses, 1 Hz. 2. In mouse vas deferens, 2-chloroadenosine (IC50 0.24 microM), beta,gamma-methylene-ATP (IC50 3.8 microM), alpha,beta-methylene-ATP (IC50 2.9 microM) and 2-methylthio-ATP (only 30 microM tested) reduced the evoked overflow of tritium. 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX), 10 nM, antagonized the effect of 2-chloro-adenosine (apparent pKB 10.2) as well as of beta,gamma-methylene-ATP (apparent pKB 9.6) and alpha,beta-methylene-ATP. Suramin, 300 microM, attenuated the effect of 2-chloroadenosine at best very slightly, antagonized the effect of beta,gamma-methylene-ATP (apparent pKB 4.5) and, when combined with DPCPX 10 nM, caused a further marked shift to the right of the concentration-response curve of beta,gamma-methylene-ATP beyond the shift produced by DPCPX alone. 3. In rat vas deferens, 2-chloroadenosine (IC50 0.20 microM), beta,gamma-methylene-ATP (IC50 4.8 microM), alpha,beta-methylene-ATP (IC50 3.0 microM) and 2-methylthio-ATP (only 30 microM tested) also reduced the evoked overflow of tritium. DPCPX, 10 nM, antagonized the effect of 2-chloroadenosine (apparent pKB 9.7) as well as of beta,gamma-methylene-ATP (apparent pKB 9.6) and alpha,beta-methylene-ATP. Suramin, 300 microM, did not change the effect of 2-chloroadenosine, attenuated the effect of beta,gamma-methylene-ATP at best very slightly and, when combined with DPCPX, caused at best a very small shift to the right of the concentration-response curve of beta,gamma-methylene-ATP beyond the shift produced by DPCPX alone.4. It is concluded that prejunctional purinoceptor mechanisms in mouse and rat vas deferens are similar. In either species, both nucleosides such as adenosine and nucleotides such as beta,gamma-methylene-ATP activate a common release-inhibiting receptor which is a Pl- or, more specifically, A1-purinoceptor.There seems to be no need to postulate the existence of a novel prejunctional P3-purinoceptor.Moreover, the sympathetic terminal axons possess an additional P2-purinoceptor in both species which is activated by some nucleotides such as beta,gamma-methylene-ATP and 2-methylthio-ATP, although the activation of the P2-purinoceptor by beta,gamma-methylene-ATP is difficult to demonstrate in the rat.

Methoxamine inhibits noradrenaline release through activation of alpha 1- and alpha 2-adrenoceptors in rat isolated kidney: involvement of purines and prostaglandins

The effects of the alpha 1-adrenoceptor agonist methoxamine and the alpha 2-adrenoceptor agonist bromoxidine (UK 14034) on the stimulation induced (S-I) outflow of radioactivity at 100 Hz/6 pulses from rat isolated kidney preincubated with 3H-noradrenaline were investigated. Methoxamine (0.3-30 mumol/l) inhibited S-I outflow of radioactivity to a maximum of 83% with a pEC50 of 5.85 (5.71-5.94). UK 14304 (0.0003-0.3 mumol/l) inhibited S-I outflow of radioactivity to a maximum of 99% with a pEC50 of 8.35 (8.26-8.47). alpha-Adrenoceptor antagonist affinities (pKD) against methoxamine and UK 14304 at prejunctional alpha-adrenoceptors were determined. The concentration response curve of methoxamine was shifted to the right by the alpha 1/alpha 2B-adrenoceptor antagonist prazosin (0.1 mumol/l) with a pKD of 7.41 and that of UK 14304 by prazosin (0.3 mumol/l) with a pKD of 6.24. The alpha 2-adrenoceptor antagonist rauwolscine (0.1 mumol/l) shifted the concentration response curve of UK 14304 potently to the right with a pKD of 8.34. The concentration response curve of methoxamine was shifted also to the right by rauwolscine (0.1 mumol/l) and the alpha 2-adrenoceptor antagonist idazoxan (0.1 mumol/l), however, both antagonists suppressed the maximum response of methoxamine to 46% and 56%, respectively. A ten times lower concentration of rauwolscine (0.01 mumol/l) did not shift the concentration response curve of methoxamine but the inhibitory effect of methoxamine still reached only a maximum of 59%.(ABSTRACT TRUNCATED AT 250 WORDS)