UPTAKE AND RECEPTOR-SITES FOR GLYCINE IN ISOLATED BOVINE ADRENAL-MEDULLA CHROMAFFIN CELLS

H-3!Glycine is actively taken up into bovine isolated adrenal medulla chromaffin cells with the subsequent catecholamine release. H-3!Glyc ine uptake has two interaction sites based on relative K(m) measuremen ts. These sites are inherently distinct since the effects of strychnin e and temperature on glycine binding are significantly different. The high affinity site (K(m) = 6 x 10(-7) M) is strychnine-sensitive and i ts activity is unaltered at 4-degrees-C. These results point to a rece ptor-like function. The low-affinity site (K(m) = 1.4 x 10(-3)) is str ychnine-insensitive and is significantly inhibited (75%) by low temper ature (4-degrees-C), by low Na+ concentration and 50% by ouabain (10(- 4) M). Compounds structurally similar to glycine and known to antagoni ze its uptake to neuronal cells, such as beta-alanine, N-methyl-d,1-al anine and sarcosine, also inhibit the low affinity site which indicate a glycine uptake function for this site. The relative activity of the uptake inhibitors indicate that in the adrenal chromaffin cell, glyci ne uptake is carried out by a System A amino acid transporter mechanis m. GABA does not affect glycine binding or uptake in the chromaffin ce lls, suggesting that these two inhibitory amino acid neurotransmitters act via different mechanisms in the adrenal medulla. The results for glycine activity in adrenal medulla chromaffin cells are remarkably si milar to those seen in CNS neuronal cells, and thus support the use of chromaffin cells as a model system for studying the mechanism of acti on. of glycine in the central nervous system.