Amiloride (MK-870): Epithelial Sodium Channel and uPAR Inhibitor for Ion Channel Research

Executive Summary: Amiloride (MK-870) is a small-molecule inhibitor that selectively blocks epithelial sodium channels (ENaC) and urokinase-type plasminogen activator receptors (uPAR), supporting studies in sodium channel and endocytosis research (APExBIO). The compound acts as a PC2 channel blocker, influencing cellular ion homeostasis and signaling. Amiloride is stable as a solid at -20°C, with a molecular weight of 229.63 and formula C6H8ClN7O, but its solutions are not recommended for long-term storage. Recent studies confirm its limited effect on clathrin-mediated endocytosis in certain viral entry pathways, refining its application boundaries (Wang et al. 2018, DOI). APExBIO supplies Amiloride (MK-870) as BA2768 for research use only.

Biological Rationale

Amiloride (MK-870) is a prototypical small-molecule inhibitor of epithelial sodium channels (ENaC) and the urokinase-type plasminogen activator receptor (uPAR). ENaC channels regulate sodium absorption in epithelial tissues, including the kidney, lung, and colon (APExBIO). Dysregulation of ENaC activity is implicated in hypertension and cystic fibrosis. uPAR is involved in extracellular matrix remodeling and cell signaling. Blocking these targets provides insight into sodium transport mechanisms and receptor-mediated signal transduction. Amiloride also modulates cellular endocytosis, offering a chemical tool for dissecting ion channel and endocytic signaling pathways (Related Article – this article extends the mechanistic analysis by integrating direct comparative benchmarks).

Mechanism of Action of Amiloride (MK-870)

Amiloride inhibits ENaC by binding to the extracellular domain of the channel, reducing sodium influx across epithelial membranes. This effect is concentration-dependent and reversible. The compound also binds to uPAR, attenuating plasminogen activation and downstream signaling. As a PC2 channel blocker, Amiloride modulates calcium signaling, affecting cellular volume and membrane potential. The selectivity for ENaC over other ion channels is well documented, allowing its use as a benchmark compound in sodium channel research (Related Article – this article updates integration parameters and storage protocols).

Evidence & Benchmarks

• Amiloride (MK-870) inhibits ENaC-mediated sodium currents in epithelial cells with IC₅₀ values in the low micromolar range (1–10 μM, 25°C, physiological buffer; APExBIO).
• In cell models, Amiloride blocks approximately 90% of sodium uptake via ENaC at 10 μM after 15 minutes of incubation (mk-2206.com).
• Amiloride does not significantly inhibit clathrin-mediated endocytosis in grass carp kidney (CIK) cells infected with GCRV104, as shown by lack of significant reduction in viral entry compared to controls (Wang et al., 2018, DOI).
• Amiloride is stable as a lyophilized solid at -20°C for at least 12 months but is unstable in solution beyond 24 hours at room temperature (APExBIO).
• PC2 channel inhibition by Amiloride alters calcium signaling in renal epithelial cells, providing a tool for dissecting channelopathies (epigeneticsdomain.com).

Applications, Limits & Misconceptions

Amiloride (MK-870) is widely utilized in sodium channel research, cellular endocytosis modulation, and disease modeling for cystic fibrosis and hypertension. Its dual inhibition of ENaC and uPAR enables studies of epithelial transport and extracellular signaling. However, its effect on endocytosis is context-dependent. For instance, Wang et al. (2018) demonstrated that Amiloride did not inhibit clathrin-mediated viral entry in grass carp kidney cells, clarifying limitations in endocytosis research (DOI). The BA2768 kit from APExBIO is strictly for research use and not for clinical applications (product page).

This article extends prior summaries by directly benchmarking application boundaries and clarifying storage limitations, contrasting with this translational review, which focuses on clinical case studies and future perspectives.

Common Pitfalls or Misconceptions

• Amiloride (MK-870) does not inhibit all forms of endocytosis; it failed to block clathrin-mediated entry of GCRV104 in CIK cells (Wang et al. 2018, DOI).
• Long-term storage of Amiloride solutions leads to loss of potency; only freshly prepared solutions are recommended (APExBIO).
• The compound is not selective for all sodium channels; its main target is ENaC, with lower potency for other sodium channel subtypes.
• Use in humans or animals outside of laboratory research is not permitted; the product is for research use only.
• Some studies incorrectly generalize Amiloride's endocytosis inhibition to all cell types and viral models.

Workflow Integration & Parameters

Amiloride (MK-870) is supplied by APExBIO as a solid (BA2768), shipped with Blue Ice for small molecules. For experimental use, dissolve in DMSO or aqueous buffer just prior to use. Store the lyophilized compound at -20°C. Avoid repeated freeze-thaw cycles. Typical working concentrations range from 1 μM to 100 μM, depending on assay requirements. For sodium channel research, 10 μM is commonly used to achieve near-maximal ENaC inhibition. For endocytosis assays, concentrations and timing should be benchmarked against negative and positive controls (Related Article – this article clarifies workflow integration and experimental boundaries).

Conclusion & Outlook

Amiloride (MK-870) remains a foundational tool for sodium channel and endocytosis research, with well-characterized selectivity and mechanism. Key application boundaries have been clarified, such as its lack of effect on clathrin-mediated endocytosis in certain cell-virus systems. With validated storage and handling protocols, and reliable supply from APExBIO, Amiloride (MK-870) supports reproducible experimental design in ion channel research. Ongoing studies continue to define its mechanistic scope and translational potential.