1,3,8‐ and 1,3,7‐substituted xanthines: relative potency as adenosine receptor antagonists at the frog neuromuscular junction

Sebastião, Ana M.; Ribeiro, J.A.

doi:10.1111/j.1476-5381.1989.tb11802.x

Cited by 37 publications

(16 citation statements)

References 26 publications

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“…This agrees with the idea that the adenosine receptor mediating inhibition of neurotransmitter release is not coupled to adenylate cyclase (see e.g. Ribeiro & Sebastiao, 1989).…”

Section: Discussionsupporting

confidence: 92%

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Interactions between adenosine and phorbol esters or lithium at the frog neuromuscular junction

Sebastião¹,

Ribeiro²

1990

British J Pharmacology

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1 Interactions between the effects of adenosine or 2-chloro-adenosine (CADO) and the effects of substances that interfere with the phosphoinositides/protein kinase C transducing system or with the adenylate cyclase transducing system, on endplate potentials (e.p.ps), were investigated. The preparation used was the innervated sartorius muscle of the frog in which twitches had been prevented with high magnesium concentrations.2 The activator of protein kinase C, 4f,-phorbol-12,13-diacetate (PDAc) 7 The results suggest that the phosphoinositides/protein kinase C transducing system, but not the adenylate cyclase transducing system, might be involved in the inhibitory effect of adenosine on neuromuscular transmission.

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“…This agrees with the idea that the adenosine receptor mediating inhibition of neurotransmitter release is not coupled to adenylate cyclase (see e.g. Ribeiro & Sebastiao, 1989).…”

Section: Discussionsupporting

confidence: 92%

“…amplitude caused by 0.5 pg ml 1, lugml-' and 2.5pgml-1 of polymyxin B were 8 + 1.0% (n = 2), 19 + 1.4% (n = 6) and 31 + 2.0% (n = 2) respectively. The quantal content (determined by the variance method) of Ribeiro, 1989). Ki values were taken as the negative antilog of the pA2 value.…”

Section: H-7 and Polymyxin Bmentioning

confidence: 99%

Interactions between adenosine and phorbol esters or lithium at the frog neuromuscular junction

Sebastião¹,

Ribeiro²

1990

British J Pharmacology

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“…The rank order of potency of antagonists found was: 8-phenyltheophylline>xanthine amino congener (XAC)= DPCPX = CGS15943>isobutyl methylxanthine (IBMX) > > theophylline. The similar potency of XAC and DPCPX can be compared to that corresponding to A3 receptors, although the Ki values obtained with BBM in our displacement experiments are higher than those reported from functional studies for the A3 receptor (Sebastiao & Ribeiro, 1989). What is still evident is that the order for antagonists does not coincide with those which are well established for Al (DPCPX> xanthine amino congener> theophylline) and A2 (CGS15943>xanthine amino con-gener> DPCPX> theophylline) receptors.…”

Section: Discussioncontrasting

confidence: 48%

“…Metabolism was monitored at the end of incubation period (see Figure 1); at this time more than 18% of added AP4A and more than 55% of added AP5A was not metabolized. As shown in Table 3 Pertussis toxin (pg ml1) (Sebastiao & Ribeiro, 1989). What is still evident is that the order for antagonists does not coincide with those which are well established for Al (DPCPX> xanthine amino congener> theophylline) and A2 (CGS15943>xanthine amino congener> DPCPX> theophylline) receptors.…”

Section: Discussionmentioning

confidence: 90%

Characterization of adenosine receptors in brush‐border membranes from pig kidney

Blanco

Canela

Mallol

et al. 1992

British J Pharmacology

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“… a Bruns et al, 1987; b Haleen et al, 1987; c Lee and Reddington, 1986; d Jacobson et al, 1993 a ; e Bruns et al, 1986; f Ukena et al, 1986; g Choi et al, 1988; h Seale et al, 1988; i Sebastiao and Ribeiro, 1989; j Jacobson et al, 1993 b . …”

Section: Effects Of Adenosine Antagonists On Neca‐induced Cis‐cos Myomentioning

confidence: 99%

Adenosine Stimulates Cone Photoreceptor Myoid Elongation via an Adenosine A2‐Like Receptor

Rey

Burnside

1999

Journal of Neurochemistry

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Abstract:In several parts of the nervous system, adenosine has been shown to function as an extracellular neuromodulator binding to surface receptors on target cells. This study examines the possible role of adenosine in mediating light and circadian regulation of retinomotor movements in teleost cone photoreceptors. Teleost cones elongate in the dark and contract in the light. In continuous darkness, the cones continue to elongate and contract at subjective dusk and dawn in response to circadian signals. We report here that exogenous adenosine triggers elongation (the dark/ night movement) in isolated cone inner segment-cone outer segment preparations (CIS-COS) in vitro. Agonist/ antagonist potency profiles indicate that adenosine's effect on cone movement is mediated by an A2-like adenosine receptor, which like other A2 receptors enhances adenylate cyclase activity. Although closest to that expected for A2 receptors, the antagonist potency profile for CIS-COS does not correspond exactly to any known A2 receptor subtype, suggesting that the cone receptor may be a novel A2 subtype. Our findings are consistent with previous reports that retinal adenosine levels are higher in the dark, and further suggest that adenosine could act as a neuromodulatory "dark signal" influencing photoreceptor metabolism and function in the fish retina. Key Words: Adenosine-A2 receptors-Cone-Photoreceptor-Motility-Circadian. J. Neurochem. 72, 2345Neurochem. 72, -2355Neurochem. 72, (1999.In the teleost retina, photoreceptors elongate and contract in response to changes in light condition. Cones elongate in the dark and contract in the light; rods elongate in the light and contract in the dark (see Ali, 1975;Burnside and Nagle, 1983;Burnside and Dearry, 1986). These "retinomotor movements" serve to position the photopigment-bearing outer segments of the appropriate photoreceptors first in line for light absorption in either bright light conditions (cones first) or dim light conditions (rods first). Elongation and contraction take place in the neck-like myoid region between the photoreceptor's nucleus and outer segment. Cone motility is regulated not only by light, but also by circadian signals. Even when fish are maintained in constant darkness, their cones continue to elongate at subjective dusk and contract at subjective dawn (see Ali, 1975;Burnside and Ackland, 1984;Douglas et al., 1992).Cyclic AMP (cAMP) appears to play a critical role in the regulation of cone motility. Experimental treatments that elevate cAMP induce cones to elongate (i.e., elevating cAMP mimics the effect of darkness or subjective night) (Burnside et al., 1982;Burnside and Ackland, 1984;Dearry and Burnside, 1984). Exposing retinas or isolated cones to dopamine induces cones to contract even in constant darkness (i.e., dopamine mimics the effect of light or subjective day) (Dearry and Burnside, 1985;Pierce and Besharse, 1985;Dearry and Burnside, 1986b). Pharmacological studies of myoid contraction in isolated cone inner segment-cone outer segment preparations ...

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1,3,8‐ and 1,3,7‐substituted xanthines: relative potency as adenosine receptor antagonists at the frog neuromuscular junction

Cited by 37 publications

References 26 publications

Interactions between adenosine and phorbol esters or lithium at the frog neuromuscular junction

Interactions between adenosine and phorbol esters or lithium at the frog neuromuscular junction

Characterization of adenosine receptors in brush‐border membranes from pig kidney

Adenosine Stimulates Cone Photoreceptor Myoid Elongation via an Adenosine A2‐Like Receptor

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