Table 4. EC₅₀ and maximum effect values for amino acid-evoked exchange of [³H]L-serine from rat hippocampal astrocyte cultures.

Amino acid	Astrocyte Exchange
	EC50 μM	Max. Effect %	N
L-alanine	178±77	90±6.4	4
L-threonine	69.1±21.2	88.2±4.4	3
L-cysteine	27.2±10.8	53.5±2.1	4
L-serine	135±16	100	15
D-serine	2139±630	104±6	4
L-proline	5267±1975	41.4±10.4	3
L-glutamine	41.6±5.7	37.3±6.6	6
t-Pro	22.3±4.7	63.2±7.5	4

Values are the mean ± SEM of n observations. t-Pro is L-trans-4-hydroxyproline.