Interaction of Guanine Nucleotides with [³H]Kainate and 6‐[³H]Cyano‐7‐Nitroquinoxaline‐2,3‐dione Binding in Goldfish Brain

Abstract

Recent reports have suggested that a major proportion of [3H]kainate binding in goldfish brain is to a novel form of G-protein-linked glutamate receptor. Here we confirm that guanine nucleotides decrease [3H]kainate binding in goldfish brain membranes, but that binding is also reduced to a similar extent under conditions where G-protein modulation should be minimised. Inclusion of GTP gamma S resulted in an approximately twofold decrease in the affinity of [3H]kainate binding and a 50% reduction in the apparent Bmax values in both Mg2+/Na+ and Mg2+/Na(+)-free buffer when assayed at 0 degrees C. The pharmacology of [3H]kainate binding is similar to that of well-characterised ionotropic kainate receptors but unlike that of known metabotropic glutamate receptors, with neither 1S,3R-amino-1,3-cyclopentanedicarboxylic acid (1S,3R-ACPD) nor ibotenic acid being effective competitors. The molecular mass of the [3H]kainate binding protein, as determined by radiation inactivation, was 40 kDa, similar to the subunit sizes of other lower vertebrate kainate binding proteins that are believed to comprise ligand-gated ion channels. Furthermore, GTP gamma S also inhibited the binding of the non-NMDA receptor-selective antagonist 6-[3H]cyano-7-nitroquinoxaline-2,3-dione. These data strongly suggest that the regulatory interaction between guanine nucleotides and [3H]kainate and 6-[3H]cyano-7-nitroquinoxaline-2,3-dione binding is complex and involves competition at the agonist/antagonist binding site in addition to any G-protein-mediated modulation.

Hyperglycemia alters E-NTPDases, ecto-5′-nucleotidase, and ectosolic and cytosolic adenosine deaminase activities and expression from encephala of adult zebrafish (Danio rerio)

“…For ecto-ADA experiments, encephalon was homogenized in 20 vol (v/w) of chilled phosphate-buffered saline (PBS), with 2 mM EDTA, 2 mM EGTA, and pH 7.4. The encephalic membranes were obtained as previously described [31]. The homogenates were centrifuged at 800×g for 10 min, and the supernatant fraction was subsequently centrifuged for 25 min at 40.000×g.…”

Differential effects of guanine nucleotides on kainic acid binding and on adenylate cyclase activity in chick optic tectum

“…However, in these cases, GMP, cGMP and adenine derivatives had no inhibitory effects, nor did guanine nucleotides modify the binding of the respective antagonists. In contrast, evidence has accumulated that suggests that the inhibitory effects of guanine nucleotides on the binding of glutamate and analogs, including antagonists, and on the the responses of intact cells to glutamate analogs, have unusual properties [5][6][7][8][9][10][11][12]. Studies on the interactions between glutamatergic systems and guanine nucleotides have shown that GMP, cGMP and guanosine may also inhibit the binding of glutamate or related agonists to membrane preparations [5,7,10]; furthermore, guanine nucleotides inhibit the binding of kainate by acting on the external surface in closed vesicle preparations [10].…”

“…This G protein-mediated inhibitory effect of GTP (or GDP) on agonist binding has been well demonstrated in many neurotransmitter systems [1,2]. In contrast, there are results indicating that guanine nucleotides may inhibit the binding of glutamate analogs [5][6][7][8][9][10][11][12] by mechanisms not involving G proteins.…”

Glyphosate-based herbicide affects biochemical parameters in Rhamdia quelen (Quoy & Gaimard, 1824 and) Leporinus obtusidens (Valenciennes, 1837)

“…The reaction was initiated by the addition of ATP or ADP, as the substrate, to obtain a final concentration of 10 mM. The activity of 5'-nucleotidase was determined, as described by Barnes et al (1993). The reaction was initiated by the addition of AMP, as the substrate, to a final concentration of 10 mM.…”