The three-ion test for the identity of the ionophores mediating the hyperpolarizing response to cholinomimetics in neurones of Helix aspersa.
1. The hyperpolarizing response investigated is mediated by Cl- ions. Additional anions NO-3 and BrO-3 were introduced into the perfusate to produce a system with 3 permeant anions. 2. Under such circumstances the reversal potential (Er) becomes a means of discriminating between the molecular mechanisms invoked by different agonists that produce an increase in anionic conductance. 3. A statistically significant difference of 0.49 mV was detected between the Er for acetylcholine and those for acetyl-beta-methyl choline and tetramethylammonium (acetylcholine more negative). 4. This difference was not significantly affected by changing to a different 3-ion solution. 5. It is argued from theoretical grounds that a change in this difference is to be expected when molecular mechanisms differ; alternative explanations for the difference are suggested.
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D006372:Helix, Snails / Q000187:drug effects*; D007476:Ionophores / Q000032:analysis*; D008564:Membrane Potentials / Q000187:drug effects; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D010277:Parasympathomimetics / Q000494:pharmacology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology
D007476:Ionophores; D008688:Methacholine Compounds; D010277:Parasympathomimetics; D000644:Quaternary Ammonium Compounds; D016210:Methacholine Chloride; C027917:tetramethylammonium; D000109:Acetylcholine