Ganglion-blocking activity of dequalinium in frog and rat sympathetic ganglia in vitro.

The effect of dequalinium on ganglionic transmission and responses to exogenous acetylcholine receptor agonists were studied in frog and rat sympathetic ganglia. In frog ganglia, dequalinium reduced ganglionic transmission (measured using gross extracellular recording) with an EC50 of 2 microM. At 1 microM, dequalinium produced non-surmountable antagonism of the ganglion depolarization evoked by nicotinic receptor activation. Dequalinium reduced the amplitude of evoked and spontaneous excitatory postsynaptic potentials recorded intracellularly from frog neurones, but had no effect on the action potential elicited by injection of a depolarizing current pulse. Hyperpolarizing and depolarizing responses to muscarine recorded extracellularly from frog ganglia were antagonized by 3 microM dequalinium. In rat ganglia, synaptic transmission and depolarization by an exogenous nicotinic agonist were only slightly inhibited by dequalinium at a concentration of 100 microM. At 30 microM, dequalinium produced a 17% reduction in the depolarization of this tissue by muscarine (1 microM). These results add to the evidence of the diversity of nicotinic and muscarinic acetylcholine receptors, and indicate that dequalinium may be a valuable tool for the study of these receptors. However its usefulness as a probe for calcium-activated potassium channels may be limited by its actions at acetylcholine receptors.