Bimodal action of glycine on frog spinal motoneurones.

In the presence of procaine the changes in electrical potential caused by glycine in the ventral root of the isolated hemisected spinal cord of the frog have been shown to be compounded of both hyperpolarizing and depolarizing responses to the amino acid. From a comparison of the effects of changes in the perfusion medium on the potentials produced by glycine, beta-alanine and L-glutamate in the presence and absence of strychnine, it was concluded that glycine acts on a similar receptor to beta-alanine and causes a hyperpolarizing response which is blocked by strychnine. However, glycine has an additional, depolarizing, action which is usually the major effect and masks the hyperpolarizing response. The depolarizations produced by L-glutamate and glycine could be differentiated by their different ionic dependencies. The glycine depolarization was selectively decreased by a lowered sodium ion concentration in the medium while L-glutamate depolarizations were selectively enhanced by lowered potassium ion concentration.