Ionic Basis Of Membrane-Potential And Of Acetylcholine-Induced Currents In The Cell Body Of The Cockroach Fast Coxal Depressor Motor-Neuron

Summary The ionic basis of the resting potential and of the response to acetylcholine (ACh) has been investigated in the cell body membrane of the fast coxal depressor motor neurone in the metathoracic ganglion of the cockroach Periplaneta americana. By means of ion-sensitive microelectrodes, intracellular concen- trations of three ion species were estimated (mmoll"1): (K+)j, 144±3; (Na+)j, 9±1; (Cl~),, 7±1. The resting potential of continuously superfused cells was -75.6±1.9mV at 22CC. A change in resting potential of 42.0±2.5mV ac- companied a decade change in (K +) o. Experiments with (10~ 4 molP1) ouabain, Na + injection, low temperature (10°C) and non-superfused cells indicated the presence of an electrogenic sodium pump. Under current-clamp, the cell body membrane was depolarized by sequentially applied, ionophoretic pulses (500ms duration) of ACh. Under voltage-clamp, such doses of ACh resulted in an inward current which was abolished in low-Na+ saline. Ion-sensitive electrodes revealed an increase in (Na