Amiloride is a well-known antagonist of ENaC, Na⁺/Ca²⁺, and Na⁺/H⁺ exchangers, nonselective cation channels, and voltage-gated K⁺ and Ca²⁺ channels^1-8. It has been extensively used as a probe for a wide variety of transport systems¹.

Acid-sensing ion channels (ASICs) are expressed in various sensory and central neurons. Six different ASIC subunits have been cloned, which are encoded by four genes (ASIC1–ASIC4). Amiloride is a nonselective ASIC blocker and the channels cloned all belong to the Amiloride-sensitive Na⁺-channel. The IC₅₀ values for Amiloride block of ASIC in PC12 cells are 0.2-0.7 µM⁹, values which are ~10–20 times lower than its block of ASICs in central¹⁰ and sensory neurons¹¹.

TRPP3, a member of the transient receptor potential (TRP) superfamily of cation channels, is a Ca²⁺-activated nonselective cation channel permeable to Ca²⁺, K⁺, Na⁺, Rb⁺, NH₄, and Ba²⁺, inhibited by Mg²⁺, H⁺, La³⁺, and Gd^{3+ 12-13}. TRPP3 is localized to a subset of taste receptor cells in the tongue, where it may play a crucial role in sour tasting, and to neurons surrounding the central canal of the spinal cord, where it may account for the long-sought proton-dependent regulation of the frequency of action potential. Amiloride inhibits TRPP3 channel activity in Xenopus oocytes with an IC₅₀ value of 143 µM¹⁴.