ω-Agatoxin IVA TFA is a potent, selective P/Q type Ca2+ (Cav2.1) channel blocker with IC50s of 2 nM and 90 nM for P-type and Q-type Ca2+ channels, respectively. ω-Agatoxin IVA TFA (IC50, 30-225 nM) inhibits glutamate exocytosis and calcium influx elicited by high potassium. ω-Agatoxin IVA TFA also blocks the high potassium-induced release of serotonin and norepinephrine. ω-Agatoxin IVA TFA has no effect on L-type or N-type calcium channels.