Electric organ polyamines and their effects on the acetylcholine receptor

Abstract

1. The electric organ of Torpedo nobiliana contained putrescine (PUT), spermidine (SPD), spermine (SPM), and cadaverine (CAD). Traces of acetylated SPD and SPM were occasionaly seen. 2. Upon fractionation of the tissue by differential centrifugation, the polyamines (PA) were found predominantly in the soluble fraction. The postsynaptic membrane fraction, containing a high concentration of acetylcholine receptor (AChR), was proportionally enriched in SPM. The molar ratio of SPM to AChR was approximately two in these membranes. 3. The effect of exogeneous PA on AChR function was studied by two methods: carbamoylcholine (CCh)-dependent 86Rb+ influx into receptor-rich membrane vesicles and [alpha-125I]bungarotoxin (Bgt) binding to the AChR. 4. SPM inhibited both ion influx and the rate of Bgt binding at concentrations above 1 mM, and therefore it appears to act as a competitive antagonist of the AChR. 5. At submicromolar concentrations, and only after preincubation with the receptor-rich membrane, SPM and PUT increased the ion influx by about 20% over control values. 6. Preincubation with 100 nM SPM did not affect the equilibrium binding of iodinated toxin or the rate of toxin binding, and therefore SPM was not uncovering new receptors. 7. By measuring the initial rate of toxin binding after different periods of preincubation with 1 microM CCh, the rate of the slow phase of receptor desensitization was determined. This rate was not changed by 100 nM SPM. 8. Although these results suggest that at low concentrations SPM is a positive modulator of the AChR, the precise mechanism of action is not determined yet.

Transfection of Myoblasts in Primary Culture with Isomeric Cationic Cholesterol Derivatives

“…Polyamines 1/1 by weight) for primary dog myoblasts using pTG11033 coding for were also shown to bind to and modulate the nicotinic firefly luciferase. Transfections were performed at charge ratio 1, acetylcholine receptor (28,29). Both acetylcholine and which was optimal for both transfection agents (8.5 and 20.4 mg/ml NMDA receptors are present on skeletal muscle fiber total lipid at 10 mg/ml DNA for spermidine-cholesterol / DOPE and Lipofectin, respectively).…”

In vitro selection of RNA molecules that displace cocaine from the membrane-bound nicotinic acetylcholine receptor

“…Preparation of Torpedo californica Electroplax Membrane and Determination of AChR Concentration. The method of preparation was modified from the methods described by Szczwinska et al (52). Frozen T. californica electric organs were purchased from Pacific Bio-Marine (Venice, CA).…”

Polyamines as Snake Toxins and Their Probable Pharmacological Functions in Envenomation

“…Szczawinska et al [116] likewise found that at concentrations above 1 mM, spermine inhibited ion influx and α-bungarotoxin binding to Torpedo electric organ nAChRs, thereby acting as a competitive antagonist of the nAChR. In contrast, at sub-µM concentrations, spermine enhanced cation influx by about 20%, effectively acting as an nAChR agonist.…”