A positively charged guanidium-containing quinazoline that modulates ASIC function by blocking acid-induced maximal peak current as well as by altering ASICs pH dependence for activation and inactivation, enabling a partial, but sustained ASIC3 activation around neutral pH (4.4% of pH 5-induced peak current with 1mM GMQ at pH 7.4), which is inhibitable by Amiloride. Intraplantar paw injection (10ul 100uM) is reported to elicit a pain response in asic3+/+, but not asic3-/-, mice in vivo. GMQ targeting area appears to overlap with Amiloride binding site in the pore region, but is distinct from ASIC calcium binding site.