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Biomedical subjects

J MacDermot

Publications and source records attributed to J MacDermot.

At least 91 records · Page 5Linked to original sources
PubMed1982

Prostaglandins D2 and E2 are not regulators of amino acid release from rat cortical synaptosomes.

Rat cerebral cortex synaptosomes synthesise prostaglandins, and analysis by gas chromatography-mass spectrometry revealed that of the prostaglandins quantified PGD2 (10.9 ng/mg protein) was produced in highest concentration. Treatment with high potassium or veratrine caused release of putative amino acid transmitters, but not of prostaglandins, and prostaglandins D2 and E2 were unable to stimulate release of amino acids. The release of putative amino acid transmitters, evoked by high potassium levels, was not inhibited by these prostaglandins. Prostacyclin receptors could not be identified on synaptosomes by radioligand binding techniques.

Amino Acids↗
PubMed1982

Desensitization of prostacyclin receptors in a neuronal hybrid cell line.

1 Prostacyclin and its stable analogue, carbacyclin, bind competitively to a single population of receptors, and activate adenylate cyclase of the NCB-20 neuronal somatic cell hybrid (Kact = 40.1 nM and 96.1 nM respectively). 2 Culture of NCB-20 cells in the presence of 1 microM carbacyclin for 4 to 16 h results in a progressive decrease in the prostacyclin-dependent activation of adenylate cyclase in cell homogenates with an increase at 16 h of the Kact from 64.1 nM to 174.0 nM and decrease in the maximum adenylate cyclase activation from 41.2 to 15.1 pmol cyclic AMP min-1 mg-1 protein. 3 The prediction that the apparent decrease in affinity in the prostacyclin-dependent activation of adenylate cyclase was secondary to a reduction in receptor numbers was tested directly by measuring binding of [3H]-prostacyclin to membranes of cells exposed to carbacyclin for 16 h. This showed an actual decrease in affinity of the prostacyclin-receptor interaction, as well as a decrease in the total receptor numbers. Thus prolonged exposure of NCB-20 cells to carbacyclin caused reductions in both receptor numbers and affinity, reflected by measurements both of binding and adenylate cyclase activation.

Adenylyl Cyclases↗
PubMed1981

Prostacyclin binding to guinea pig pulmonary receptors.

[3H] Prostacyclin bound to membranes of guinea pig lung. Specific binding was saturable, and the results revealed two receptor classes (Kd =16 nM and 258 nM). The binding capacity of the high affinity site was 105 fmol [3H]prostacyclin per mg of membrane protein, and that of the low affinity site was 1257 fmol per mg membrane protein. A comparison of selected prostaglandins as inhibitors of [3H] prostacyclin binding revealed some of the structural requriements of the ligand for occupation of the high affinity receptor.

Animals↗
PubMed1981

Forearm ischaemia as a test of prostacyclin production: studies in normal subjects and in patients with diabetes mellitus.

Plasma levels of 6-oxo-PGF1 alpha, the hydrolysis product of prostacyclin, were significantly reduced in men with proliferative diabetic retinopathy, compared with normal controls. Male diabetics with background or no retinopathy formed an intermediate group with plasma levels of 6-oxo-PGF1 alpha lower than controls and higher than patients with proliferative retinopathy. Forearm ischaemia increased plasma levels of 6-oxo-PGF1 alpha by 30% in normal subjects. The increase occurred during arterial occlusion and was diminished by pretreatment with aspirin. The increase after ischaemia may reflect increased prostacyclin production. In diabetic patients forearm ischaemia produced an increase in plasma 6-oxo-PGF1 alpha similar to that seen in control subjects.

6-Ketoprostaglandin F1 alpha↗
PubMed1981

The binding of [3H]-prostacyclin to membranes of a neuronal somatic hybrid.

1 [3H]-prostacyclin bound to a washed membrane preparation of the NCB-20 neuronal hybrid cell line. 2 Kinetic analysis of [3H]-prostacyclin binding suggested a simple, non-cooperative bimolecular interaction between the ligand and a single receptor population. The equilibrium dissociation constant was 16.6 nM, and binding at a saturating [3H]-prostacyclin concentration enabled the receptor density of 2.57 x 10(5) receptor molecules per cell to be calculated. 3 At 20 degrees C the rate constant for the forward reaction (K+1) was 2.26 x 10(5) M-1 S-1, and the rate constant for the dissociation of the ligand-receptor complex (k-1) was 3.85 x 10(-3) S-1. Thus the dissociation constant (k-1/k+1) was 17.0 nM. 4 Prostaglandin E1 and prostacyclin compete for a single receptor in these cells, and comparison of other prostaglandins as inhibitors of [3H]-prostacyclin binding revealed some of the structural requirements for high-affinity occupation of prostacyclin receptors.

Adenylyl Cyclases↗
PubMed1981

Divalent cations increase [3H]-prostacyclin binding to membranes of neuronal somatic hybrid cells.

1 [3H]-prostacyclin binding to membranes of a highly differentiated neuronal somatic hybrid is increased equally in the presence of Ca2+, Ba2+, Mg2+ or Sr2+ ions. 2 Analysis of the binding of [3H]-prostacyclin in the presence of low (1 mM) or high (50 mM) Mg2+ ion concentrations has revealed a cation-dependent increase in ligand receptor affinity (Kd values = 57.4 nM and 21.9 nM). 3 The increase in [3H]-prostacyclin binding due to divalent cations is not accompanied by an alteration in the maximum binding capacity of the membranes.

