Category: receptor_pharmacology
Explains the characteristic tingle/itch felt 10-20 min after a bolus dose of β-alanine — the most user-noticed and most-asked-about side effect of the supplement. β-alanine is a low-affinity but selective agonist of MrgprD (Mas-related G protein-coupled receptor D), a Gq-coupled GPCR expressed on a discrete subpopulation of non-peptidergic C-fiber sensory neurons that innervate skin (Shinohara 2004 identified the receptor; Liu 2012 mapped the itch circuit). Activation drives PLCβ → IP3 → intracellular Ca²⁺ release → depolarization → action potentials in MrgprD⁺ afferents, perceived centrally as paresthesia (tingle, prickle, mild itch) localized to face, scalp, neck, and back — the regions with the densest MrgprD⁺ innervation. The sensation is dose-dependent and saturable; slow-release / split-dose formulations blunt it by keeping plasma β-alanine below the activation threshold (Trexler 2015). Mechanism is histamine-independent — antihistamines don't blunt it — which is why it reads as 'tingle' rather than 'itch' to most users. Downstream channel discrimination: TRPC3 is dispensable (Dong 2017); the conducting current is more likely a calcium-activated chloride channel (TMEM16A/anoctamin-1) and TRPA1-dependent in the longer-tail neuropathic context. Bellinger 2016 shows paresthesia does not impair endurance-cycling performance — useful clinical reassurance.