Differences in the adenosine receptors modulating inositol phosphates and cyclic AMP accumulation in mammalian cerebral cortex

Abstract

1 2-Chloroadenosine stimulated adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation and potentiated (guinea-pig) or inhibited (mouse) the histamine H1-receptor-stimulated hydrolysis of inositol phospholipids in slices of guinea-pig and mouse cerebral cortex. 2 Two xanthine-based adenosine receptor antagonists were identified which were one order of magnitude more potent at the adenosine receptor mediating augmentation of the histaminestimulated inositol phospholipid hydrolysis than at the receptor linked to cyclic AMP formation in guinea-pig cerebral cortical slices.3 These compounds, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and 7-benzyl-3-(2-methylpropyl)xanthine (BMPX) retained their selectivity under near-identical incubation conditions in both assays. 4 These compounds also showed similar affinities and selectivity for the adenosine receptor mediating inhibition of histamine-stimulated inositol phospholipid hydrolysis in mouse cerebral cortical slices.5 Inclusion of agents which give rise to, or mimic, high levels of cyclic AMP (forskolin (1 gM), 8-bromo-cyclic AMP (1 mM) and vasoactive intestinal polypeptide (1 pM)) in the incubation medium failed to mimic the action of 2-chloroadenosine on inositol phospholipid turnover in cerebral cortical slices from either species. 6 These data suggest that the adenosine receptor modulating the hydrolysis of inositol phospholipid in mouse and guinea-pig cerebral cortical slices is different from the adenosine receptor linked to cyclic AMP formation, and, furthermore, that the modulation of inositol phospholipid metabolism in either species is not mediated via alterations in cyclic AMP levels.

(−)‐Discretamine, a selective α1D‐adrenoceptor antagonist, isolated from Fissistigma glaucescens

“…Incubation was terminated by stop buffer and addition of 0.1 N HCl (1:1 v/v). Cells were left a minimum of 30 min at -20°C before isolation of total [3H]-inositol phosphates by anion exchange chromatography (Alexander et al, 1989).…”

A1 adenosine receptor inhibition of cyclic AMP formation and radioligand binding in the guinea‐pig cerebral cortex

“…Apparent inhibition constants were calculated from radioligand binding data using the ChengPrusoff transformation (Cheng & Prusoff, 1973). Functional affinity constants were calculated as previously described (Alexander et al, 1989 Figure 2). Thus, R-PIA, CCPA and CPA in the concentration range 1-1000 nm all inhibited the forskolin response to a maximal level of 82 ± 3, 92 ± 4, and 91 ± 2% inhibition, respectively ( [3H]-adenine-prelabelled slices were incubated with increasing concentrations of R-PIA (0), S-PIA (A), NECA (0) and higher concentrations of R-PIA, CCPA and CPA is presumably mediated through activation of A2b adenosine receptors (Jacobson et al, 1992;Alexander et al, 1994).…”

Natriuretic peptide‐induced cyclic GMP accumulation in adult guinea‐pig cerebellar slices

“…Slices were equilibrated with Krebs-bicarbonate buffer for 60min and distributed as 251il aliquots into flat-bottomed vials in the presence of [3H]-inositol (40kBqml-') and LiCl (5 mM) to a final volume of 300 gl, as previously described (Alexander et al, 1989 (n = 7, P<0.01) and 208 ± 10 (n = 3, P<0.01) % over the control levels, respectively. CNP significantly stimulated [3H]-cyclic GMP production only at concentrations greater than 10 lM in the presence of 0.5 mM IBMX (at 10 JAM, 80 ± 10% over control, n = 3, P < 0.05).…”