Effects produced on inhibitory postsynaptic potentials by the coupled injections of cations and anions into motoneurons

Abstract

Ions have been injected into cat motoneurons impaled by a double microelectrode. Current has been passed down one barrel and up the other, so injecting cations out of the former and anions out of the latter. The injection of (K + + Cl - ) ions gave a depolarizing shift of the E IPSP almost as large as for a Cl - ion injection, and with a time course comparable with that for injections of Cl - or K + ions alone. The injection of (Na + + Cl - ) ions displaced the E IPSP by much the same amount and again the recovery time was almost as fast as after a Cl - ion injection, and much faster than after the injection of Na + ions alone. On the other hand injection of (2Na + + SO 2 4 - ions caused a slight displacement of the E IPSP in the hyperpolarizing direction. It was postulated that, when (K + ) i is depleted, there is an accelerated operation of an inward pump for (K + + Cl - ) ions with the consequence that the decline of high (Cl - ) i is slowed by a factor of three or more. The ion injection procedures did not provide evidence for or against the participation of K + ion movements in the generation of the IPSP , but this participation at a level comparable with that of Cl - ions had to be postulated in order to account for the normal hyperpolarizing character of the IPSP .