cyclic-gmp and 2-amino-4-phosphonobutyric-acid

Chromatic aspects of receptive field size in the H1 horizontal cell syncytium of the carp retina were investigated using spectral photostimuli (blue or red) presented in the form of either a pair of a small spot and annulus, or a narrow moving slit. In the light-adapted retina, the receptive field for the blue stimulus was found to be significantly smaller than that for the red, i.e. there was a chromatic difference in the receptive field size. During the course of dark adaptation, the overall receptive field size increased, but the chromatic difference decreased. Immediately after adaptation to bright light, the receptive field sizes were reduced significantly, but the chromatic difference increased, mainly due to a greater reduction in the receptive field for the blue stimulus. Application of dopamine (5 microM) to a dark-adapted retina gradually decreased the receptive field size for both colours, but the chromatic difference became larger, again due to a greater reduction in the receptive field size for the blue stimulus. 2-Amino-4-phosphonobutyrate (APB) applied to light-adapted retinae at a working concentration of 1 mM, greatly expanded the receptive field size and suppressed the chromatic difference due to the effect being greater for the receptive field for the blue stimulus. The effect of APB was slow and cumulative. On the other hand, intracellular injection of cGMP or dibutyryl-cGMP increased the chromatic difference in the receptive field size. It is suggested (i) that the chromatic difference in the receptive field size could be due to a cGMP-coupled, conductance-decreasing receptor mechanism activated by APB; and (ii) that the mechanism is associated with short-wavelength sensitive cone input to the H1 cells and operates in the light-adapted state of the retina.

Topics: Adaptation, Ocular; Aminobutyrates; Animals; Carps; Color Perception; Cyclic GMP; Darkness; Dibutyryl Cyclic GMP; Dopamine; Excitatory Amino Acid Agonists; In Vitro Techniques; Light; Neurons; Regression Analysis; Retina; Visual Fields

The effects of the group III mGluR agonist, L-2-amino-4-phosphonobutyrate (L-AP4), on depolarization-stimulated cGMP levels in adult rat cerebellar slices were determined. L-AP4 elicited a concentration-dependent, complete inhibition of cGMP formation stimulated by 4-aminopyridine (4-AP; 1 mM), yielding an IC50 value of 4.2 +/- 1.6 microM (n = 3). The 4-AP response was also reduced by the P-type Ca2+ channel toxins omega-conotoxin MVIIC (3 microM; 39 +/- 7% inhibition) and omega-Agatoxin IVA (30 nM; 53 +/- 4%), and was abolished in the absence of Ca2+ or in the presence of Co2+. The inhibitions of the 4-AP cGMP response by 10 microM L-AP4 and 30 nM omega-Agatoxin IVA were not additive, indicating that part of the actions of L-AP4 in the cerebellum involves the modulation of P-type Ca2+ channels.

Topics: 4-Aminopyridine; Aminobutyrates; Animals; Calcium Channel Blockers; Cerebellum; CHO Cells; Cricetinae; Cyclic GMP; Excitatory Amino Acid Antagonists; In Vitro Techniques; Male; Nitroprusside; omega-Agatoxin IVA; omega-Conotoxins; Peptides; Rats; Rats, Sprague-Dawley; Spider Venoms; Vasodilator Agents

Glutamate, the neurotransmitter released by photoreceptors, excites horizontal cells and OFF-type bipolar cells by activating ionotropic receptors. This study investigated an additional action of glutamate in which it modulates a voltage-gated ion channel in horizontal cells. We find that glutamate and APB (2-amino-4-phosphonobutyrate) produce a delayed and moderately prolonged suppression of an inward rectifier current (IRK+). This effect is proposed to occur via an APB-sensitive metabotropic glutamate receptor (mGluR) because common agonists for the ionotropic or APB-insensitive mGluRs are ineffective and the APB-insensitive receptor antagonist alpha-methyl-4-carboxyphenylglycine (MCPG) does not block the actions of glutamate or APB. 8-Br-cGMP, 1-methyl-3-isobutylxanthine (IBMX), and atrial natriuretic peptide (ANP) but not 8-Br-cAMP mimic the suppression of IRK+. The effects of glutamate and APB are blocked by protein kinase inhibitors including Rp-8-pCPT-cGMPS, H-8, and H-7 as well as by ATPgammaS. We hypothesize that the APB receptor suppresses IRK+ via upregulation of cGMP and subsequent activation of a cGMP-dependent protein kinase. This pathway is likely regulated by an ATP-dependent phosphorylation. This is a novel signaling pathway for mGluRs and indicates that at least two distinct APB-activated pathways exist in the retina. Functionally, this APB receptor-mediated action found in horizontal cells would provide a means by which spatially restricted changes of glutamate, produced by local illumination of photoreceptors, could regulate IRK+ and consequently the response properties of these neurons. This would serve to adapt selectively retinal regions stimulated by small regions of the visual world.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; 1-Methyl-3-isobutylxanthine; 8-Bromo Cyclic Adenosine Monophosphate; Adenosine Triphosphate; Aminobutyrates; Animals; Atrial Natriuretic Factor; Benzoates; Cyclic GMP; Enzyme Inhibitors; Glutamic Acid; Glycine; Ictaluridae; Ion Channel Gating; Isoquinolines; Models, Neurological; Patch-Clamp Techniques; Photoreceptor Cells; Potassium Channels; Receptors, Metabotropic Glutamate; Second Messenger Systems; Thionucleotides

