title: Conductance increases produced by bath application of cholinergic agonists to Electrophorus electroplaques.
abstract: When solutions containing agonists are applied to the innervated face of an Electrophorus electroplaque, the membrane's conductance increases. The agonist-induced conductance is increased at more negative membrane potentials. The "instantaneous" current-voltage curve for agonist-induced currents is linear and shows a reversal potential near zero mV; chord conductances, calculated on the basis of this reversal potential, change epsilon-fold for every 62-mV change in potential when the conductance is small. Conductance depends non-linearly on small agonist concentrations; at all potentials, the dose-response curve has a Hill coefficient of 1.45 for decamethonium (Deca) and 1.90 for carbamylcholine (Carb). With agonist concentrations greater than 10(-4) M Carb or 10(-%) M Deca, the conductance rises to a peak 0.5-1.5 min after introduction of agonist, then declines with time; this effect resembles the "desensitization" reported for myoneural junctions. Elapid alpha-toxin, tubocurarine, and desensitization reduce the conductance without changing the effects of potential; the apparent dissociation constant for tubocurarine is 2 X 10(-7) M. By contrast, procaine effects a greater fractional inhibition of the conductance at high negative potentials.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity / Q000187:drug effects*; D004557:Electric Organ / Q000187:drug effects*; D004593:Electrophorus; D066298:In Vitro Techniques; D008564:Membrane Potentials; D010276:Parasympatholytics / Q000494:pharmacology*; D011343:Procaine / Q000494:pharmacology; D013997:Time Factors; D014118:Toxins, Biological / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D010276:Parasympatholytics; D014118:Toxins, Biological; D011343:Procaine; D014403:Tubocurarine