Abstract

The action of polymethylene bis-ammonium compounds on acetylcholine-activated channels was investigated on voltage-clamped neurons of the isolated rabbit superior cervical ganglion. The kinetics of complex formation by the compound and the open channel was determined from shortening of decay of the fast excitatory postsynaptic current, the rate of which corresponds to the rate of channel closure, whereas the kinetics of dissociation of this complex was determined by recovery of the second response to application of two pulses of acetylcholine. With membrane hyperpolarization complex formation was found to be accelerated, and its dissociation retarded. The potential-dependence of interaction between compound and channel increases with lengthening of the polymethylene chain. Variation of one of the two cationic groups in a compound with a tetramethylene chain does not affect potential-dependence. In a series of bis-ammonium compounds, ganglion-blocking activity, determined on the cat superior cervical ganglionin situ was found to correlate with the velocity constant of binding with the open channel. It is concluded that the ganglion-blocking action of bis-ammonium compounds is determined by their channel-blocking activity.

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