1. Facilitation of the N-methyl-D-aspartate (NMDA) receptor-mediated depolarization of cortical neurones induced by metabotropic glutamate receptor (mGluR) agonists in the presence of tetrodotoxin has been examined by use of grease-gap recording. 2. Quisqualate (1-2 microM) and 10 to 100 microM 1S,3R-I-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) facilitated the NMDA-, but not the kainate-induced depolarization with an EC50 of 16 microM for 1S,3R-ACPD. The facilitation induced by quisqualate was reduced, but not blocked, by 4 microM 6-cyano-7-nitroquinoxaline-2,3-dione. 3. D,L-2-Amino-3-phosphonopropionic acid and D,L-2-amino-4-phosphonobutyric acid antagonized the 1S,3R-ACPD facilitation in a non-competitive manner with IC50 values of 0.24 microM and 4.4 microM respectively. 4. Homologous desensitization of the 1S,3R-ACPD induced facilitation was not observed. The facilitation was not altered by 10 nM staurosporine or 3 microM phorbol diacetate. 5. Substitution of 20 microM 8-bromo-cyclic adenosine monophosphate, 20 microM 8-bromo-cyclic guanosine monophosphate, or 10 microM arachidonic acid for 1S,3R-ACPD did not induce facilitation of the NMDA response. However, the 1S,3R-ACPD facilitation was potentiated by 10 mM myo-inositol and exhibited heterologous desensitization following exposure to 100 microM 5-hydroxytryptamine. 6. The 1S,3R-ACPD-induced facilitation persisted in both 10 microM nifedipine and nominally Ca(2+)-free medium and was only gradually eliminated following addition of 100 microM bis-(-o-aminophenoxy)-ethane-N,N,N,N-tetraacetic acid in Ca(2+)-free medium. Facilitation of the NMDA response induced by carbachol, but not phenylephrine, was also observed in nominally Ca(2+)-free medium. Perfusing 50 microM bis-(-aminophenoxy)-ethane-N,N,N,N-tetraacetic acid aminoethoxy eliminated the 1S,3R-ACPD facilitation. 7. These experiments have shown that mGluR agonists selectively facilitate the NMDA depolarization of cortical wedges, most likely by activating one or more mGluR subtypes that couple to phospholipase C. We conclude the facilitation results from a Ca(2+)-sensitive mechanism dependent on activation of phospholipase C and release of internal Ca2+. The facilitation is not contingent on activation of protein kinase C or entry of Ca2+ through nifedipine-sensitive Ca2+ channels.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Alanine; Alkaloids; Aminobutyrates; Animals; Cerebral Cortex; Cyclic GMP; Cycloleucine; Male; Neurons; Phorbol Esters; Quisqualic Acid; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Staurosporine

Whole-cell patch-clamp recordings were obtained from on-bipolar cells in, or isolated from, retinal slices prepared from dogfish retina. The properties of the cGMP-activated conductance of on-bipolar cells were compared with that of rod photoreceptors. The on-bipolar cell cGMP-activated channel was blocked by L-cis-diltiazem, a block which was strongly voltage dependent. However, this channel is not identical with that of photoreceptors. The location of the L-cis-diltiazem blocking site and its accessibility in the channel are not the same as in rods. The voltage dependence of block suggests that the blocking site, although near the intracellular side of the channel, is accessible to the positively charged form of L-cis-diltiazem only from the outward facing side of the channel. Furthermore, in contrast to rod channels, the conductance of the on-bipolar cell channels is unaltered by the removal of external divalent cations.

