E. coli endotoxin affinity at the nicotinic2 receptor: receptor theory revisited, ilumina nostros occulae.
This paper examines the interaction of endotoxin at the nicotinic2 receptor (ACh-Rpost) with the adenylate cyclase signal transduction system in skeletal muscle. It reports the drug-receptor (DR) dissociation constant (K, 0.05020 +/- .0015 mg/kg) for E. coli endotoxin. It expands on a previous report (1) which presented the relevance of skeletal muscle cAMP as a metabolic indicator and second messenger influenced by endotoxicosis. The use of a murine endotoxic model allowed for the measuring of K for the antagonist. DR affinity measures which relied on the constrained-slope Schild plot measured it. This report assessed dose-response relations of the competitive antagonist dTC (AN) and their modification (AN') by advancing endotoxicosis. The presence of endotoxin at a fixed final concentration (i.e., 7.75 mg/kg) within the body at the end of a two week period caused a rightward shift in the dTC dose-response curve. Endotoxin desensitized cAMP and caused the dTC curve to be shifted rightward. This report differs from typical pharmacological applications where standard agonist curves are obtainable in the presence of an antagonist. This in vivo model did not allow for the measurement of agonist ACh concentration. Therefore, the use of a pair of compounds (i.e., antagonistic dTC and agonistic endotoxin) and their effects (i.e., suppression of active tension and cAMP desensitization, respectively) allowed us to quantitate K. In summary, this report supports the hypothesis linking the nicotinic2 receptor to the adenylate cyclase signal transduction system and illustrates that endotoxicosis perturbed both.
Tomera
J F
JF
Clinical Pharmacology Laboratory, Shriners Burns Institute, Boston, MA.
Kukulka
S P
SP
Lilford
K
K
Martyn
J A
JA
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D000242:Cyclic AMP / Q000502:physiology; D004926:Escherichia coli; D008070:Lipopolysaccharides / Q000493:pharmacokinetics*; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects; D011978:Receptors, Nicotinic / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014403:Tubocurarine / Q000494:pharmacology
D008070:Lipopolysaccharides; D011978:Receptors, Nicotinic; D000242:Cyclic AMP; D000109:Acetylcholine; D014403:Tubocurarine