GLYCINE INDUCES 2 DISTINCT MEMBRANE CURRENTS IN NEONATAL RAT SYMPATHETIC PREGANGLIONIC NEURONS IN-VITRO

1. The effects of glycine (Gly) on neonatal (12- to 16-day-old) rat sympathetic preganglionic neurones (SPNs) in transverse (500 mu m) thoracolumbar spinal cord slices were studied by whole-cell patch-clamp techniques. 2. Gly elicited three types of membrane currents when applied to SPNs by pressure ejection (100 mM; 20-180 ms pulse duration): (1) an outward current (20/94 cells); (2) an inward current (30/94); and (3) a biphasic response (44/94) consisting of an outward followed by an inward current. 3. The Gly-induced outward current (I-Gly,I-out) had a mean reversal potential of -67 mV, was reversed in a low (5.7 mM) chloride Krebs solution, and was reversibly eliminated by strychnine (0.1-1 mu M). 4. The Gly-induced inward current (I-Gly,I-in) had a mean reversal potential of -41 mV, was reduced in a Na+-free and increased in a high (15 mM) K+ solution; strychnine at the high concentration of 1 mu M reduced the response by an average of 53%. 5. The electrophysiological and pharmacological characteristics of the biphasic response suggest that it was a combined response of outward and inward currents. 6. The results show that Gly elicits two distinct membrane currents, a Cl--dependent outward current and a cationic inward current, which are mediated by strychnine-sensitive and strychnine-resistant Gly receptors. Functionally, activation of both types of Gly receptors reduces neuronal excitability and attenuates synaptic transmission.