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What confers specificity on glycine for its receptor site?

1 The structural requirements for activation of the glycine receptor were studied in isolated ventromedial hypothalamic neurones of rats by use of a ‘concentration‐clamp’ technique under single‐electrode voltage‐clamp conditions. 2 α‐Amino acids (l‐α‐alanine, and d‐α‐alanine, and l‐serine), and glycine‐methylester, glycine‐ethylester and β‐amino acids (β‐alanine and taurine) produced a transient inward Cl− current, which was similar to that induced by glycine. 3 The responses to individual α‐ and β‐amino acids were selectively antagonized by strychnine, but were not affected by bicuculline, picrotoxin or the taurine antagonist, TAG (6‐aminomethyl‐3‐methyl‐4H,1,2,4‐benzothiadiazine‐1,1‐dioxide hydrochloride), suggesting that α‐ and β‐amino acids activate the same glycine receptor. 4 β‐Amino acids were slightly more potent than the α‐amino acids in causing cross‐desensitization of the glycine response. 5 From the results of the structure‐activity analysis of the optical isomers of α‐alanine, serine and cysteine, a tentative structure of the glycine receptor is proposed.