Biomedical subjects

S E Senogles

Publications and source records attributed to S E Senogles.

23 records · Page 2Linked to original sources

PubMed1982

A comparison of peripheral and central human muscarinic cholinergic receptor affinities for psychotropic drugs.

A peripheral model offers a valuable research tool for the investigation of central cholinopathic disorders. The in vitro affinities of several psychotropic drugs for the muscarinic cholinergic binding sites of human caudate and erythrocyte were compared in competition with a tritiated antagonist (quinuclidinyl benzilate). The relative affinities of the drugs for both tissues were strikingly similar. Thus, the erythrocyte muscarinic receptor may represent an accessible in vitro assay for the characterization of central cholinopathic states.

Binding, Competitive↗

PubMed1981

Stimulation of guanylate cyclase by EDTA and other chelating agents.

The partially purified soluble guanylate cyclase (GTP pyrophosphatelyase(cyclizing), EC 4.6.1.2) from human caudate nucleus is stimulated from 2 to 4-fold by metal chelating agents. EDTA (K 1/2 - 4.8 microM) is more potent than CDTA (K 1/2 = 13.2 microM) or EGTA (K 1/2 = 21.8 microM) at stimulating activity. Stimulation by chelating agents is apparently not due to removal of inhibitory divalent cations which contaminate the enzyme or reaction mixture. EDTA increases guanylate cyclase activity in part by increasing the affinity of the enzyme for the substrate (MgGTP) 10-fold. Dopamine inhibits partially purified guanylate cyclase in the presence or absence of EDTA. Dopamine increases the Ka of guanylate cyclase for the activator, free Mn2+, more than 50-fold, from 3 to 150 microM.

Caudate Nucleus↗

PubMed1981

Postmortem stability of dopamine-sensitive adenylate cyclase, guanylate cyclase, ATPase, and GTPase in rat striatum.

The stability of dopamine-sensitive adenylate cyclase, guanylate cyclase, ATPase, and GTPase was measured in homogenates of rat striatal tissue frozen from 0 to 24 h postmortem. ATPase, GTPase, and Mg2+-dependent guanylate cyclase activities showed no significant change over this period. Mn2+-dependent guanylate cyclase activity was stable for 10 h postmortem. Basal and dopamine-stimulated adenylate cyclase activity decreased markedly during the first 5 h. However, when measured in washed membrane preparations, these adenylate cyclase activities remained stable for at least 10 h. Therefore, the postmortem loss of a soluble activator, such as GTP, may decrease the adenylate cyclase activity in homogenates. These results are not consistent with an earlier suggestion that there is a postmortem degradation of the enzyme itself. Other kinetic parameters of dopamine-sensitive adenylate cyclase can also be measured independently of postmortem changes. Thus, it is possible to investigate kinetic parameters of dopamine-sensitive adenylate cyclase, guanylate cyclase, ATPase, and GTPase in human brain obtained postmortem.

Adenosine Triphosphatases↗

PubMed1980

Catecholamine-sensitive guanylate cyclase from human caudate nucleus.

Partial purification of soluble guanylate cyclase on DEAE-Sephacel yields two separate peaks of guanylate cyclase activity. After 10-fold purification of the soluble enzyme, guanylate cyclase is markedly inhibited by micromolar concentrations of dopamine (I50 = 0.2 microM). Dopamine inhibition is observed whether the reaction is conducted with Mn2+ or with Mg2+, under atmosphere or N2(g), and using enzyme from either peak from the DEAE-Sephacel column. Other catecholamines also inhibit partially purified guanylate cyclase with an order of potency at 1 microM of: dopamine = L-DOPA > norepinephrine = isoproterenol = adrenochrome > epinephrine. The structural requirements for inhibition are two free hydroxyl groups on the phenyl ring and an ethylamine side chain. Dopamine also inhibits the Triton X-100-solubilized microsomal guanylate cyclase after partial purification on DEAE-Sephacel. Neither chlorpromazine, propranolol, nor phentolamine at 20 microM effectively block the dopamine inhibition of partially purified soluble guanylate cyclase. Micromolar concentrations of the reducing agents dithiothreitol and glutathione also inhibit partially purified guanylate cyclase, but unlike these agents, catecholamines can inhibit whether added in the reduced or the oxidized forms. Inhibition of enzyme activity by micromolar concentrations of dopamine, adrenochrome, or dithiothreitol is rapidly reversed by dilution and the dopamine inhibition is competitive with MgGTP. Inhibition does not appear to involve covalent binding or to result from the ability of catecholamines to reduce the concentrations of oxygen or free radicals in solution.

Adrenochrome↗

PubMedDate not supplied

Ionic regulation of antagonist binding to the human muscarinic cholinergic receptor of caudate nucleus.

In this in vitro study we investigated the effects of a variety of cations on binding of the cholinergic antagonist, (3H)-quinuclidinyl benzilate, to the human caudate. Physiologic sodium concentrations induced a state of positive cooperativity upon the human muscarinic cholinergic receptor (nHill = 1.41). Lithium at therapeutic equivalency (1 mM) was unique in increasing the dissociation constant (KD) for this antagonist from 35.9 to 72.4 pM. This implies a lithium-induced cholinomimetic effect at the human muscarinic receptor consistent with reports of the reversal of mania by physostigmine. These findings are also relevant to previous cholinergic receptor studies in which various cations have been employed.

Caudate Nucleus↗