Frank Watjen

A novel non-NMDA receptor antagonist shows selective displacement of low-affinity [3H]kainate binding

5-Nitro-6,7,8,9-tetrahydrobenzo[G]indole-2,3-dione-3-oxime (NS-102), a new competitive glutamate receptor antagonist displaced binding to non-N-methyl-D-aspartate (non-NMDA) binding sites with no activity at the NMDA and strychnine-insensitive glycine binding sites. Under experimental conditions in which both high- and low-affinity sites were labelled, NS-102 only partially inhibited the binding of [3H]kainate. Studies of NS-102 displacement of high-affinity versus low-affinity [3H]kainate binding showed a high selectivity of NS-102 for the low-affinity [3H]kainate binding site (Ki = 0.6 microM) compared to the high-affinity [3H]kainate binding site (Ki > 10 microM). NS-102 was a relatively weak inhibitor of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) binding (IC50 = 7.2 microM). NS-102 and related compounds with similar pharmacological profiles may become valuable tools in the characterization of the functional importance of the low-affinity [3H]kainate binding site.

NS 004 : an activator of Ca2+-dependent K+ channels in cerebellar granule cells

The large-conductance Ca(2+)-dependent K+ channels or BK channels in cerebellar granule cells were studied by patch-clamp technique, and the effects on channel activity of the molecule NS 004 (1-(2-hydroxy-5-chlorophenyl)-5-trifluoromethyl-2- benzimidazolone) were investigated. The channels had a unit conductance of 187 pS, were blocked by charybdotoxin and activated by internal Ca2+. NS 004 (10-30 microM) significantly increased the single channel opening frequency as well as the mean open time. In whole-cell recordings the compound shifted the BK current-voltage relationship by up to 40 mV towards negative membrane potentials. NS 004 is an efficient BK channel opener, which may represent a novel approach to relaxation of neuronal cells expressing this type of K+ channel.

Isatin oximes - A novel series of bioavailable non-NMDA antagonists

Abstract New isatin oximes are shown to be highly selective AMPA/kainate antagonists showing no antogonism of NMDA responses. In an AMPA seizure model in mice of the disclosed compounds has anticonvulsant effects both after i.v. and p.o. dosing.

Characterization of the binding of [3H]NS 257, a novel competitive AMPA receptor antagonist, to rat brain membranes and brain sections.

Abstract: The binding of [3H]NS 257 {1,2,3,6,7,8‐hexahydro‐3‐(hydroxyimino)‐N,N‐[3H]dimethyl‐7‐methyl‐2‐oxobenzo[2,1‐b:3,4‐c′] dipyrrole‐5‐sulfonamide} to rat cortical membranes was characterized in the absence and presence of thiocyanate. Specific [3H]NS 257 binding was saturable and reversible, and the stimulating effect of thiocyanate on binding was optimal at 100 mM. In the presence of thiocyanate [3H]NS 257 bound to a single population of binding sites with an affinity of 225 ± 8 nM and a binding site density of 0.61 ± 0.04 pmol/mg of original tissue. Thiocyanate increased the affinity of the binding site labeled by [3H]NS 257 for both α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) and l‐glutamate by a factor of 20 and 5, respectively. However, the affinity of the agonist domoate and the antagonists 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and 2,3‐dihydroxy‐6‐nitro‐7‐sulfamoylbenzo(f)‐quinoxaline (NBQX) was decreased in the presence of thiocyanate. Apparently, the affinities of antagonists as well as agonists for the AMPA receptor can be either increased or decreased by thiocyanate. The rank order of potency of the putative agonists quisqualate > AMPA > l‐glutamate > domoate > kainate and of the antagonists NBQX > CNQX is consistent with the labeling of AMPA receptors. Autoradiographic studies showed that the distribution of [3H]NS 257 binding sites in rat brain was similar to that of [3H]AMPA binding sites. NS 257 is the first AMPA antagonist to be described showing an increased affinity for the AMPA receptor in the presence of thiocyanate.