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PubMed1977

Secretion of monoquaternary ammonium compounds by guinea pig small intestine in vivo.

In anesthetized guinea pigs N-(3H)methylscopolamine (NMScop), N1-(14C)methylnicotinamide (NMN), and (14C)tetraethylammonium (TEA), administered intravenously, were secreted against a concentration gradient into the lumen of the small intestine. The concentration ratio of unmetabolized ammonium base in the intestinal lumen to that in the plasma was 4.3 and 6.5 for NMScop and NMN, respectively, 75 min after the intravenous injection of 1 nmole/g body weight of the individual compounds. The corresponding value for TEA after 180 min was 2.0. The establishment of the concentration gradient between intestinal lumen and plasma was diminished with increasing doses. An excess of NMN inhibited the uphill transport of NMScop. Since the electrical potential difference across the intestinal epithelium and a 'fluid circuit' mechanism cannot solely account for the observed accumulation of the monoquaternary ammonium compounds in the intestinal lumen, the evidence presented supports previous in vitro findings that the small intestine is capable of actively secreting organic cations.

Animals↗
PubMed1991

Quaternary ammonium compounds as structural probes of single batrachotoxin-activated Na+ channels.

Quaternary ammonium (QA) blockers are well-known structural probes for studying the permeation pathway of voltage-gated K+ channels. In this study we have examined the effects of a series of n-alkyl-trimethylammonium compounds (Cn-QA) on batrachotoxin (BTX)-activated Na+ channels from skeletal muscle incorporated into planar lipid bilayers. We found that these amphipathic QA compounds (Cn-QA where n = 10-18) block single Na+ channels preferentially from the internal side with equilibrium dissociation constants (KD) in the submicromolar to micromolar range. External application of amphipathic QA compounds is far less effective, by a factor of greater than 200. The block can be described by a QA molecule binding to a single site in the Na+ channel permeation pathway. QA binding affinity is dependent on transmembrane voltage with an effective valence (delta) of approximately 0.5. QA dwell times (given as mean closed times, tau c) increase as a function of n-alkyl chain length, ranging from approximately 13 ms for C10-QA to 500 ms for C18-QA at +50 mV. The results imply that there is a large hydrophobic region within the Na+ channel pore which accepts up to 18 methylene groups of the Cn-QA cation. This hydrophobic domain may be of clinical significance since it also interacts with local anesthetics such as cocaine and mepivacaine. Finally, like BTX-activated Na+ channels in bilayers, unmodified Na+ channels in GH3 cells are also susceptible to QA block. Amphipathic QA cations elicit both tonic and use-dependent inhibitions of normal Na+ currents in a manner similar to that of local anesthetic cocaine. We conclude that amphipathic QA compounds are valuable structural probes to study the permeation pathway of both normal and BTX-activated Na+ channels.

Animals↗
PubMed1990

Immunoassays employing substituted ammonium compounds other than neuromuscular blocking drugs to increase the detection of IgE antibodies to these drugs.

Subjects who experience life-threatening anaphylactic reactions to neuromuscular blocking drugs frequently have serum IgE antibodies that react with substituted ammonium groups on the drugs. Failure to detect drug-reactive antibodies may be due to the nature of the drug-solid support used for testing sera. With this in mind, solid phases of some selected compounds containing substituted ammonium groups, in particular triethylamine and morphine, were prepared and used to screen sera in an attempt to increase the frequency of detection of IgE antibodies complementary to tertiary and/or quaternary ammonium groups. For subjects who experienced an anaphylactic reaction to succinylcholine or gallamine, use of the supplementary assays increased the frequency of detection from 83 to 100%. For d-tubocurarine and alcuronium, detections increased from 92 to 100% and from 67 to 88%, respectively. Molecular models revealed a clear structural similarity between the conformations of the trialkylammonium groups on one face of the molecules of morphine and d-tubocurarine.

Anaphylaxis↗