Animals↗
PubMed1980

The morphology of rat soleus neuromuscular junctions treated in vitro with purified beta-bungarotoxin.

Pairs of isolated rat soleus nerve-muscle preparations were maintained in vitro in oxygenated Ringer solution containing 3 microgram/ml beta-bungarotoxin prepared by the method of MacDermot et al. End-plate potentials and twitch tensions generated in response to continuous stimulation via the nerve at 0.5 Hz were recorded from one muscle, while miniature end-plate potential amplitude and frequencies were monitored in the corresponding unstimulated member of the pair. The results obtained were compared with the fine structure of end-plates from identical preparations sampled after varying periods of intoxication, and from unpoisoned muscles maintained for comparable times in vitro. The electron micrographs obtained were analyzed quantitatively using simple stereological techniques. Our results show that: (1) nerve terminal synaptic vesicle content declines for the first hour of intoxication but returns to near normal levels following conduction block; (2) there is a rapid increase in the 'coated' vesicle population of the nerve terminals, both attached to the plasmalemma and within the terminal cytoplasm, which persists to the end of the experiment; and that (3) there is no significant increase in the incidence of damaged mitochondria within the poisoned nerve terminals. These findings are discussed in relation to previous observations and the putative mechanisms of action of beta-bungarotoxin.

Animals↗
PubMed1980

Activation of guinea pig pulmonary adenylate cyclase by prostacyclin.

Prostacyclin activates adenylate cyclase of guinea pig lung homogenates. The concentration for half-maximum activation was 20 nM. Kinetic analysis of the increase in enzyme activity suggested a non-cooperative, bimolecular interaction between prostacyclin and a single receptor population. Comparison of the activity of prostacyclin with that of other prostaglandins revealed a rank order of potency: prostacyclin > prostaglandin E1 > prostaglandin E2 > prostaglandin F1 alpha. 6-Oxo-prostaglandin F1 alpha, the stable hydrolysis product of prostacyclin, produced no increase in adenylate cyclase activity. Lungs were dissected before homogenisation, and prostacyclin-sensitive adenylate cyclase was identified at high concentrations in peripheral lung tissue containing small airways, blood vessels and parenchyma. The precise cellular location of these receptors remains obscure, but the probability that they are in the pulmonary vascular bed rather than airway smooth muscle is discussed.

Adenylyl Cyclases↗
PubMed1980

Prostacyclin-dependent activation of adenylate cyclase in a neuronal somatic cell hybrid: prostanoid structure-activity relationships.

1 Prostacyclin activates adenylate cyclase of the NCB-20 neuronal hybrid cell line. 2 There is a guanosine 5'-triphosphate requirement for the activation of adenylate cyclase by 5,6 beta-dihydroprostacyclin (a stable analogue of prostacyclin). 3 Steady-state kinetic analysis of the activation of adenylate cyclase by 5,6 beta-dihydroprostacyclin suggests a simple non-cooperative bimolecular interaction between the ligand and single receptor population. 4 Structure-activity relationships of selected prostanoids elucidated certain functional requirements for activation of adenylate cyclase.

15-Oxoprostaglandin 13-Reductase↗
PubMed1980

Abnormal regulation of prolactin release in idiopathic Parkinson's disease.

Levodopa with carbidopa suppressed prolactin release induced by thyrotrophin releasing hormone less effectively in patients with idiopathic Parkinson's disease than in normal subjects. This finding supports the view that the biochemical defect in idiopathic Parkinson's disease extends to the hypothalamus and is not confined to the basal ganglia. Aetiological considerations in Parkinson's disease should encompass a widespread disorder of neurotransmission whose extent merits further investigation.

Adult↗
PubMed1979

Adenylate cyclase and acetylcholine release regulated by separate serotonin receptors of somatic cell hybrids.

Serotonin activates adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] of NCB-20 neuroblastoma--brain hybrid cells with an activation constant of 530 nM, but has little or no effect on cellular cyclic AMP or cyclic GMP content of NIE-115 neuroblastoma or NG108-15 hybrid cells. In homogenates of NCB-20 hybrid cells, lysergic acid diethylamide stimulates adenylate cyclase activity (Kact = 12 nM) and partially inhibits (Ki = 10 nM) the stimulation of adenylate cyclase activity by serotonin. No desensitization was detected of serotonin receptors coupled to adenylate cyclase. Serotonin also depolarizes NCB-20, NG108-15, and NIE-115 cells and increases acetylcholine release. Serotonin receptors mediating depolarizing responses desensitize rapidly and reversibly, and the depolarizing effects of serotonin are neither mimicked nor inhibited by lysergic acid diethylamide. These results indicate that (i) NCB-20 cells possess at least two species of serotonin receptors, which independently regulate cellular functions, (ii) activation of adenylate cyclase does not directly affect membrane potential or acetylcholine release, and (iii) serotonin-dependent cell depolarization does not affect cyclic AMP or cyclic GMP synthesis in the cell lines tested.

Acetylcholine↗