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

Executive Summary: Amiloride (MK-870) is a potent epithelial sodium channel (ENaC) inhibitor and urokinase-type plasminogen activator receptor (uPAR) modulator used in ion channel research (APExBIO). It blocks sodium influx in epithelial tissues with high specificity under physiological conditions (Wang et al., 2018). Amiloride is valuable for dissecting sodium channel signaling and endocytic pathways in disease models such as cystic fibrosis and hypertension. Experimental use requires strict storage at -20°C and prompt preparation of solutions to maintain stability. Published studies confirm its use in benchmarking ENaC and endocytosis assays, although it shows no inhibition of clathrin-mediated viral entry in certain cellular models (Wang et al., 2018).

Biological Rationale

Amiloride (MK-870) is a pyrazine derivative that selectively inhibits epithelial sodium channels (ENaC) and urokinase-type plasminogen activator receptors (uPAR). ENaC is essential for sodium balance and fluid homeostasis in epithelial tissues, including kidney, lung, and colon. Dysregulation of ENaC activity is implicated in diseases such as cystic fibrosis, hypertension, and pulmonary edema (see related article). Amiloride is widely used to model and modulate sodium transport mechanisms in vitro and in vivo. uPAR is involved in cellular signaling, migration, and endocytosis. Dual inhibition enables researchers to dissect signaling pathways relevant to epithelial function and disease.

Mechanism of Action of Amiloride (MK-870)

Amiloride (MK-870) acts by reversible blockade of ENaC at the extracellular face of the channel. This inhibition reduces sodium influx into epithelial cells, altering downstream signaling and transepithelial ion transport. The compound also modulates uPAR, impacting cellular uptake and migration. As a PC2 channel blocker, it influences polycystin-2-mediated calcium signaling. The molecular weight is 229.63 Da (C₆H₈ClN₇O), and it is typically supplied as a solid to be stored at -20°C (APExBIO product BA2768). Solutions are unstable over time and should be freshly prepared prior to use.

Evidence & Benchmarks

• Amiloride (MK-870) at 50 µM shows no inhibition of clathrin-mediated endocytosis of genotype III grass carp reovirus in CIK cells, indicating specificity boundaries for viral entry assays (Wang et al., 2018).
• ENaC inhibition by Amiloride leads to measurable decreases in sodium current in patch-clamp assays (typically >90% blockade at 10–100 µM, depending on cell system; see comparative review for disease modeling context).
• Amiloride is commonly used as a mechanistic tool in epithelial ion transport and signaling studies across mammalian and model organism systems (see strategic guidance).
• It is not effective as a general endocytosis inhibitor in all contexts; its primary activity is restricted to ENaC/uPAR pathways (Wang et al., 2018).

Applications, Limits & Misconceptions

Amiloride (MK-870) is validated for the following research applications:

• Sodium channel research—quantification of ENaC function and pharmacological inhibition.
• Cellular endocytosis modulation—selective studies of uPAR and ENaC-related uptake mechanisms (see mechanistic endocytosis analysis). This article extends prior work by explicitly benchmarking Amiloride against clathrin-mediated entry in aquatic virology.
• Disease modeling—cystic fibrosis, hypertension, and pulmonary epithelial function.
• Benchmarks for epithelial sodium channel signaling and receptor pathway studies.

Common Pitfalls or Misconceptions

• Amiloride does NOT inhibit clathrin-mediated endocytosis in all systems; its effect is context-dependent (e.g., no effect in GCRV104 entry to CIK cells at 50 µM, Wang et al., 2018).
• It is NOT suitable for long-term solution storage; degradation affects activity (must use freshly prepared solutions, see APExBIO).
• Amiloride is NOT a general virus entry inhibitor and should not be used as a broad-spectrum antiviral control.
• It is intended strictly for research use and NOT for diagnostic or medical applications (product notice).
• Higher concentrations may have off-target effects; titration is required for specificity.

Workflow Integration & Parameters

Amiloride (MK-870) is provided by APExBIO as a stable solid (BA2768) for research use (product page). Store at -20°C; ship with Blue Ice for small molecules. Prepare working solutions in aqueous buffer or DMSO immediately before use. Do NOT freeze/thaw solutions repeatedly. For sodium channel assays, typical concentrations range from 1 to 100 µM; optimal dosing depends on cell system and endpoint (see advanced modulation guide; this article updates prior guidance with recent aquatic virology benchmarks). Confirm compound identity and purity by referencing the certificate of analysis from APExBIO.

Conclusion & Outlook

Amiloride (MK-870) remains a cornerstone tool for epithelial sodium channel and uPAR research. Its specificity for ENaC and validated use in cellular uptake assays makes it indispensable for disease modeling and mechanistic studies. However, its activity is pathway- and context-dependent, underscoring the importance of experimental design and specificity controls. For the latest workflows, researchers should reference both product documentation and recent peer-reviewed literature.