adenosine-5--(n-ethylcarboxamide) and alpha-beta-methyleneadenosine-5--triphosphate

Adenosine receptors involved in modulation of contractions were characterized in the bisected rat vas deferens by combining pharmacological and immunohistochemical approaches. In both portions, noradrenaline-elicited contractions were enhanced by the adenosine A(1) receptor agonist N(6)-cyclopentyladenosine (CPA), and inhibited by the non-selective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) in the presence of the adenosine A(1) receptor antagonist 1,3-dipropyl-8-cyclopentyl-l,3-dipropylxanthine (DPCPX). The adenosine A(2A) receptor agonist 2-p-(2-carboxyethyl)phenethyl-amino-5'-N-ethylcarboxamidoadenosine (CGS 21680) also inhibited noradrenaline-elicited contractions but only in the prostatic portion. Contractions elicited by the stable ATP analogue alpha,beta-methyleneATP (alpha,beta-MeATP) were inhibited only by NECA in the presence of DPCPX and only in the prostatic portion. This study provides functional evidence for the presence, in both portions of the rat vas deferens, of an adenosine A(1) receptor-mediated enhancement and of an adenosine A(2) receptor-mediated inhibition of contractions. The latter effect is mediated by both A(2A) and A(2B) subtypes in the prostatic portion but only by the A(2B) subtype in the epididymal portion. This regional variation is supported by the immunohistochemical results that revealed an adenosine A(2A) receptor immunoreactivity not co-localized with nerve fibres more abundant in the prostatic than in the epididymal portion.

Topics: Adenosine; Adenosine Triphosphate; Adenosine-5'-(N-ethylcarboxamide); Animals; Epididymis; Immunohistochemistry; In Vitro Techniques; Male; Muscle Contraction; Norepinephrine; Phenethylamines; Prostate; Rats; Rats, Wistar; Receptor, Adenosine A2A; Receptors, Purinergic P1; Theobromine; Triazines; Triazoles; Vas Deferens; Xanthines

The effects of extracellular ATP, ADP, AMP and adenosine on cAMP accumulation have been studied in freshly isolated B-lymphocytes from patients with chronic lymphocytic leukemia. Extracellular ATP and several nucleotide analogs stimulated cAMP accumulation with the following order of potency: ATP (EC(50)=120+/-20 microM)>ADP>>AMP. ADP was less effective than ATP and may be a partial agonist. AMP exhibited variable but generally weak activity. The stable analog of ATP, alpha,beta-methylene ATP (EC(50)=110+/-15 microM) also stimulated cAMP accumulation and exhibited similar efficacy to ATP. The P2Y(2) receptor agonist, UTP had no effect on intracellular cAMP levels. Adenosine and the A(2A)/A(2B) receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) also stimulated cAMP accumulation in CLL lymphocytes. Adenosine deaminase inhibited the cAMP response to adenosine but had no effect on the ATP-induced cAMP response. On the other hand, the AMP analog, adenosine 5'-thiomonophosphate, (AMPS; 1.0 mM) inhibited ATP-induced and alpha,beta-methylene ATP-induced cAMP production but had no effect on adenosine-induced cAMP production. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed the presence of P2Y(11) receptor as well as A(2A) and A(2B) receptor mRNA in chronic lymphocytic leukemia lymphocytes. However, A(2B) receptors would appear to be relatively ineffective because the A(2A) selective agonist, CGS-21680 exhibited comparable efficacy to NECA. Furthermore, the A(2A)-selective antagonist 8-(3-chlorostyryl)-caffeine (CSC) right-shifted the concentration-response curve for NECA. Taken together, the data indicate that ATP induces cAMP accumulation via the activation of P2Y(11) receptors whereas adenosine induces cAMP accumulation via the activation of A(2A) receptors. Coordinate activation of P2Y(11) and A(2A) receptors may influence the developmental fate of normal B-lymphocytes.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Adenosine; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Adenosine-5'-(N-ethylcarboxamide); Cyclic AMP; Dose-Response Relationship, Drug; Gene Expression; Humans; Leukemia, Lymphocytic, Chronic, B-Cell; Lymphocytes; Purinergic P2 Receptor Antagonists; Receptors, Purinergic P2; Receptors, Purinergic P2X7; RNA, Messenger

The vasoactive properties of P1,P4-diadenosine tetraphosphate (Ap4A) were studied by measuring the effects of perfusion pressure of a rat isolated perfused kidney.. The vasoconstrictive response to Ap4A was mediated to a large extent to a P2X receptor which could be shown by inhibition with pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid tetrasodium. The remaining vasoconstriction of Ap4A could be blocked by a 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective A1 receptor antagonist In raised tone preparation Ap4A evoked vasodilation when P2 receptors were blocked by suramin. The dilation was not mediated by a P2Y receptor as the effect could not be blocked by suramin.. Ap4A induces vasoconstriction via A1 and P2X receptors and vasodilatation via an unidentified receptor which is not a P2Y receptor. Ap4A may play an important role in kidney perfusion and, thus, in blood-pressure control.

Topics: Adenosine Triphosphate; Adenosine-5'-(N-ethylcarboxamide); Animals; Dinucleoside Phosphates; In Vitro Techniques; Male; Perfusion; Pyridoxal Phosphate; Rats; Rats, Inbred WKY; Receptors, Purinergic; Receptors, Purinergic P1; Receptors, Purinergic P2; Renal Artery; Thionucleotides; Vasoconstrictor Agents; Vasodilator Agents; Xanthines

A high-affinity binding site for 5'-N-ethylcarboxamido[3H]adenosine ([3H]NECA) from bovine cerebral cortex has been characterized in its membrane-bound and solubilized state after gel filtration on Sepharose CL-6B. For detection of this site in membranes, it was necessary to remove metabolites with high affinities for this site enzymatically, e.g., adenosine by addition of adenosine deaminase and inosine by addition of nucleoside phosphorylase. The pore-forming peptide antibiotic alamethicin further enhanced binding of [3H]NECA to this site in membranes. In contrast to adenosine receptors and the adenotin-like low-affinity binding protein, this novel site was extremely sensitive against treatment with the sulfhydryl alkylating agent N-ethylmaleimide. In competition experiments, this site could be differentiated from adenosine receptors by its high affinity for adenine nucleotides and its lack of affinity for adenosine receptor antagonists. Inosine and its derivative S-(4-nitrobenzyl)-6-thioinosine were relatively potent ligands with Ki values in the high nano- and low micromolar range, respectively. We conclude that the high-affinity NECA binding site described previously in bovine striatum is not exclusively located in the striatum, but can also be detected in membrane preparations and soluble extracts of bovine brain cortex.

Topics: Adenosine; Adenosine Triphosphate; Adenosine-5'-(N-ethylcarboxamide); Animals; Binding Sites; Cattle; Cell Membrane; Cerebral Cortex; Cytosol; Ethylmaleimide; Guanine Nucleotides; Kinetics; Radioligand Assay; Tritium