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M Sokolovsky

Publications and source records attributed to M Sokolovsky.

At least 73 records · Page 4Linked to original sources
PubMed1989

Sarafotoxin receptors mediate phosphoinositide hydrolysis in various rat brain regions.

Sarafotoxin-b, a potent snake vasoconstrictor peptide homologous to the mammalian endothelial vasoconstrictor endothelin, induces phosphoinositide (PI) hydrolysis in various brain regions of the rat. Sarafotoxin-b induced PI hydrolysis is largely independent of extracellular Ca2+ and is detected in all brain regions where toxin-binding sites are found. These results point to the existence of a hitherto undetected neuroreceptor associated with the PI cycle.

Animals↗
PubMed1989

Nonpsychotropic cannabinoid acts as a functional N-methyl-D-aspartate receptor blocker.

Binding studies using the enantiomers of the synthetic cannabinoid 7-hydroxy-delta 6-tetrahydrocannabinol 1,1-dimethylheptyl homolog in preparations of rat brain cortical membranes reveal that the (+)-(3S,4S) enantiomer HU-211 blocks N-methyl-D-aspartate (NMDA) receptors in a stereospecific manner and that the interaction occurs at binding sites distinct from those of other noncompetitive NMDA antagonists or of glutamate and glycine. Moreover, HU-211 induces stereotype and locomotor hyperactivity in mice and tachycardia in rat, effects typically caused by NMDA receptor antagonists. HU-211 is also a potent blocker of NMDA-induced tremor, seizures, and lethality in mice. This compound may therefore prove useful as a nonpsychoactive drug that protects against NMDA-receptor-mediated neurotoxicity.

Animals↗
PubMed1989

Vascular cholinesterases and choline uptake in isolated rat forebrain microvessels: a possible link.

The two parameters of the active [methyl-3H]choline uptake into isolated rat forebrain microvessels, Km and Vmax, were determined for 1-, 3-, 10-, and 24-month-old Charles River male rats and compared with the activities of the enzymes choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) in these microvessels over the same time course. The value of Km remained constant over the entire period, but that of Vmax increased from 8.5 +/- 1.0 to 80.6 +/- 16.4 nmol g-1 (mean +/- SEM) over the first 3 months of life. Over the same period, the increase in ChAT activity, from an initial value of 7.1 +/- 1.6 to 10.2 +/- 0.3 nmol g-1 min-1, was not proportional to that of choline uptake. Levels of BuChE activity (0.9-1.3 mumol g-1 min-1) were almost unchanged throughout the entire 24-month period, but those of AChE showed a steady and significant increase from 1 to 24 months, remaining relatively high at senescence (4.7 mumol g-1 min-1), when choline uptake had decreased to one-third of its optimal value. Selective inhibition of AChE with 1,5-bis(4-allyldimethylammonium-phenyl)pentan-3-one dibromide (0.5 microM) in unruptured capillaries from 3-month-old rats resulted in a decrease in Vmax of choline uptake from approximately 81 to 59 nmol g-1 min-1 or with 9-amino-1,2,3,4-tetrahydroacridine (10 microM) in capillaries from 2-month-old rats from approximately 30 to 15 nmol g-1 min-1. Selective inhibition of BuChE with tetraisopropyl pyrophosphoramide (100 microM) resulted in an increase in Vmax from approximately 81 to 96 nmol g-1 min-1. It is possible that the two vascular enzyme systems are coupled to a hypothetical endothelial choline transporter, but with an action opposite to each other.

Aging↗
PubMed1989

Postnatal changes in muscarinic receptor subtype mRNAs in rat brain and heart.

Expression of mRNAs for the muscarinic acetylcholine receptor subtypes in various brain regions and in the heart of male rats was examined during postnatal development. The mRNAs for the four subtypes displayed different developmental patterns in the different regions, depending both on the cell type composition and on the age of the brain region examined.

Aging↗
PubMed1988

Characterization and localization of a novel neuroreceptor for the peptide sarafotoxin.

