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At least 73 records · Page 4Linked to original sources
PubMed1980

Interaction of SQ 20009 and GABA-like drugs as modulators of benzodiazepine receptor binding.

SQ 20009, a new anxiolytic drug structurally unrelated to GABA or benzodiazepines, has two modulatory effects on the binding of 3H-flunitrazepam to membranes from rat cerebellum. Thus, SQ 20009 has a direct and chloride ion dependent stimulatory effect on benzodiazepine receptor binding which in turn appears to be modulated by the associated GABA receptor. In addition SQ 20009 has indirect effects on benzodiazepine receptor binding since it enhances the potency of GABA and muscimol to stimulate 3H-flunitrazepam binding.

Animals↗
PubMed1984

In vitro characterization of agonist, antagonist, inverse agonist and agonist/antagonist benzodiazepines.

The efficacy of coupling between the benzodiazepine receptor and chloride channel as well as the coupling to the GABA receptor is differentially affected by different benzodiazepine ligands. In general, the order of efficacy with regard to allosteric effects of benzodiazepine ligands on the chloride channel ([35S]TBPS) and GABA receptor ([3H]muscimol), is: agonist greater than agonist/antagonist greater than partial agonist greater than antagonist; with inverse agonists acting in a manner opposite to the classical benzodiazepine agonists. The chloride ionophore is allosterically modulated both by benzodiazepine and GABA receptors.

Animals↗
PubMed1977

Inhibitory effects of cyclic AMP on vasopressin release from the rat neural lobe in vitro.

The basal release of vasopressin from the isolated neural lobe of the rat decreased in the presence of exogenous cAMP, 8Br-cAMP, diB-cAMP, theophylline, SQ 20,009 and RO20-1724. The concentration-related decrease in vasopressin release, in the presence of phosphodiesterase inhibitors, was accompanied by a progressive increase in cAMP concentration in the neural lobe. The findings suggest a local modulation of vasopressin release from the neural lobes.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed1979

Cyclic 3',5'AMP phosphodiesterase in Physarum polycephalum. II. Kinetic properties.

Some kinetic characteristics of soluble and particulate cyclic 3',5'-AMP phosphodiesterases from Physarum polycephalum are presented. The nature of enzyme inhibition by various agents is reported. The relationship between various enzyme inhibitors and their reported chemotactic properties in Physarum is examined. The results suggest that the chemoattractant effect of several inhibitors may be related to their ability to inhibit the particulate and extracellular phosphodiesterases, but is unrelated to inhibition of the intracellular enzyme.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1993

Isobutylmethylxanthine and other classical cyclic nucleotide phosphodiesterase inhibitors affect cAMP-dependent protein kinase activity.

The effect of 17 inhibitors of cyclic nucleotide phosphodiesterases (PDEs) was assayed on cAMP binding activity of Mucor rouxii protein kinase A (PKA), on PKA activity in the absence of cAMP and on free catalytic subunit (C) activity. Isobutylmethylxanthine (IBMX), SQ 20,009 and cilostamide, at 0.2 mM, behaved as partial agonists of cAMP since they inhibited binding of 0.15 microM [3H]cAMP to the regulatory subunit (R), stimulated slightly PKA activity in the absence of cAMP and did not modify C activity. Amrinone at 0.2 mM inhibited C activity competitively towards ATP. These four compounds displayed the same effects when assayed on eukaryotic protein kinase A types I (PKI) and II (PKII). The combined effect of IBMX and cAMP was analysed on Mucor PKA. Under dissociating conditions (+ 0.5 M NaCl) IBMX antagonized activation by low concentrations of cAMP, while in the absence of NaCl, IBMX potentiated the stimulating activity of cAMP.

1-Methyl-3-isobutylxanthine↗
PubMed2006

Hydrolysis products of cAMP analogs cause transformation of Trypanosoma brucei from slender to stumpy-like forms.