Topics: Aminobutyrates; Animals; Calcium; Cations, Divalent; Cesium; Chlorides; Cyclic GMP; Dendrites; Diltiazem; Dogfish; Egtazic Acid; In Vitro Techniques; Magnesium; Membrane Potentials; Photoreceptor Cells; Retina; Synapses

Transmitter release from photoreceptors is decreased by light, resulting in a conductance increase in depolarizing bipolar cells. Addition of exogenous cGMP through a patch pipette to depolarizing bipolar cells from slices of dark-adapted tiger salamander retina resulted in an enhancement of the light response. This enhancement was blocked by GTP-gamma-S and dipyridamole, an inhibitor of phosphodiesterase. GTP-gamma-S and dipyridamole also blocked responses to exogenously applied 2-amino-4-phosphonobutyrate (APB), the glutamate agonist selective for this receptor. These data support the hypothesis that the postsynaptic receptor is linked via a G protein to a phosphodiesterase. The binding of glutamate or APB to the receptor suppresses a cGMP-activated current by increasing the rate of cyclic nucleotide hydrolysis.

Topics: Alkaloids; Aminobutyrates; Animals; Cyclic GMP; Dark Adaptation; Dipyridamole; Electric Conductivity; Electrophysiology; Guanosine 5'-O-(3-Thiotriphosphate); Light; Neurotransmitter Agents; Phorbol Esters; Photoreceptor Cells; Retina; Staurosporine

Depolarizing bipolar cells (DBCs) of the retina are the only neurons in the vertebrate central nervous system known to be hyperpolarized by the neurotransmitter glutamate. Both glutamate and its analogue L-2-amino-4-phosphonobutyrate (APB) hyperpolarize DBCs by decreasing membrane conductance. Furthermore, glutamate responses in DBCs slowly decrease during whole-cell recording, suggesting that the response involves a second messenger system. Here we report that intracellular cyclic GMP or GTP activates a membrane conductance that is suppressed by APB, resulting in an enhanced APB response. In the presence of GTP-gamma-S, APB causes an irreversible suppression of the conductance. Inhibitors of G-protein activation or phosphodiesterase activity decrease the APB response. Thus, the DBC glutamate receptor seems to close ion channels by increasing the rate of cGMP hydrolysis by a G protein-mediated process that is strikingly similar to light transduction in photoreceptors.

Topics: 1-Methyl-3-isobutylxanthine; Aminobutyrates; Animals; Cell Membrane; Cyclic GMP; Electric Conductivity; Glutamates; Glutamic Acid; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Photoreceptor Cells; Receptors, Glutamate; Receptors, Neurotransmitter; Retina; Second Messenger Systems; Thionucleotides; Urodela

The effects of purine nucleotides on the binding of DL-[3H] 2-amino-4-phosphonobutyrate (DL-[3H] APB) to rat brain membranes were investigated. Certain guanine nucleotides, especially cyclic GMP and GTP, were found to be potent inhibitors of binding. Kinetic studies revealed that both cyclic GMP and GTP acted to decrease receptor affinity without affecting significantly binding site density. These endogenous substances may therefore play an important role in the regulation of excitatory amino acid receptor function.

Topics: Aminobutyrates; Animals; Brain; Cyclic GMP; Female; Guanosine Triphosphate; In Vitro Techniques; Kinetics; Male; Purine Nucleotides; Rats; Rats, Inbred Strains; Receptors, Glutamate; Receptors, Neurotransmitter; Synaptic Membranes; Tritium

An examination was made of the ability of phosphonate analogues of acidic amino acids to interact with excitatory amino acid receptors, employing binding assays for [3H]glutamate and [3H]aspartate and by investigating the inhibitory effects of these compounds on the stimulation of cerebellar cyclic GMP levels. In both systems the phosphonates exhibited inhibitory activity, although the cGMP system corresponded better with electrophysiological data. The higher homologues (e.g. 2-amino-5-phosphonovalerate) showed high selectivity for NMDA-type receptors and this effect was stereospecific, with the (-)-isomers being at least 4-7 times more active than the (+)-forms.

Topics: 2-Amino-5-phosphonovalerate; Alanine; Amino Acids; Aminobutyrates; Animals; Cerebellum; Cyclic GMP; Rats; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, Neurotransmitter; Stereoisomerism; Valine