Cholinoreceptive membrane inactivation caused by the depolarization of Lymnaea stagnalis neurones

Abstract

1. The relationship between the peak currents produced by iontophoretically applied acetylcholine (ACh) and voltage has been found to be non-linear, the slope of the relationship decreasing with the membrane depolarization. The possible causative factors of this phenomenon have been studied. 2. The membrane depolarization does not influence main cholinoreceptive membrane characteristics such as an apparent dissociation constant ( K D ), the Hill coefficient ( K H ), the reverse potential ( V r ) and the desensitization rate constants. 3. The membrane depolarization does not alter ACh concentration near the outer membrane surface. 4. The individual ACh-opened channels do not posses the rectifying properties. 5. The conclusion has been made that the decrease in the slope of the current-voltage ( I- V) relation, named by us “inactivation”, is accounted for by a transition of the cholinoreceptors into a state, in which they no longer have the ability to form the opened ionic channels in spite of ACh presence in the bath.