African sleeping sickness is a disease caused by Trypanosoma brucei. T. brucei proliferate rapidly in the mammalian bloodstream as long, slender forms, but at higher population densities they transform into nondividing, short, stumpy forms. This is thought to be a mechanism adopted by T. brucei to establish a stable host-parasite relationship and to allow a transition into the insect stage of its life cycle. Earlier studies have suggested a role for cAMP in mediating this transformation. In this study, using membrane-permeable nucleotide analogs, we show that it is not the cAMP analogs themselves but rather the hydrolyzed products of membrane-permeable cAMP analogs that prevent proliferation of T. brucei. The metabolic products are more potent than the cAMP analogs, and hydrolysis-resistant cAMP analogs are not antiproliferative. We further show that the antiproliferative effect of these membrane-permeable adenosine analogs is caused by transformation into forms resembling short, stumpy bloodstream forms. These data suggest that the slender-to-stumpy transformation of T. brucei may not be mediated directly by cAMP and also raise the possibility of using such adenosine analogs as antitrypanosomal drugs.

Animals↗
PubMed1984

Hamster sperm Na+, K+-adenosine triphosphatase: increased activity during capacitation in vitro and its relationship to cyclic nucleotides.

These in vitro studies of golden hamster sperm were undertaken to determine whether: Na+, K+-adenosine triphosphatase (ATPase) activity is required for capacitation; Na+, K+-ATPase activity is altered during capacitation; and cyclic nucleotides can control this enzyme activity. Hamster sperm were incubated in a medium in which capacitation occurred in an asynchronous manner and in which acrosome reactions began to occur after approximately 3.5 h of incubation. Inhibition of the hamster sperm acrosome reaction by the Na+, K+-ATPase inhibitor ouabain (1 microM) added at Time (T) = 2 or T = 3 h could be fully reversed by the addition of the ionophore nigericin (0.1 microM) at T = 3.5 h. However, when ouabain was added at T = 0 or T = 1 h, similar nigericin addition could not completely reverse the inhibition. Na+, K+-ATPase activity of hamster sperm increased by 2 h of incubation (compared to that measured initially after 15 min) and this activity remained elevated at 3.5 h. Addition of either monobutyryl cyclic adenosine 3':5'-monophosphate ( BtcAMP ) (12.9 microM) or monobutyryl cyclic guanosine monophosphate ( BtcGMP ) (10.5 microM), or the phosphodiesterase inhibitor SQ20009 (10 microM) at 2 h produced a stimulation of acrosome reactions at 4 and 5 h. However, while BtcGMP and SQ 20009 also induced a further increase in Na+, K+-ATPase activity measured at 3.5 h, BtcAMP had no effect. Intracellular cAMP and cGMP levels measured showed cAMP increased by 2 h and remained elevated when measured at 3.5 h, while cGMP could not be consistently detected at 15 min, 2 h or 3.5 h. However, assays of high numbers of uncapacitated sperm did detect a low level of cGMP. These results suggest that Na+, K+-ATPase activity increases in and is essential for early capacitation [and thereby eventually for the acrosome reaction (AR)] of hamster sperm and that the increase in Na+, K+-ATPase activity occurring during capacitation is probably mediated by intracellular cGMP but not cAMP, although both cyclic nucleotides stimulate the hamster sperm AR.

Acrosome↗
PubMed1976

Cyclic AMP-phosphodiesterase and epidermal mitosis.

The relationship between cyclic AMP-phosphodiesterase (cAMP-PDE) inhibition and inhibition of epidermal mitosis was examined for several compounds using a soluble, low Km PDE activity from hairless mouse skin and the G2 mouse ear mitosis assay. Orders of potency determined at IC50 levels (concentrations required for 50% inhibition) were SQ 20009 greater than RO 20-1724 greater than papaverine greater than bufexamac greater than indomethacin greater than theophylline greater than p-biphenylylacetic acid greater than or less than glycyrrhetinic acid for inhibition of both PDE and mitosis. The disproportionately high antimitotic potency of puromycin relative to PDE inhibition was believed to reflect effects on protein biosynthesis. Activity of the three nonsteroidal anti-inflammatory agents (bufexamac, indomethacin, and p-biphenylylacetic acid) was unrelated to their effect on prostaglandin synthesis in homogenates of hairless mouse skin. The results suggest that the epidermal antimitotic activity of the compounds tested is related to their inhibition of cAMP-PDE and provide additional support for cAMP as a regulator of the G2 stage of the epidermal cell cycle.

3',5'-Cyclic-AMP Phosphodiesterases↗