We have recently shown that the rat atrium and brain contain specific high affinity receptors for the novel snake vasoconstrictor peptide sarafotoxin-b (SRTXb), and demonstrated toxin-induced phosphoinositide hydrolysis. Here we report on the characteristics of 125I-SRTXb receptors and their regional distribution in rat brain. 125I-SRTX receptors in the rat brain bind the toxin rapidly and with high affinity. The binding was not inhibited by ligands of known neurotransmitter receptor and ion channels. 125I-SRTX receptors have a distinctive regional distribution. The highest densities were observed in the cerebellum, thalamus and hypothalamus (850, 550 and 450 fmol/mg protein, respectively) and the lowest densities in the caudate and cerebral cortex (82 and 62 fmol/mg protein, respectively). Taken together our results suggest that mammalian brains contain a hitherto undetected neuroreceptor that may operate in neurotransmission with a "SRTX-like" brain peptide, similar to the SRTX homologous vasoconstrictor peptide of the mammalian endothelium endothelin.

Animals↗
PubMed1988

Acetylcholine in the rat pituitary: a possible humoral factor.

Significant amounts of acetylcholine (ACh) were detected in each of the 3 lobes of the rat pituitary (3-6 pmol/anterior lobe, 3 pmol/intermediate lobe and 1.8 pmol/posterior lobe). In the anterior lobes of cyclic rats the levels of ACh varied with the estrous cycle, with daily peaks being observed on the days of proestrus and estrus. The occurrence of ACh, apparently as a humoral factor, appears to be unique to the anterior pituitary.

Acetylcholine↗
PubMed1988

Evidence for an endogenous factor involved in maintenance of pirenzepine high-affinity binding in rat brain stem.

Sucrose gradient centrifugation was used to isolate membranes enriched in muscarinic receptors from bovine brain stem. Unlike the receptors in crude synaptosomal preparations of this tissue, the enriched preparations displayed only low-affinity pirenzepine binding. Similar results were obtained when purified preparations were preincubated for 1 hr in pH 7.0 buffer at 37 degrees C; however, preincubation in a pH 5.0 buffer partially restored the high-affinity pirenzepine binding. These results suggest that an endogenous factor, which is present in the crude synaptosomes of the brain stem and is removed by sucrose gradient centrifugation, is involved in maintenance of the high-affinity pirenzepine binding of the muscarinic receptors.

Animals↗
PubMed1988

Carboxyl residue(s) at the ligand-binding site of rat muscarinic receptors.

Chemical modification of muscarinic receptors of rat cerebral cortex, brain stem and atria by a carboxyl-group-specific reagent, namely trimethyloxonium ion (TMO+) reduces the number of tritium-labeled antagonist- and agonist-binding sites in a dose-dependent way. No such effect is observed when modification is carried out in the presence of atropine, oxotremorine or carbamylcholine. These findings suggest that TMO+ specifically methylates the carboxyl residue(s) positioned at the binding site in members of the M1 and M2 receptor family.

Affinity Labels↗
PubMed1988

Sarafotoxin, a novel vasoconstrictor peptide: phosphoinositide hydrolysis in rat heart and brain.

Sarafotoxins, a group of 21-residue cardiotoxic peptides from snake venom that induce coronary vasoconstriction, show high-affinity binding to rat atrial and brain membranes and activate the hydrolysis of phosphoinositides. Neither their binding nor their activity is affected by blockers or activators of known receptors and ion channels, suggesting that sarafotoxins act either directly on the phosphoinositide phosphodiesterase system or on a novel receptor. Their amino acid sequence shows a high degree of homology with that of endothelin, a recently described 21-residue vasoconstrictor peptide found in porcine aortic endothelium. This is remarkable, since endothelin is a natural compound of the mammalian vascular system while sarafotoxins are highly toxic components of snake venom.

Amino Acid Sequence↗
PubMed1988

Guanosine 5'-triphosphate binding protein (Gi) and two additional pertussis toxin substrates associated with muscarinic receptors in rat heart myocytes: characterization and age dependency.

