4.12 NEUROMODULATORS: TAURINE AND β-ALANINETaurine (2-aminoethanesulfonic acid; 4.235) is an inhibitory neurochemical that prob-
ably acts primarily as a neuromodulator rather than a neurotransmitter. It is formed
from cysteine, and its accumulation can be prevented by the cardiac glycoside ouabain.
Although receptor sites and specific actions cannot be elucidated without an antagonist,
taurine has been implicated in epilepsy and, potentially, in heart disease. There are a
large number of physiological effects attributed to taurine, among them cardiovascular
(antiarrythmic), central (anticonvulsant, excitability modulation), muscle (membrane
stabilizer), and reproductive (sperm motility factor) activity. Analogs of taurine,
phthalimino-taurinamide (4.236) and its N-alkyl derivatives, are less polar than taurine
and are potent anticonvulsant molecules.
Like taurine,β-alanine (4.237) is an inhibitory neuromodulator in the human CNS.
Numerous studies support this observation:β-alanine occurs naturally in the CNS, is
released by electrical stimulation, has binding sites, and inhibits neuronal excitability.
Structurally,β-amino acids (such as β-alanine) are intermediate between α-amino acids
(e.g., glutamate, glycine) and γ-amino acids (e.g., GABA). The existence of unique
β-alanine receptors is controversial, and no β-alanine antagonists have yet been identified.
However, studies have verified a dual action of β-alanine on both glutamatergic and
GABAergic processes. β-Alanine has five receptor sites: glycine co-agonist site on the
NMDA cation channel complex (strychnine insensitive); glycine receptor site (strychnine
sensitive); GABAAreceptor; GABAC(GABA-ρ) receptor; and blockade of “glial GABA
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