Permeability of the abdominal nerve cord of the American cockroach to fatty acids.
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Abdomen↗
Biomedical subjects
M E Eldefrawi
Publications and source records attributed to M E Eldefrawi.
A comparison of the toxinological characteristics of two Cassiopea and Aurelia species.
A comparison of the toxinological properties of nematocyst venoms from Old and New World Cassiopea and Aurelia species was undertaken. The cnidom of venomous Cassiopea andromeda (Ca) and Aurelia (Aa(RS)) from the Red Sea was identical to that of nonvenomous Bahamian Cassiopea xamancha (Cx) and Chesapeake Bay Aurelia aurita (Aa(CB)), respectively. A clean nematocyst preparation of Ca and both Aurelias could be obtained but algal particles could not be separated completely from the Cx nematocysts. Further purification of all four nematocyst preparations showed significant differences in the action of their protein. Only the Cassiopea had coexisting dermonecrotic and vasopermeability producing properties and Ca's hemolytic activity was associated with mouse lethality. The protein, hemolysin and phospholipase gel filtration eluant curves of Ca venom were similar. Venomous Aa(RS) actively stung lips and contained more potent mouse lethal, demonecrotic, vasopermeability plus hemolytic factors than Aa(CB). Cross reactivity of convalescent human serum obtained from patients stung by Ca and venomous Cx collected in Central America occurred. This was also observed between sera of bathers stung by Aa(RS) and stinging Aurelia which appeared in Florida during the recent El Niño year. IgG was stimulated by several nematocyst proteins since many venom subfractions tested positive at high titers against convalescent sera. T-cell proliferation of mice primed with either Aurelia venom was positive against the homologous preparation with cross reactivity to the heterologous venom. Crude venoms of both Red Sea jellyfish metabolically stimulated cultured human hepatocytes more than their New World counterparts. This data shows that considerable similarities and differences exist in the venoms of these Old and New World Cassiopea and Aurelia medusae with the Eastern species being more potent.
Adult↗
Influence of the alcohol moiety of pyrethroids on their interactions with the nicotinic acetylcholine receptor.
Ten pyrethroids affected binding of [3H]perhydrohistrionicotoxin ([ 3H]H12-HTX) to the channel sites of the nicotinic acetylcholine (ACh) receptor/channel of the electric organ of the electric ray, Torpedo ocellata, and inhibited 45Ca2+ flux through the receptor's ionic channel. Most pyrethroids stimulated binding of [3H]H12-HTX to the channel sites in 30 s, in absence of carbamylcholine, with little or no effect on binding of [3H]ACh to the receptor sites, which suggests that the pyrethroids are binding to a third kind of site. However, in presence of carbamylcholine, all pyrethroids inhibited binding of [3H]H12-HTX, with esters of cyclopentenolone more potent, and generally more rapid in doing so, than esters of alpha-cyano-3-phenoxybenzyl alcohol. Changes in the acidic moiety of the pyrethroid had little effect. Kadethrin, whose alcohol moiety is 5-benzyl-3-furylmethyl, was the most potent pyrethroid in stimulating [3H]H12-HTX binding (in absence of carbamylcholine) in 30 s (18-fold) and in inhibiting it in 120 min. The pyrethroids were more potent in their modulation of [3H]H12-HTX binding at lower temperatures. Inhibition of receptor binding and receptor-regulated ion transport by concentrations of pyrethroids similar to those at which they affect nerve conduction suggests that the nicotinic ACh receptor may be an additional target for the toxic action of pyrethroids.
Acetylcholine↗
High affinity stereospecific binding of [3H] cocaine in striatum and its relationship to the dopamine transporter.
A high affinity (KD 35 nM) binding site for [3H]cocaine is detected in rat brain striatum present at 2-3 pmol/mg protein of synaptic membranes. This binding is displaced by cocaine analogues with the same rank order as their inhibition of [3H]dopamine ([3H]DA) uptake into striatal synaptosomes (r = 0.99), paralleling the order of their central stimulant activity. The potent DA uptake inhibitors nomifensine, mazindol, and benztropine are more potent inhibitors of this high affinity [3H]cocaine binding than desipramine and imipramine. Cathinone and amphetamine, which are more potent central stimulants than cocaine, displace the high affinity [3H]cocaine binding stereospecifically, but with lower potency (IC50 approximately equal to 1 microM) than does cocaine. It is suggested that the DA transporter in striatum is the putative "cocaine receptor." Binding of [3H]cocaine, measured in 10 mM Na2HPO4-0.32 M sucrose, pH 7.4 buffer, is inhibited by physiologic concentrations of Na+ and K+ and by biogenic amines. DA and Na+ reduce the affinity of the putative "cocaine receptor" for [3H]cocaine without changing the Bmax, suggesting that inhibition may be competitive. However, TRIS reduces [3H]cocaine binding noncompetitively while Na+ potentiates it in TRIS buffer. Binding of [3H]mazindol is inhibited competitively by cocaine. In phosphate-sucrose buffer, cocaine and mazindol are equally potent in inhibiting [3H]mazindol binding, but in TRIS-NaCl buffer cocaine has 10 times lower potency. It is suggested that the cocaine receptor in the striatum may be an allosteric protein with mazindol and cocaine binding to overlapping sites, while Na+ and DA are allosteric modulators, which stabilize a lower affinity state for cocaine.
Alkaloids↗
Allosteric regulation by sodium of the binding of [3H]cocaine and [3H]GBR 12935 to rat and bovine striata.
Sodium regulation of ligand binding to the dopamine transporter of rat and/or bovine striata was investigated using a filtration binding assay. In low Na+ phosphate or bicarbonate-buffered sucrose (300 mOsm), the tissue exhibited high affinity for [3H]cocaine which was reduced by the addition of Na+ in a dose-dependent manner. However, [3H]GBR 12935 binding was insensitive to Na+ in these physiological buffers. Although binding of [3H]GBR 12935 was displaced by cocaine in a manner consistent with competitive displacement, a non-linear affinity shift of the displacement of [3H]GBR 12935 by cocaine suggests that the two ligands bind to distinct sites. Binding of both radioligands was suppressed when measured in sodium-free 50 nM Tris-sucrose and increased with the addition of Na+. Scatchard analysis indicated that Bmax for [3H]cocaine binding in Tris plus 120 mM NaCl reached the same level as in the physiological buffers. In Krebs-Ringer buffer with phosphate, bicarbonate or Tris, which contained 120 nM NaCl, both [3H]cocaine and [3H]WIN 35428 binding exhibited lower affinities than in Na(+)-deficient phosphate buffer. It is suggested that the cation form of Tris binds to the dopamine transporter and that the Tris-receptor complex does not bind [3H]cocaine or [3H]GBR 12935. Na+ displaces Tris, forming a Na(+)-receptor complex which binds these ligands. Thus, it is suggested that the Na(+)-dependent binding of cocaine to the dopamine transporter is observed only in Tris.
Allosteric Regulation↗