The coupling of muscarinic receptors with G-proteins was investigated in cultured myocytes prepared from the hearts of newborn rats. The coupling was investigated in both young (5 days after plating) and aged (14 days after plating) cultures, in view of the completely different effects of 5'-guanylyl imidodiphosphate [Gpp(NH)p] on muscarinic agonist binding to homogenates from young vs aged cultures [Moscona-Amir, E., Henis, Y. I., Yechiel, E., Barenholz, Y., & Sokolovsky, M. (1986) Biochemistry 25, 8118-8124]. Pretreatment of cultures from both ages by Bordetella pertussis toxin (IAP) was found to eliminate any Gpp(NH)p effect on carbamylcholine binding. IAP by itself induced a rightward shift in the carbamylcholine competition curve in homogenates from aged cultures, but no such effect was observed in homogenates from young cultures. IAP-catalyzed [32P]ADP-ribosylation of membrane preparations from young and aged cultures revealed major differences between them. Young cultures exhibited a major IAP substrate at 40 kDa, which was also recognized by anti-alpha i antibodies, and two novel IAP substrates at 28 and 42 kDa, which were weakly ADP-ribosylated by the toxin and were not recognized with either anti-alpha i or anti-alpha o antibodies. In aged cultures, only the 40-kDa band (ribosylated to a lower degree) was detected. The parallel age-dependent changes in the three IAP substrates (28, 40, and 42 kDa) and in the interactions of the G-protein(s) with the muscarinic receptors strongly suggest close association between the two phenomena. All of these age-dependent changes in the G-protein related parameters were prevented by phosphatidylcholine-liposome treatment of the aged cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate Ribose↗
PubMed1988

Chemical modification of rat cerebral cortex M1 muscarinic receptors: role of histidyl residues in antagonist and agonist binding.

Chemical modification of muscarinic M1 receptors in a synaptoneurosomal preparation of rat cerebral cortex by a hydrophilic histidyl-group-specific reagent, diethylpyrocarbonate (DEP), reduces the number of [3H]-4NMPB binding sites in a dose-dependent way. The effect can be reversed by hydroxylamine treatment. No such effect is observed when carbethoxylation with 2.5 mM DEP is carried out in the presence of atropine, 4NMPB, pirenzepine or carbachol. These findings indicate that DEP specifically modifies histidyl residue(s) positioned at the binding site in members of the M1 receptor family. However, treatment with 2.5 mM DEP in the presence of various muscarinic ligands significantly disturbs the binding state of agonists. The results suggest that M1 receptors may have more than one histidyl residue of importance in ligand binding.

Animals↗
PubMed1988

Mode of binding of [3H]dibenzocycloalkenimine (MK-801) to the N-methyl-D-aspartate (NMDA) receptor and its therapeutic implication.

Binding of the labeled anticonvulsant drug [3H]dibenzocycloalkenimine [(3H]MK-801 to the N-methyl-D-aspartate (NMDA) receptor and its dissociation from the receptor at 25 degrees C are slow processes, both of which follow first order kinetics (t1/2 approximately equal to 70 and 180 min, respectively). Both reactions are markedly accelerated by glutamate and glycine (t1/2 approximately equal to 5-8 and 4 min, respectively), which allow bimolecular association kinetics of the labeled drug with the receptors whereas equilibrium binding of [3H]MK-801 (Kd 2-4 nM) is hardly affected by glutamate and glycine. The data suggest that MK-801 acts as a steric blocker of the NMDA receptor channel. The competitive antagonist D-(-)-2-amino-5-phosphovaleric acid (AP-5) freezes the receptor in a state which precludes either binding of [3H]MK-801 to the receptor channel or its dissociation from it. These findings have therapeutic implications.

2-Amino-5-phosphonovalerate↗
PubMed1988

Kinetic characterization of the phencyclidine-N-methyl-D-aspartate receptor interaction: evidence for a steric blockade of the channel.

