Ionic mechanisms of the rapid (nicotinic) phase of acetylcholine response in identified Planobarius corneus neurones.

Current responses to acetylcholine (ACh) and to suberyldicholine (D-6) applied from the double-barrelled ionophoretic micropipette were studied in two identified neurones (LPed-2 and LPed-3) isolated from the left ganglion of pulmonate mollusc, Planorbarius corneus. Experiments made with K2SO4-filled microelectrodes show that in LPed-2 neurone two kinds of cholinoreceptors are involved in the rapid phase of ACh response one of which induces chloride conductance and the other, sodium conductance. The Cl-dependent component can be separated from the cationic one by C-6 whereas the cationic component can be separated from the Cl--dependent one by furosemide. Cl- conductance can be induced selectively by D-6. In the LPed-3 neurone only Cl- conductance increases during rapid phase of ACh response. The reversal potential of Cl--dependent responses was found to be more negative than the resting potential in experiments made with K2SO4-filled microelectrodes but less negative than the resting potential in the case of KCl-filled microelectrodes. This difference seems to be due to the artificial increase of intracellular chloride concentration.