The nature of the interactions between the N-methyl-D-aspartate (NMDA) and the phencyclidine (PCP) receptors was studied in membranes obtained from rat cerebral cortex and washed repeatedly to remove endogenous excitatory amino acids. Binding of [3H]-N-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP) to its receptor sites in these membranes proceeded slowly and did not reach equilibrium even after incubation for 4 h at 25 degrees C. The dissociation rate of [3H]TCP-receptor complexes was also slow (t1/2 = 128-165 min). Both association and dissociation followed first-order reaction kinetics, with similar time constants (0.0054 min-1). Addition of glutamate and glycine to the washed membranes was immediately followed by a marked increase in the rates of both association of [3H]TCP with the receptors and its dissociation from them (t1/2 = 8 min). Association now followed second-order reaction kinetics. Accelerated association of [3H]TCP with its binding sites could also be induced by NMDA or by glutamate alone, and glycine enhanced the effect. All effects of glutamate and glycine on [3H]TCP binding kinetics were blocked by the competitive NMDA receptor antagonist AP-5 [D-(-)-2-amino-5-phosphovaleric acid]. [3H]TCP-receptor interactions at equilibrium were not altered by AP-5 or by glutamate and glycine. The binding data were fitted to a model in which interactions of [3H]TCP with the receptor involve a two-step process: the outside ligand must cross a barrier (presumably a closed NMDA receptor channel in the absence of agonists). Once agonists are added, this limitation is removed (presumably because the channel is open).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

G-protein mediates voltage regulation of agonist binding to muscarinic receptors: effects on receptor-Na+ channel interaction.

Our previous experiments in membranes prepared from rat heart and brain led us to suggest that the binding of agonists to the muscarinic receptors and to the Na+ channels is a coupled event mediated by guanine nucleotide binding protein(s) [G-protein(s)]. These in vitro findings prompted us to employ synaptoneurosomes from brain stem tissue to examine (i) the binding properties of [3H]acetylcholine at resting potential and under depolarization conditions in the absence and presence of pertussis toxin; (ii) the binding of [3H]batrachotoxin to Na+ channel(s) in the presence of the muscarinic agonists; and (iii) muscarinically induced 22Na+ uptake in the presence and absence of tetrodotoxin, which blocks Na+ channels. Our findings indicate that agonist binding to muscarinic receptors is voltage dependent, that this process is mediated by G-protein(s), and that muscarinic agonists induce opening of Na+ channels. The latter process persists even after pertussis toxin treatment, indicating that it is not likely to be mediated by pertussis toxin sensitive G-protein(s). The system with its three interacting components--receptor, G-protein, and Na+ channel--is such that at resting potential the muscarinic receptor induces opening of Na+ channels; this property may provide a possible physiological mechanism for the depolarization stimulus necessary for autoexcitation or repetitive firing in heart or brain tissues.

Acetylcholine↗
PubMed1988

Cloned M1 muscarinic receptors mediate both adenylate cyclase inhibition and phosphoinositide turnover.

The rat M1 muscarinic receptor gene was cloned and expressed in a rat cell line lacking endogenous muscarinic receptors. Assignment of the cloned receptors to the M1 class was pharmacologically confirmed by their high affinity for the M1-selective muscarinic antagonist pirenzepine and low affinity for the M2-selective antagonist AF-DX-116. Guanylyl imidodiphosphate [Gpp(NH)p] converted agonist binding sites on the receptor, from high-affinity to the low-affinity state, thus indicating that the cloned receptors couple to endogenous G-proteins. The cloned receptors mediated both adenylate cyclase inhibition and phosphoinositide hydrolysis, but by different mechanisms. Pertussis toxin blocked the inhibition of adenylate cyclase (indicating coupling of the receptor to inhibitory G-protein), but did not affect phosphoinositide turnover. Furthermore, the stimulation of phosphoinositide hydrolysis was less efficient than the inhibition of adenylate cyclase. These findings demonstrate that cloned M1 receptors are capable of mediating multiple responses in the cell by coupling to different effectors, possibly to different G-proteins.

Acetylcholine↗